IAC question...

[Ccmano]

So the idle speed on the Z is a bit high by about 2-300 rpm. I've gone after potential vacuum leaks and I think I have addressed all of them. The IAC readings on my Tech1 are 0 at idle, indicating there is still an issue. In researching this I came accross Haibecks presentation on the issue. One of the items on his list is the IAC stepper motor. His test is to remove the motor, remove the o-ring and reinsert it into the throttle body. He says there should be a .020 gap between the TB and the motor body. Indicating that the pintle of the motor is seated against the TB, sealing it up properly.

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

I checked the old one and found I had zero gap. So I picked up new one today from Summit. Even made sure the part numbers cross referenced. Darned if it doesn't do the exact same thing. No gap!

Has anyone run accross this? Does the 90' have a different IAC motor?

TIA
H
:cheers:

[S.hafsmo]

My 90 had a slight gap. Don't know if they are 100% closed when de-energized, but to make sure mine was in fully closed position, I started the car, pulled off one of vac hoses on the plenum (causing idle to increase and IAC to compensate), and disconnected the harness from the IAC, hopefully "locking it" in closed position. Then stopped the car and did the gap test.

Worn throttle blades seem to be the most popular cause of high idle these days.

[Ccmano]

My 90 had a slight gap. Don't know if they are 100% closed when de-energized, but to make sure mine was in fully closed position, I started the car, pulled off one of vac hoses on the plenum (causing idle to increase and IAC to compensate), and disconnected the harness from the IAC, hopefully "locking it" in closed position. Then stopped the car and did the gap test.

Worn throttle blades seem to be the most popular cause of high idle these days.

Interesting, I'll give it a shot.

I've following the adventures of Roadster. Hope it doesn't come the that! After reading that it might just be easier the burnish the throttle Plates and do a custom fit.
H
:cheers:

[Roadster]

So the idle speed on the Z is a bit high by about 2-300 rpm. I've gone after potential vacuum leaks and I think I have addressed all of them. The IAC readings on my Tech1 are 0 at idle, indicating there is still an issue. In researching this I came accross Haibecks presentation on the issue. One of the items on his list is the IAC stepper motor. His test is to remove the motor, remove the o-ring and reinsert it into the throttle body. He says there should be a .020 gap between the TB and the motor body. Indicating that the pintle of the motor is seated against the TB, sealing it up properly.

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

I checked the old one and found I had zero gap. So I picked up new one today from Summit. Even made sure the part numbers cross referenced. Darned if it doesn't do the exact same thing. No gap!

Has anyone run accross this? Does the 90' have a different IAC motor?

TIA
H
:cheers:

Not to say I have the solution to your idle problem, but this is what I ended up doing...
I did not actually check the gap this particular time when I installed the IAC. I did however make sure that the pintle was under an inch from the base by depressing it by hand as shown in the pic as per FSM instructions below.

the instructions as per FSM...
"Tighten to 27 lb. in.
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"

Also as has been mentioned, you would need to adjust your min-air screw and turn it counter clock wise to bring up your IAC counts. And you only turn that screw one "hair" at a time. Just a very, very slight touch is all that is needed. Then blip the throttle, and let the idle settle down and then check and reset your TPS if needed, blip the throttle again and let the idle settle down. You may have to repeat this procedure to get your readings within range. I would recommend a test drive after each of the two adjustments with your Tech 1 connected.
And of course these adjustments are made with the engine fully warmed up and in Closed Loop, which you probably know.
If your idle is still the 200-300 rpm's higher that you mentioned, there you most likely have another issue that needs to be determined and addressed.
BTW, what is your idle reading at now???
Good luck, hope you get everything corrected....


the pintle after retraction...I know the tape measure is not flush against the base, but placed it there to give you an idea....the pintle is now under one inch when adjusting the tape measure for the difference...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170419_001242.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170419_001242.jpg.html)

[Paul Workman]

Not to say I have the solution to your idle problem, but this is what I ended up doing...
I did not actually check the gap this particular time when I installed the IAC. I did however make sure that the pintle was under an inch from the base by depressing it by hand as shown in the pic as per FSM instructions below.

