Hunting idle issue

[MuRCieLaGo]

Hello guys,

Today is a good day. Been searching for a long time for my low RPM bucking issues (especially when warm).

Changed o2 sensors, fuel filter, fuel pumps, spark plugs, spark plug wires, cam sensor, battery... All without success.

Today, I changed the coil packs. It seems to have fixed the problem. The car was running fine at high RPM, I still don't understand!

Anyway, it brought a new problem. I've got slightly high and hunting idle now. As you can see in the video, nobody touched the gas pedal on throttle cable and it went all the way from 800 RPM to 1,900 RPM all of a sudden.

https://www.youtube.com/watch?v=Jr7QD11eJzs

I've got no clue what it could be.

Any ideas?

Thanks!

[Ccmano]

A hunting idle is almost always a vacuum leak. No magic bullet for that. Just a matter of going through and checking and eliminating the various vacuum systems.
H
:cheers:

[Billy Mild]

Vacuum leak. Make sure everything is ZIPtied or RTV'd to seal up any leaks. Outside of that if that all checks out then place a book in front of the airhorn. If the idle drops down then that is your issue. The TB sticks.

On the point of getting the Vacuum leaks fixed make sure to use a mityvac on each connection with the manifold on to see where its leaking at. The MityVac really helps pinpoint this stuff.

[GOLDCYLON]

Vacuum leak X3

[XfireZ51]

When you swapped coil packs, did you disconnect throttle cable when removing plenum?

[MuRCieLaGo]

Vaccuum leak - I'll double check...

But personally I think XfireZ51 is closer to finding the problem.

When I disconnected both cables, I heard a weird sound from the system - like if I broke something... Couldn't see anything obvious though.

In the video, you can see that it went from 800 RPM to 1,900 RPM pretty fast. A raise to RPM due to vaccuum leak would be much slower, no?

By the way, thanks a lot for your help guys. I bought a Viper 1994 and the forums are pretty bad. People are being sarcastic and think they own a Ferrari. I love this forum here.

[MuRCieLaGo]

I just started it at a pretty cold weather and I had a rock solid idle at 1,500RPM...

[Ccmano]

What year is the car?
H

[MuRCieLaGo]

1991

[Ccmano]

So we can count out the ASR adjuster cable, 90’s and 91’s didn’t have ASR. Check the throttle and cruise control cables, there should not be any tension on them at idle. Just a very small (tiny) amount of slack.

Make sure there is nothing interfering with the throttle linkage assembly to hold it slightly open. That assembly where the throttle cables hook into.

If you find that the throttle linkage is fully at rest when idling we have to look elsewhere.

The IAC motor is another possibility. It was no doubt disconnected when the plenum was off. Try resetting it. #4 post in the following thread.
http://www.zr1.net/forum/showthread.php?t=28178&highlight=IAC+reset

I still strongly suspect a vacuum leak somewhere.
H
:cheers:

[MuRCieLaGo]

I like the idea of resetting that IAC. Thanks a lot for your detailed answer, will continue my homework ASAP!

[XfireZ51]

Disconnecting the throttle cables necessitates re-doing the Min Air Adjustment.
That’s why I remove my plenum w throttle cables attached unless absolutely necessary otherwise.
The idle oscillation can also be a result of the throttle plate being open beyond the idle setting. Check ur TPS v and adjust if needed.

[Ccmano]

Disconnecting the throttle cables necessitates re-doing the Min Air Adjustment.
That’s why I remove my plenum w throttle cables attached unless absolutely necessary otherwise.
The idle oscillation can also be a result of the throttle plate being open beyond the idle setting. Check ur TPS v and adjust if needed.

Some good points, was the throttle position sensor removed or possibly knocked out of adjustment? Good to check the voltage.

With regard to a vacuum leak, while there are many possibilities, how much is your vacuum pump running with the ignition on but engine not running?
H
:cheers:

[secondchance]

Some good points, was the throttle position sensor removed or possibly knocked out of adjustment? Good to check the voltage.

With regard to a vacuum leak, while there are many possibilities, how much is your vacuum pump running with the ignition on but engine not running?
H
:cheers:

If the pump stays quiet for 45 seconds, it's acceptable. However, this means good vacuum up to check valve. There could be other vacuum leak into intake.

