High idle after driving

[S.hafsmo]

Yes, another idle topic.
My recent test drive revealed a few issues, and increased idle after driving is one of them.
When starting the car cold, it idles fine at approx. 7-800 RPM. At this point I can rev the car, even drive a little, but after it has reached operating temperature, it will not return to proper idle after driving or revving the engine. It's almost like it sticks to the coasting idle (1200 RPM) and won't return to normal.

It serves to mention that I've just been doing some work below the plenum, and I do not know if this was an issue before this work was carried out.
All gaskets are new, as well as all sub-plenum vacuum parts (hoses, grommets, actuators etc.), and I have eliminated most of these as the culprit by blocking of their vacuum supply. And regardless, would not a vacuum leak be unaffected by engine temperature?

I've also had the throttle body off, and while having it off, I checked if the DAG material was still there, which it was not. But again, would this be affected by temperature?

Found the primary throttle blade to be a bit small. This can't seal very well.
http://imagizer.imageshack.us/v2/800x600q90/924/jyMoKh.jpg

I've checked the IAC, and it does close properly.

[Roadster]

Seems like we have similar problems.....lol
Do you have a Tech 1 or scanner that will read the IAC counts? It would be interesting to see what your IAC is at idle. Hopefully we will both get our issues resolved......Good luck!!!

[S.hafsmo]

I actually ordered a tech-1 about 5 minutes ago. Will post the IAC-count as soon as I receive it.

I did some testing today with the car in the garage, but was unable to provoke the high idle. Seems it must be properly hot /driven for this to occur. Did however see a slight increase (900rpm) after revving a bit when engine was hot.

I did another test, which was inducing a vacuum leak by unplugging one of the plenum outputs (revs increase), disconnected IAC (IAC closes?), then reconnecting the previously removed vacuum connector. Should this not result in idle lower than normal? Stop screw set point? Idle did however seem to lower only down to 900 rpm, and stay there.

Engine stops if air horn covered with a plate.

[G8nightman]

I had a similar issue I had the TB off and placed a light under it to see that a good amount of light passing the blades this was also before i knew that it was bad to clean the TB and removed the dag by mistake. My fix was replacing the dag and idle went to normal after that.

[S.hafsmo]

Can one replace the dag?

[ssrszz4]

Force 842 moly lube can be used. It's a spray on.

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[Roadster]

I actually ordered a tech-1 about 5 minutes ago. Will post the IAC-count as soon as I receive it.

I did some testing today with the car in the garage, but was unable to provoke the high idle. Seems it must be properly hot /driven for this to occur. Did however see a slight increase (900rpm) after revving a bit when engine was hot.

I did another test, which was inducing a vacuum leak by unplugging one of the plenum outputs (revs increase), disconnected IAC (IAC closes?), then reconnecting the previously removed vacuum connector. Should this not result in idle lower than normal? Stop screw set point? Idle did however seem to lower only down to 900 rpm, and stay there.

Engine stops if air horn covered with a plate.

From what I understand, if the engine stalls, then you are good with no vacuum leaks.

If you need to reset the IAC, this is from the FSM...
"Reset the IAC valve pintle position
A. Depress accelerator pedal slightly
B. Start and run engine for five seconds
C. Turn ignition "OFF" for ten seconds
D. Restart engine and check for proper idle operation"



I had a similar issue I had the TB off and placed a light under it to see that a good amount of light passing the blades this was also before i knew that it was bad to clean the TB and removed the dag by mistake. My fix was replacing the dag and idle went to normal after that.

Now that I am thinking about it, it may have been possible when I had the plenum out I may have removed some of the dag on the primary throttle...
:eek:

And yes, what did you use for the "dag"??? Was it the actual material, or something close to it???

[Roadster]

Force 842 moly lube can be used. It's a spray on.