the instructions as per FSM...
"Tighten to 27 lb. in.
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"

Also as has been mentioned, you would need to adjust your min-air screw and turn it counter clock wise to bring up your IAC counts. And you only turn that screw one "hair" at a time. Just a very, very slight touch is all that is needed. Then blip the throttle, and let the idle settle down and then check and reset your TPS if needed, blip the throttle again and let the idle settle down. You may have to repeat this procedure to get your readings within range. I would recommend a test drive after each of the two adjustments with your Tech 1 connected.
And of course these adjustments are made with the engine fully warmed up and in Closed Loop, which you probably know.
If your idle is still the 200-300 rpm's that you mentioned, there you most likely have another issue that needs to be determined and addressed.
BTW, what is your idle reading at now???
Good luck, hope you get everything corrected....


the pintle after retraction...I know the tape measure is not flush against the base, but placed it there to give you an idea....the pintle is now under one inch when adjusting the tape measure for the difference...
http://i127.photobucket.com/albums/p138/SSROADSTER/94%20ZR-1/20170419_001242.jpg (http://s127.photobucket.com/user/SSROADSTER/media/94%20ZR-1/20170419_001242.jpg.html)

Interesting. I was unaware that blipping the throttle would reset the IAC after making the adjustment(s). Rather, I turned the ignition OFF for a few seconds, and then restarted. Hmmmm....

Also, I found the number of iterative procedures (adjusting the idle air screw and then the TPS voltage) was effectively cropped by adjusting the TPS first before turning the ignition off (or perhaps "blipping" would be easier!) to reset the IAC counts.

Anywayz...thanks for the tip. If ever I have a need to adjust the IAC again, I'll give "blipping" a try (as opposed to the OFF, re-start routine).:thumbsup:

:happy1:

[Roadster]

Interesting. I was unaware that blipping the throttle would reset the IAC after making the adjustment(s). Rather, I turned the ignition OFF for a few seconds, and then restarted. Hmmmm....

Also, I found the number of iterative procedures (adjusting the idle air screw and then the TPS voltage) was effectively cropped by adjusting the TPS first before turning the ignition off (or perhaps "blipping" would be easier!) to reset the IAC counts.

Anywayz...thanks for the tip. If ever I have a need to adjust the IAC again, I'll give "blipping" a try (as opposed to the OFF, re-start routine).:thumbsup:

:happy1:

Paul, I guess at times I do things unconventional....lol
As when I adjusted the min-air screw, both times I did it with the engine off. What I did was use a black marker to make a line on the side of the hex bolt as a reference to make sure I only turned it just a "hair"....lol
I then started the engine and let the idle settle down, blipped the throttle again and then checked the TPS, which at times I did adjust with both the engine running and not running. So far, so good.....:)

[Ccmano]

BTW, what is your idle reading at now???
Good luck, hope you get everything corrected....


Roadster, after your recent adventures you may be the resident expert on this subject. Good info, I will go back through and re-evaluate. My idle is currently running 950-1050. As was yours, when first starting the car from cold and the throttle untouched it will settle in to about 750ish. But once driven it will not go below 950.
Thanks
H
:cheers:

[Roadster]

Roadster, after your recent adventures you may be the resident expert on this subject. Good info, I will go back through and re-evaluate. My idle is currently running 950-1050. As was yours, when first starting the car from cold and the throttle untouched it will settle in to about 750ish. But once driven it will not go below 950.
Thanks
H
:cheers:

Not an expert by any stretch, but thank you for the compliment.:)
You also have to remember (as you were following my thread) I did a number of other items which may have helped with my idle problem.....
such as....
1-checked for vacuum leaks
2-replaced the rubber connector under the plenum for the canister line
3-replaced #8 spark plug wire, as it was not giving me an ohm reading and was corroded in the plug end
4-repaired #7 spark plug wire at the coil tower end, as it would not make a secure contact, and would pop up slightly when attaching.. A squeeze with the pliers on the outside of the boot corrected that problem
5-and the now "famous dag" application after I completely cleaned the inside of the TB which your not supposed to do....[-X:redface: but I figured I take a chance and get to learn something in the process. As I have mentioned, to seal your secondary blades with the "dag" takes a lot of time and patience to make sure the blades are sealed in the bores when in the closed position. It took many applications (some minor) to fill in the gaps. I think I accomplished that, but I feel I also got lucky as it has worked out for me...