[MuRCieLaGo]

Tonight I checked some stuff.

-No obvious leak.
-Vaccuum pump stays quiet for 13 seconds.
-TPS checked: 0.55V.
-Throttle cable isn't too tight, there's a slight slack in it when at rest.
-Tried to reset IAC, procedures don't seem to do anything.

Still no success...

When I let the car coast in 2nd gear I'm at 18 mph!

[Ccmano]

Tonight I checked some stuff.

-No obvious leak.
-Vaccuum pump stays quiet for 13 seconds.
-TPS checked: 0.55V.
-Throttle cable isn't too tight, there's a slight slack in it when at rest.
-Tried to reset IAC, procedures don't seem to do anything.

Still no success...

When I let the car coast in 2nd gear I'm at 18 mph!

Ok, as Haibeck says (and I believe Hib too)... high idle is caused by a vacuum leak 99% of the time. In my opinion messing with the “min air adjustment” is a last resort and you need at least a Tech 1 scanner to do it. For your idle to change suddenly after a plenum pull still indicates a leak. The only way I would suspect the throttle body (requiring a min air adjustment) is if you wiped away the DAG sealing compound around the secondary throttle Plates thinking it was dirt build up. Another member here had fun with that one.

I would start here with Haibecks write up.

http://www.zr1specialist.com/HAT%20Web/articles/Finding%20and%20Fixing%20Vacuum%20Leaks%20on%20the %20LT5%20Engine.pdf

H
:cheers:

[Hib Halverson]

If your secondary vacuum pump runs every 13 seconds you likely have a small leak somwhere in the SPT vacuum system.

However, as others have suggested if you have a vacuum leak which is causing the idle speed problem, it's not a leak in the SPT system causing the trouble.

If you can't find a leak, then maybe the TB is worn out and leaking.

In any event, fooling with minimum air to solve your problem is not a wise idea.

Marc's discussion of vac. leaks is outstanding. Like others suggest, start by reading that.

[XfireZ51]

Just to set the record straight, nobody is suggesting that Murcielago’s issue would be remedied by resetting the Min Air. Whenever addressing issues like this my approach is to first confirm that the basic settings and parameters are within spec. And that’s ALL I was recommending.
However, I would suggest getting a scantool (don’t need a Tech 1), to look at IAC COUNTS. You should have one anyway. It pays for itself many times over IMO.

[XfireZ51]

What was the coolant temp that video was shot at? Just after startup?

[MuRCieLaGo]

So I guess I'll go through that pdf, seems to be fairly simple! I bought a Bluetooth adapter but it doesn't work in real time, I get a reading every 3 seconds when I'm lucky (frustrating). I might remove that Secondary Vaccuum System (and sending my chip to Marc Haibeck)...

Video was taken at the startup after disconnecting the battery. Temperature was just starting to rise on the needle (10 minutes after I started the car).

PS: When I removed the plenum, there was still some pressure in the coolant system. I know it basically filled the hole that goes to #6 cylinder. The car had a lot of white smoke for maybe 15 minutes at idle. Not sure if it could have affected something.

I can't thank you enough for your help guys. I love the ZR-1 community, so friendly.

[Ccmano]

So I guess I'll go through that pdf, seems to be fairly simple! I bought a Bluetooth adapter but it doesn't work in real time, I get a reading every 3 seconds when I'm lucky (frustrating). I might remove that Secondary Vaccuum System (and sending my chip to Marc Haibeck)...

Video was taken at the startup after disconnecting the battery. Temperature was just starting to rise on the needle (10 minutes after I started the car).

PS: When I removed the plenum, there was still some pressure in the coolant system. I know it basically filled the hole that goes to #6 cylinder. The car had a lot of white smoke for maybe 15 minutes at idle. Not sure if it could have affected something.

I can't thank you enough for your help guys. I love the ZR-1 community, so friendly.