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Sounds like I need to make a purchase.......:)

[ssrszz4]

Seems many throttle bodies use this factory applied dag stuff i did some research on may auto web site where they where having this same type of problem. Seems there's​the are a few different products that can be used but the force 842 seems to be the easiest to find they sell it on Amazon.

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[G8nightman]

It was a spray on i forgot the product I will take a picture and post when i get home.

[Roadster]

This may be another alternative.....:dontknow:

https://www.amazon.com/CRC-03084-Net-Weight-Lubricant/dp/B0013J62P4/ref=pd_sbs_328_1?_encoding=UTF8&pd_rd_i=B0013J62P4&pd_rd_r=32A4XK85HQ5ZSCY3T8Z2&pd_rd_w=cHfxD&pd_rd_wg=gEdZk&psc=1&refRID=32A4XK85HQ5ZSCY3T8Z2

[S.hafsmo]

Molycote D321R is also an option, but that one is rather expensive. I'll see what I can find locally, and do a little experiment.

A little googling shows that this is an issue on many cars. The Skyline RB26 for one. There's even a "throttle coat" out there.
http://www.tomei-p.co.jp/_2003web-catalogue/193_others_gauge.html

[Roadster]

Molycote D321R is also an option, but that one is rather expensive. I'll see what I can find locally, and do a little experiment.

A little googling shows that this is an issue on many cars. The Skyline RB26 for one. There's even a "throttle coat" out there.
http://www.tomei-p.co.jp/_2003web-catalogue/193_others_gauge.html

Interesting, is there anyway to transfer that into English???

Found it, also expensive...
https://store.outperformance.com/product-p/tomei-981019.htm

[S.hafsmo]

I've ordered a bottle from the Netherlands. It doesn't work like the OEM stuff, but if it doesn't work I assume it'll just wipe off.

[G8nightman]

https://uploads.tapatalk-cdn.com/20170427/b245f4ef23d59418232ace0bd4554508.jpghere is what I used


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[Roadster]

https://uploads.tapatalk-cdn.com/20170427/b245f4ef23d59418232ace0bd4554508.jpghere is what I used


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I already have that on the shelf....lol, but not the industrial strength. I sprayed that on my mailbox lock and the coating is still there on the inside from over two weeks ago.
I also ordered the CRC version listed in a previous post. Looks like my TB is coming off in the next few days....

[S.hafsmo]

I've ordered a bottle from the Netherlands. It doesn't work like the OEM stuff, but if it doesn't work I assume it'll just wipe off.

Just got the following reply from the Netherlands,
The Tomei Throttle coat is no longer available. We have the same stuff from Molykote available if you wish. Let me know if you prefer a refund or the alternate product.

I've asked to which product they refer.

Edit: They sell the Molykote D321R as a replacement, so I've ordered an aerosol bottle of it.

[ssrszz4]

I found it on eBay the throttle coat that is.
http://www.ebay.com.au/itm/181995009727

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[ssrszz4]

http://justjap.com/tomei-throttle-coat.html

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[S.hafsmo]

Seems like we have similar problems.....lol
Do you have a Tech 1 or scanner that will read the IAC counts? It would be interesting to see what your IAC is at idle. Hopefully we will both get our issues resolved......Good luck!!!

I've now received my Tech 1A and as expected, the IAC counts are 0 when the high idle occurs. I have not yet tested when it's cold.
When I parked today after a rather spirited drive, the idle was approx. 970 RPM, and after stop/start it stabilized at 770, so a 200 rpm drop by just restarting the car.

The Molykote D321R was stopped in transit, because it's "dangerous", so I've ordered it elsewhere. An expensive experiment at $120 for a bottle of spray.

Another issue has appeared, though probably unrelated. The battery voltage was 13.2 volts (on the Tech 1), which is way to low. Faulty voltage regulator? Increasing the revs did not seem to affect the voltage.

[A26B]

The problem may be in the ECM PROM. There are 3 different versions for the 1990 ZR-1, the original & 2 upgrade versions by GM to resolve issues, one of which was high idle.