So I can't really state what corrected my idle problem as when each item was completed it was not tested until everything was done. Looking at it from a logical standpoint, I would probably have to say that the "dag" application played a role in correcting my problem. But then again, my secondary blades were pretty sealed from the original "dag" from the factory. So I really can't point to one correction that made the difference, but whatever is was, is now working....
Again, I hope you get squared away....looking forward to your results.....:-D

[mike100]

I never posted much on the subject, but after fixing all the stuff under the plenum, I assumed that i had some throttle plate leakage that wasn't worth fixing. what I did was include a restricted pipe in the pvc to the throttle body inlet tube that runs along the left cam cover. So as to have full ventilation on the pvc pipe, I T'd another vacuum tube to an atmospheric vent filter...like one of theose k&n type mini filters you see on valve covers.

I could always have 15-20 counts on the IAC reading on my Tech1. this pretty much allowed the target idle to be satisfied also. Of course i hid the tee'd vacuum circuit for emissions testing, but that was pretty easy.

[Roadster]

I never posted much on the subject, but after fixing all the stuff under the plenum, I assumed that i had some throttle plate leakage that wasn't worth fixing. what I did was include a restricted pipe in the pvc to the throttle body inlet tube that runs along the left cam cover. So as to have full ventilation on the pvc pipe, I T'd another vacuum tube to an atmospheric vent filter...like one of theose k&n type mini filters you see on valve covers.

I could always have 15-20 counts on the IAC reading on my Tech1. this pretty much allowed the target idle to be satisfied also. Of course i hid the tee'd vacuum circuit for emissions testing, but that was pretty easy.

Sounds interesting, can you post pics???

[XfireZ51]

Roadster, after your recent adventures you may be the resident expert on this subject. Good info, I will go back through and re-evaluate. My idle is currently running 950-1050. As was yours, when first starting the car from cold and the throttle untouched it will settle in to about 750ish. But once driven it will not go below 950.
Thanks
H
:cheers:

Hans,

Of course if IAC is at 0, then u have a vacuum leak but that could be at primary throttle blade. I posted a procedure for adjusting Min Air a few months ago.
Basically u want motor to idle at just below ur target w minimal IAC intervention
ie 10-15 steps. TPS V will need to be adjusted after each change.

[Ccmano]

Dom,

I'd did the reset of the IAC motor today with no improvement. I saw your post on the Min Air Adj., that's up next. Good write up! I'll keep you posted.
H
:cheers:

[Hib Halverson]

Do not change the minimum air adjustment. That's a bandaid fix. You've replaced the IAC motor so you know that's not the issue. The engine ran ok at some time in the past with the existing min. air setting, so that's not an issue.

The only time IAC counts go to zero and stay there is if you have air entering the engine other than through the TB.

This can be "vacuum leaks", worn TB, primary throttle blade not returning to closed position or, maybe, wrong PCV valves.

[Ccmano]

So... I pulled the TB and it appears the issue was a combination of a sticky primary throttle plate and air leakage past the secondary Plates to a small degree. I converted the min air adjustment screw a bolt head type with counter nut. Verified all the related potential vacuum leak hoses and replaced a few. Added new TB gaskets from Jerry's (thank you as always).

Put it all back together and did the min air adjustment setting per Dom & Pauls instructions. Idle is now ~750 right at target. IAC's are running ~6 and throttle position voltage is 0.54volts. Turn the a/c on and IAC's jump to ~35 and maintain idle at ~750. A/C off and it all settles back to normal.

Operation a success!

Headers, exhaust, clutch, flywheel and engine mounts are next....:dancing

Thanks to all.
H
:cheers:

[XfireZ51]

Hans,

U may find a bit crisper throttle response.

