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%20W...5%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

[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]

Originally Posted by 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.

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

[Roadster]

Originally Posted by 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%20W...5%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

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...

[Paul Workman]

Originally Posted by Roadster

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...

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).

[Roadster]

Originally Posted by Paul Workman

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).

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]

Originally Posted by Roadster

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

[Roadster]

Originally Posted by Ccmano

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

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.... 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.....

[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]

Originally Posted by 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.

Sounds interesting, can you post pics???