Here are the 3 different calibration versions in the order of release. The number is on the PROM.

1990 ; 16129717, 16148554 & 16163905

[S.hafsmo]

Thanks Jerry, will the later releases lower the coasting idle?

Here's a picture of my prom, but I couldn't find the numbers to which you refer.
http://imagizer.imageshack.us/v2/1024x768q90/923/ZxhxEP.jpg

[Roadster]

I've now received my Tech 1A and as expected, the IAC counts are 0 when the high idle occurs. I have not yet tested when it's cold.
When I parked today after a rather spirited drive, the idle was approx. 970 RPM, and after stop/start it stabilized at 770, so a 200 rpm drop by just restarting the car.

The Molykote D321R was stopped in transit, because it's "dangerous", so I've ordered it elsewhere. An expensive experiment at $120 for a bottle of spray.

Another issue has appeared, though probably unrelated. The battery voltage was 13.2 volts (on the Tech 1), which is way to low. Faulty voltage regulator? Increasing the revs did not seem to affect the voltage.

My idle issue exactly, only I don't have to do a spirited drive for it to occur. It will happen either driving normally or getting into it a little bit. Yes, restarts are exactly the same, will drop to normal after every restart...
As you may know I am in the middle of another plenum pull, so when everything gets backs together, hopefully the issue will be resolved.

I would check the voltage on your battery with the key in the off position, IIROC it shouldn't be below 12.5v (can't remember) and then check again with engine running as you already have. Another way to check besides the Tech 1 which should be accurate is to use a meter and put the pins directly on the "P" and "N" terminals to get your reading. But you may already know that.....
You can also put a trickle charge on it to see if the battery will take and is fully charged.

[S.hafsmo]

I don't really have to do any spirited driving either, but at least this time I'm absolutely sure everything were at operating temperature.
Yes, I'm following your progress, hoping it'll solve the issue. Would be interesting to know what might cause such an intermittent idle problem.

[Roadster]

It might all come down to the TB, or in your case as Jerry as mentioned the PROM in the ECM, since yours is a 90. But IMO, I think we both have the same exact issue.....

[S.hafsmo]

I would check the voltage on your battery with the key in the off position, IIROC it shouldn't be below 12.5v (can't remember) and then check again with engine running as you already have. Another way to check besides the Tech 1 which should be accurate is to use a meter and put the pins directly on the "P" and "N" terminals to get your reading. But you may already know that.....
You can also put a trickle charge on it to see if the battery will take and is fully charged.

I'm sure I checked the charge voltage just after I bought the car, but I obviously have to re-check. To completely fill an acid battery approx. 14.4V is necessary from the charger/alternator. The battery should then read 12,7V when the battery is fully charged.
Unless it has some sort of "float charge" that occurs when the battery is full. I'll try to double check later today.

[WVZR-1]

A very long time ago I posted this PROM progression chart for the LT5. At that time I thought it to be "all inclusive" - I still believe so.

http://zr1.net/forum/attachment.php?attachmentid=3432

Your AUAH was a very early production PROM and you'd certainly be interested in either Marc's or the later AYBK. See the release dates in the chart.

I actually still have a couple of the GM AYBK PROM - original and I believe boxed still in GM package.

[S.hafsmo]

Much appreciated. How much would you take for one of the AYBK-PROMs? If you wish to sell one, that is.

Did you see the Starter service kit details I posted?

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[A26B]

Thanks Jerry, will the later releases lower the coasting idle?

Here's a picture of my prom, but I couldn't find the numbers to which you refer.

Your Prom, AUAH is the second release for 1990 MY. The final (3rd) release calibration is AYBK as WVZR-1 stated.
The following information excerpt was copied from Marc Haibeck's, Haibeck Automotive Technology website.

The performance calibration AYBKG is based on GM's latest release of the calibration for '90 LT5 engines. GM calibration AYBK was released as a service part via Product Service Bulletin 476503, dated February, 1994. It was released to address problems with idle fluctuation after a hot restart, increase in idle speed after a hot restart and excessive engine speed during coast down to a stop with the clutch disengaged.