As Hib states a small leak in the secondary system is unlikely to cause the idle problem. When you took the plenum off the last time what exactly did you do besides the coil packs? If you removed the injectors and the fuel rail it possible your vacuum leak is at one of the injector O rings.
H
:cheers:

[MuRCieLaGo]

As Hib states a small leak in the secondary system is unlikely to cause the idle problem. When you took the plenum off the last time what exactly did you do besides the coil packs? If you removed the injectors and the fuel rail it possible your vacuum leak is at one of the injector O rings.
H
:cheers:

I didn't touch anything from the fuel system. But I do hear an "air sound" from somewhere under the plenum, driver's side. Can't see anything disconnected though.

Got called today to work on a ship until January.

To be continued in 2018!

[XfireZ51]

I didn't touch anything from the fuel system. But I do hear an "air sound" from somewhere under the plenum, driver's side. Can't see anything disconnected though.

Got called today to work on a ship until January.

To be continued in 2018!

Must be a significant leak if u can hear it w motor running.

[Ccmano]

Bingo....
H

[XfireZ51]

So blocking the airhorn should make it even louder.

[tiegsd]

MAP sensor line disconnected or clogged maybe?

Sent from my SM-N920V using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[MuRCieLaGo]

So blocking the airhorn should make it even louder.

I'll try this!

MAP sensor line disconnected or clogged maybe?

Sent from my SM-N920V using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

Car pulls perfectly strong... If the line was disconnected/clogged, the car would have lots of black smoke and run really bad, if I'm not mistaken.

[tiegsd]

Hmmm, yeah it was the hunting that made me think of this, super easy to check. Car ran like crap at in town speeds, but seemed to smooth out when I got on the throttle. Anyway, just a thought.

Sent from my SM-N920V using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[MuRCieLaGo]

I've got another question that might be related to the issue...

If somebody can answer that, he will be my new hero.

In June, I also removed the plenum. When I removed the hose pictured, look what I found inside the hose. What is that?

https://scontent-ort2-1.xx.fbcdn.net/v/t1.0-9/23722450_10159992330050221_6855549723905347024_n.j pg?oh=5581ec1bcd3d785618cbb47d939b3559&oe=5A8922A9

https://scontent-ort2-1.xx.fbcdn.net/v/t1.0-9/23659603_10159992330025221_976599702637979565_n.jp g?oh=0e3eba132fe58d3c97edebe0d0ab4331&oe=5A909E44

[XfireZ51]

If it was in the fuel pressure regulator hose, it should not have been. It was blocking vacuum to the FPR and so not allowing correct fuel pressure.

Question is why would someone do that?

[MuRCieLaGo]

If it was in the fuel pressure regulator hose, it should not have been. It was blocking vacuum to the FPR and so not allowing correct fuel pressure.

Question is why would someone do that?

So you're saying I should have left it there? I just threw it away... I don't get it. Could it be related to my issue? Do you think I can get another one at the dealership, or somewhere else?

[A26B]

So you're saying I should have left it there? I just threw it away... I don't get it. Could it be related to my issue? Do you think I can get another one at the dealership, or somewhere else?



This was someone’s idea of how to increase fuel pressure, by blocking the fuel pressure regulator vacuum source. Probably thought it might result in more power.
Toss the foreign piece & reinstall the vacuum hose.


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[XfireZ51]

By blocking the plenum vacuum to the FPR, fuel flow would be inconsistent throughout the range of engine vacuum resulting in either too much or too little fuel.

[MuRCieLaGo]

Alright! I don't like to see that kind of stuff on my car. I hope I won't find other stupid mods like this!

Thanks guys!

[jss06c6]

What the hell?? Sabotage?? No rational reason unless some other means of fuel management is installed.

Sent from my XT1585 using ZR-1 Net Registry mobile app (http://r.tapatalk.com/byo?rid=90383)

[MuRCieLaGo]

Ok, as Haibeck says (and I believe Hib too)... high idle is caused by a vacuum leak 99% of the time. In my opinion messing with the “min air adjustment” is a last resort and you need at least a Tech 1 scanner to do it. For your idle to change suddenly after a plenum pull still indicates a leak. The only way I would suspect the throttle body (requiring a min air adjustment) is if you wiped away the DAG sealing compound around the secondary throttle Plates thinking it was dirt build up. Another member here had fun with that one.