[Ccmano]

Hans,

U may find a bit crisper throttle response.

I did actually notice that on the test drive afterwards. When the Fidanza goes in I expect further enhancement to throttle response.
H

[tpepmeie]

Hans,

U may find a bit crisper throttle response.

Dom,
why would that be?

[XfireZ51]

Dom,
why would that be?

Less bypass air. Mire air going thru throttle blade, better velocity.

[Paul Workman]

Less bypass air. Mire air going thru throttle blade, better velocity.

I agree - the throttle is crisper; no doubt on that. But, ya lost me on the "why" of it, unless you're throwing CAMS into the mix as well.

More air going through the throttle blades is a function of lower IAC counts...which were likely set after installing bigger cams, yes? And, as for velocity...you'll have to "splain it Lucy!":icon_scra

I think the response crispness comes from (according to the FSM) the ~ .4 seconds for the SPT system to fully comply with the "ON" signal, but only in certain situations.

In normal driving i.e., the throttle is opened more or less gradually and the SPTs are activated w/o the driver being conscience of when the .4 second lag interval began. Therefore, the response time isn't relevant (or even noticed?). But! If any time the throttles are snapped to WOT, in anticipation of an immediate and FULL POWER ON response from the motor - and the quicker the better - .4 seconds lag seems like an eternity, especially when at the drag strip that guy in the adjacent lane has jumped a car length on ya!

Well, whatever the reason, the crispness IS there (the FSM says so!), and if one has an aluminum FW, the "seat-o-the-pants" meter will definitely agree every time the the throttle is whacked!:dancing

[XfireZ51]

Paul,

The crispness of the throttle or the sensitivity of the throttle to changes is not dependent on the SPT opening or closing. I'm describing what I feel even at minute throttle changes, cams or no cams. I have done that for both configurations. The IAC position is dependent on throttle opening not the other way around. There are delays and filters for IAC opening and closing that follow the throttle position.
When tuning, the objective is to minimize the ECM intervention. Prior to computerized engine management, u tuned a carb to maximize vacuum. Same concept w Min Air Adjustment except that u DO want to leave some margin for the IAC to intervene in cases such as coast down or sudden throttle closing.
In a tuning strategy, u limit the amount of IAC steps for part throttle but maximize it for WOT to get as much air as possible. So better response botom to mid range, top end more air. Can also use the delays as a means of controlling rpm drop when shifting.
When the secondaries are disabled, I eliminate the delay in the calibration.

[Paul Workman]

Paul,

The crispness of the throttle or the sensitivity of the throttle to changes is not dependent on the SPT opening or closing. I'm describing what I feel even at minute throttle changes, cams or no cams. I have done that for both configurations. The IAC position is dependent on throttle opening not the other way around. There are delays and filters for IAC opening and closing that follow the throttle position.
When tuning, the objective is to minimize the ECM intervention. Prior to computerized engine management, u tuned a carb to maximize vacuum. Same concept w Min Air Adjustment except that u DO want to leave some margin for the IAC to intervene in cases such as coast down or sudden throttle closing.
In a tuning strategy, u limit the amount of IAC steps for part throttle but maximize it for WOT to get as much air as possible. So better response botom to mid range, top end more air. Can also use the delays as a means of controlling rpm drop when shifting.
When the secondaries are disabled, I eliminate the delay in the calibration.

Ah! Gotcha, Dom. I think we're in "violent agreement" - for the most part (including the IAC setting vs. idle air adjustment - I meant to say that the process is iterative, but to be clearer, the throttle air set screw is adjusted, then the TPS voltage optimized, and then the IAC counts are checked to see what the net effect of the idle air screw was...if that clears it up?)

However, I don't think you meant to imply the SPT actuators don't affect the throttle response (on a stock motor). In fact, as you know, there is a mechanical delay (the SPTs don't open instantly!), and because of that, a necessary interim injector delay is programmed in the calibration. So, the net result, as anyone with the secondary delete mod may know, both of these delays are eliminated/moot, resulting in a very crisp response to (WOT) changes...I think is the point.:)