The factory installed '90 calibration controls the Up-Shift lamp on the cluster. I don't know why, but GM disabled the up-shift lamp on the Service Part calibration AYBK. Because of that, AYBKG does not use the up-shift lamp.


Jerrys Gaskets sells USED PROMS which have been erased, reloaded with the latest calibration specific to each model year.
http://www.jerrysgaskets.com/eprom-prom-used-w-oem-calibration-90-95-14d1/

We will purchase outright or take your prom in exchange for $60. Payment or purchase exchange will be remitted after your PROM has been verified servicable.

[S.hafsmo]

Thanks. Now I've just got to figure out whether to go for the Haibeck chip, or a revised stock chip?

[XfireZ51]

Thanks. Now I've just got to figure out whether to go for the Haibeck chip, or a revised stock chip?

I'm pretty certain Marc would use the AYBK cal as the basis for any revised chip he would provide.

[rkreigh]

The problem may be in the ECM PROM. There are 3 different versions for the 1990 ZR-1, the original & 2 upgrade versions by GM to resolve issues, one of which was high idle.

Here are the 3 different calibration versions in the order of release. The number is on the PROM.

1990 ; 16129717, 16148554 & 16163905

Thx Jerry~!

the LT5 sometimes does an "idle step down" strategy where the car hovers above idle, once the car is at TPS zero for a bit it FINALLY goes back to idle

doesn't do this when cold, and the IAC isn't the issue, it's the code.

so what to do! see if you can borrow a prom with the latest stuff in it and chances are you will see what I mean.

my LSV has that strategy due to the big cams to prevent stalling, and it drives me NUTS. car is mild enough it really doesn't need it.

The right tuner can see this and program it out so the idle snaps back when you get off the throttle.

great posts about the dog gone dag My throttle body is a bit long in the tooth from many miles and smiles, and I also suspect my ASR mechanism is grouchy as my car hangs at 2k rpms until I blip the throttle, and then it goes through the whole mickey mouse drop to 1500 until I sit there at a light, and then after about no joke 20 seconds of idle time at zero TPS, it finally goes to a nice silky 1k idle.

Demps and I will be looking at this more in depth and report back. The LSV runs great but I'm getting a code 61 due to the secondary vacuum system (the air pump in the nose) crapping out. well I don't have secondaries so I don't need the pump but the dumb chip and pooter don't know it.

remember computers and light bulbs have equal intelligence, we still need actual not artificial intelligence, and the ZR-1 is just another challenge.

The old computer and memcals are a pain to work with, but it returns me to my mainframe roots when hex and binary were king.

kids now don't know what that means.:cry:

[XfireZ51]

Ron,

There shouldn't be anything in the calibration that would cause u to have a Code 61 unless the cal is not set to essentially ignore the secondary map readings.

[S.hafsmo]

I'm sure I checked the charge voltage just after I bought the car, but I obviously have to re-check. To completely fill an acid battery approx. 14.4V is necessary from the charger/alternator. The battery should then read 12,7V when the battery is fully charged.
Unless it has some sort of "float charge" that occurs when the battery is full. I'll try to double check later today.

I re-checked the voltage the other day, and at least when cold it does make 14 Volts. Can I measure at the ALDL connector to check what the Tech 1 is reading?`

I'm pretty certain Marc would use the AYBK cal as the basis for any revised chip he would provide.

I would assume as much, the question was more in term of actually wanting the additions of the Mark chip. I can't seem to find any downside to it though.

[TealZR1]

S.hafsmo-

Been following this - any resolve? Mine idle does the same thing

[S.hafsmo]

Unfortunately, not yet. I'm currently at work in Africa, and won't be back until the beginning of June. I've ordered Mark's chip, and I've got a bottle of Molykote D321R ready for DAG-replacement testing.