I would start here with Haibecks write up.

http://www.zr1specialist.com/HAT%20Web/articles/Finding%20and%20Fixing%20Vacuum%20Leaks%20on%20the %20LT5%20Engine.pdf

H
:cheers:

WAIT!

is if you wiped away the DAG sealing compound around the secondary throttle Plates thinking it was dirt build up

I did that! I removed that plate because I thought I had to remove the plate to remove the plenum. The gasket there was super-worn and there was some coolant coming out of there if I remember. Could this faulty gasket cause all that mess? Hopefully Jerry sells it!

[XfireZ51]

WAIT!

is if you wiped away the DAG sealing compound around the secondary throttle Plates thinking it was dirt build up

I did that! I removed that plate because I thought I had to remove the plate to remove the plenum. The gasket there was super-worn and there was some coolant coming out of there if I remember. Could this faulty gasket cause all that mess? Hopefully Jerry sells it!

Once u have removed the throttle plate, its difficult to get it properly seated again in the venturi. Ask me how I know. Finally sent the throttle body to Marc to have the TPs correctly positioned in the throttle bores.

If you meant “throttle body” and not throttle plate, disregard above.

[MuRCieLaGo]

Once u have removed the throttle plate, its difficult to get it properly seated again in the venturi. Ask me how I know. Finally sent the throttle body to Marc to have the TPs correctly positioned in the throttle bores.

If you meant “throttle body” and not throttle plate, disregard above.

I meant #39 (in bold). That gasket is probably not sealing anymore. I wonder if it is what Ccmano meant.

I already ordered the gasket via Jerry's website but I wonder if it'll fix my problem.

https://image.ibb.co/gjoPYS/29133723_10160503093780221_5722408541638098944_n.j pg

[XfireZ51]

If I read this right, that gasket is for the coolant crossover in the throttle body.

[Ccmano]

The DAG is inside the throttle bores sealing the throttle Plates when closed. If you extend the line at #10 into the throttle bore, thats what I mean.
H
:cheers:

[MuRCieLaGo]

Oh... You just ruined my evening. I'll keep searching then.

[MuRCieLaGo]

I'm wondering if that "air" sound is normal. It's pretty loud.

https://youtu.be/yMQEB8fUhXE

[Ccmano]

Can’t tell from the video. There’s a leak somewhere just keep at it.
H
:cheers:

[MuRCieLaGo]

Can’t tell from the video. There’s a leak somewhere just keep at it.
H
:cheers:

Sorry I didn't update the thread.

I feel bad. 5 pages... Maybe I should type less and work more.

Problem was pretty much impossible to see with the plenum still on... But when I removed it, it was pretty simple. Marc Haibeck says on his awesome vacuum leaks PDF that GM added a clamp on that "rubber connector" after '91. However, I went to get the part number of that clamp to GM and they showed me the diagram of a '92.

There is no clamp.

https://image.ibb.co/gKe3FH/29216367_10160518851085221_1976158626628239360_n.j pg

Anyway, problem seems to be solved now. However, vacuum pump still turns on every 15 seconds or so. Haven't really tested the car on the road, it's winter here.

[XfireZ51]

This is a major reason of why we dump the secondaries. Besides, there's better use for that vacuum.

[Ccmano]

Pump running every 15 seconds is fine. Haibeck says if it stops for at least a second or two there is enough vacuum back up. Good work tracking it down!
H
:cheers:

[MuRCieLaGo]

This is a major reason of why we dump the secondaries. Besides, there's better use for that vacuum.

That was my plan initially but when I found out that you need to access the heads (or something like that, I can't remember), I gave up that project.

Pump running every 15 seconds is fine. Haibeck says if it stops for at least a second or two there is enough vacuum back up. Good work tracking it down!
H
:cheers:

Thanks you've all been very helpful I'll remember that!

I'm on the forums for 4 sports cars and this one here is the best, no doubt!

[XfireZ51]

That was my plan initially but when I found out that you need to access the heads (or something like that, I can't remember), I gave up that project.



Thanks you've all been very helpful I'll remember that!

I'm on the forums for 4 sports cars and this one here is the best, no doubt!

You can just tie-wrap the secondaries OPEN and get a calibration supporting that.

[MuRCieLaGo]

You can just tie-wrap the secondaries OPEN and get a calibration supporting that.

If I am to delete the system, I'd rather do it cleanly and remove it completely!