[Andreas]

Hi, did you replace the DAG, i'm curious for the result?

[S.hafsmo]

I didn't get around to it this trip either. Due to our short summers, other projects got priority (leaky roofs and such). I did however install the chip from Mark, and it certainly made great impact on coast-down idle, as well as idle when engine is hot. The issue is now only a minor one, and I assume it's due to worn throttle body. If mine is anywhere near as worn as Roadster's, the DAG would be just a band-aid, and a TB overhaul is due. Come autumn I will make an attempt on the DAG, but will probably end up sending the TB over to Haibeck this winter for an overhaul.

[lfalzarano]

I had to send my throttle body to Marc and the car has been fantastic after that!


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[Roadster]

Just to clarify, I never mentioned that my TB was worn.....besides doing the dag and the other items on my thread, my idle is perfect and the engine runs great. I don't co rider doing the dag a band aid fix, time consuming, yes..... band aid, no
JMO.....😁😁😁

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[Roadster]

Just to clarify, I never mentioned that my TB was worn.....besides doing the dag and the other items on my thread, my idle is perfect and the engine runs great. I don't consider doing the dag a band aid fix, time consuming, yes..... band aid, no
JMO.....😁😁😁

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[Roadster]

]Just to clarify, I never mentioned that my TB was worn.....besides doing the dag and the other items on my thread, my idle is perfect and the engine runs great. I don't consider doing the dag a band aid fix, time consuming, yes..... band aid, no
JMO.....😁😁😁

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[S.hafsmo]

Just to clarify, I never mentioned that my TB was worn.....besides doing the dag and the other items on my thread, my idle is perfect and the engine runs great. I don't co rider doing the dag a band aid fix, time consuming, yes..... band aid, no
JMO.....😁😁😁


The degree of wear I have only assumed based on the amount of light shining through on your photos. My secondary blades had nowhere near such amounts of light penetrating at the periphery. My primary however was quite bad.
The original layer of DAG on the TBs was also extremely thin, and not a multiple layer buildup.
Referance photo from ZR1Specialist.com (http://www.zr1specialist.com/HAT%20Web/services/DCP_0875.JPG)

I am not arguing the value of your effort, nor the result, as it is as you say, working perfectly. :)

I worry that if the wear I believe I can see on the photos is real, there will be minute axial play on the blades, which over time will start wearing out the applied DAG.

Hopefully my worries are unjustified, and a renewed layer of DAG is sufficient as a permanent fix. That would save me quite a few pennies (expensive to ship stuff across the Atlantic).

[BigJohn]

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Saved you a seat at our Powwow and a piece of fried bread with cinnamon and sugar on top!

[Roadster]

The degree of wear I have only assumed based on the amount of light shining through on your photos. My secondary blades had nowhere near such amounts of light penetrating at the periphery. My primary however was quite bad.
The original layer of DAG on the TBs was also extremely thin, and not a multiple layer buildup.
Referance photo from ZR1Specialist.com (http://www.zr1specialist.com/HAT%20Web/services/DCP_0875.JPG)

I am not arguing the value of your effort, nor the result, as it is as you say, working perfectly. :)

I worry that if the wear I believe I can see on the photos is real, there will be minute axial play on the blades, which over time will start wearing out the applied DAG.

Hopefully my worries are unjustified, and a renewed layer of DAG is sufficient as a permanent fix. That would save me quite a few pennies (expensive to ship stuff across the Atlantic).

I know your not trying to argue.....I just wanted to explain that to me a Band-Aid fix is a temp and quick fix....not intended for a long period of time....just wanted to bring to your attention that when you spend a decent amount of time on trying to correct a problem, it usually for a permanent solution not a temp one (which you already know);).....I try not to do Band-Aid fixes unless absolutely necessary. :)

Now to clear up the amount of light from the secondary blades.....when I first used the light test, there was no light coming through the secondary blades at all. That was shown and mentioned in one of my threads. Now to my understanding which was explained to me @ Carlisle, when the engines were tested, if they did not idle correctly, then the dag was applied to the secondary blades to correct the problem, and IMO maybe to the primary blade as mine had a sufficient amount of some substance that was applied to my primary blade. Now was it applied from the factory on the primary blade or applied sometime after, that I can't answer. Now to me that was a Band-Aid fix at the factory as opposed to properly seating the blades into the bores. Now as also explained to me is that not all engines required the dag to idle properly, hence why some TB's have the dag and some don't.....apparently some of the blades were seated correctly as opposed to the ones that were not!!!
So just because there is daylight coming through the secondary blades after dag removal, doesn't mean the TB is worn......JMO Now when I removed the TB, I decided to remove the dag completely and start over. Now it is and has been recommended not to remove any of the dag,[-X I did it anyway. Reason being is I wanted to start fresh to learn more about the TB and the application of the dag. I took a chance and it worked out for me.
The dag is a time consuming job....I don't think the dag will wear off as you mentioned above.....reason being is my dag did not wear off....and why do I say that....because of what I mentioned on the first test with the light not shining through....

Now to go on further...(hey I had a beer and can't stop typing):)
I still don't have an answer of why I had the idle problem to begin with....remember my idle was perfect until after the first plenum pull. Why did it idle at 900-1100 rpm's after getting into it a little, and not come down to normal when completely stopped until the engine was restarted.....:dontknow: and probably won't know.....the reason being is that I corrected more than one item with the current plenum pull. So I can't say why my idle is perfect now, but am very happy that it is.......lol

Saved you a seat at our Powwow and a piece of fried bread with cinnamon and sugar on top!

We had quite a chat about you the other night at dinner. Don't worry some secrets will never be revealed.....lol...
That fried bread with cinnamon and sugar on it sounds good....I will attend the next Powwow, save me a seat.......:-D

[Roadster]

The degree of wear I have only assumed based on the amount of light shining through on your photos. My secondary blades had nowhere near such amounts of light penetrating at the periphery. My primary however was quite bad.
The original layer of DAG on the TBs was also extremely thin, and not a multiple layer buildup.
Referance photo from ZR1Specialist.com (http://www.zr1specialist.com/HAT%20Web/services/DCP_0875.JPG)

My primary blade has light shinning through it and it should, as if it is completely closed, you will probably have a stalling condition.....
As far as the thin layer of dag, probably was.....but on my TB, it wasn't why, I can't answer that, except that you have to remember that my Z was a "captured test fleet car" that was owned and used by GM engineering for 2 full years. They put 27,000 miles on that vehicle. I am sure that they made adjustments during that time to get the settings where they wanted them to be....I wish I had the file of what when on in those 2 years.....lol
And I still have the prototype PROM chip in my car that was developed by Lotus Engineer Tim Holland for the 93-95 LT5's (also have Marc's chip added):) So I am assuming that my car was a constant test bed during that time....and I am only assuming.......:)

[S.hafsmo]

I agree with the opinion of the DAG application being a band-aid from the factory.
Seems I've missed the fact that the DAG was still there when you first opened the TB. On mine there was nothing left, but that could very well be caused by previous owner maintenance.

A fully sealed primary blade should not cause stalling. If that is the case, the whole TB assembly certainly is a rather poorly constructed device. I've fiddled on a few TBs of that era the last few years, but rarely seen such poor blade fitment as on the LT5.

Kinda cool to have one of the test fleet cars. A piece of history. :)

By the way, did you see the Facebook album posted by one of the engineers behind the original calibration?
https://www.facebook.com/pg/ISJ-Engineering-Ltd-802528229780798/photos/?tab=album&album_id=1460469727319975

One of the comments also lead to an additional album with more photos from the pre-production era.
http://thepandatrap.com/gallery/ZR-1s

http://thepandatrap.com/gallery/var/resizes/ZR-1s/File0063593.JPG