HlhnEast

If you havent serviced your throttle body in a while its time to do it. I just finished up my service to solve a sticky throttle problem and man what a difference it really made. Not only did I solve the sticky throttle, the car doesnt hunt for an idle and settled where it is supposed to. The overall throttle response is incredible.

The process is easy to do. Even with my limited knowledge it was simple enough. There are not many pieces to take apart and the rest is using some TBI cleaner to get the gunk out using a bunch of rags. I was nervous about setting the TPS but it was easier than I thought it would be. All you need is a multimeter that can read the proper voltage.

While you have the TB off, you might want to do a coolant bypass as well. I went a step further and did GREGGPENN's coolant passage elimination to get rid of the bungs and really clean up the TB. It was easy and well worth the effort.

As always I did this with a lot of help from the Forum archives, do a search before you start to get all the info you need.

TWISTERUP

It's always been a very neglected part of maint. on injected cars-Good Job

Eddywill

I just backed my 89 out of the garage for a bath - started it up and it surges while idling - I guess this is what I need to do! Is there a certain how to thread you used or a website? I searched the forum and its all over the place - just being lazy if I need to read them all I will.....

TWISTERUP

From the forum Tech Tips
https://www.corvetteforum.com/techti...=195&TopicID=2

Eddywill

Perfect thank you!

HlhnEast

Thats the archive article I used as a guide to do mine. It was an easy search. For narrower results click "advanced search" then select the specific forum after loading the search terms.

HlhnEast

The TB still takes a bit for the idle to come down from 1000-1200 after stopping at a light or similar. Anyone got an idea why or is this common? Do I need a new throttle return spring?

cadwiz_01Z

If it is anything like mine, there is a little extra clearance/wear in the rod that everything is mounted to. This doesn't let it close correctly. I usually have to blip the throttle to get it to idle down when I come to a stop.

Eakster

On my 96 at least it's directly linked to the speedo. The electronic speedo on these cars is pretty slow to react. I often watch it count down after I've come to a complete stop. You won't get normal idle until that speed reading says exactly 0

aklim

Check the IAC counts. Was it adjusted right

HlhnEast

Since I dont know what your talking about I guess not. What exactly is IAC counts and how is it adjusted. The IAC I installed was one I had laying around as I broke the original one. The idle was doing the same thing before I switched it out tho.

I will hafta check that out as the speedo does take a little bit to go to zero.

I guess the only solution there is to buy a new TB?

Thanks guys!

cadwiz_01Z

You'll have to search for the exact sequence to reset the IAC. I found it on here somewhere. It seems like depressing the gas pedal and cranking, then off and back on within a few seconds, or something like that. It's been a while since I did it on my 89.

aklim

IAC is the Idle Air Control. It is a metered air leak. It is used to control idle speed. If it wants to raise idle speed, it will retract the pintle and thus let more air in. Lower idle speed, the reverse. Obviously you will need a scanner to do it.

This is how I like to do it. Shut of everything except the engine which is in closed loop. Hook up a scanner and see how many counts you have. Target is about 20 counts. If it is more, turn in the screw. Rev the motor. Recheck. If it is lower, turn out the screw.

You can't be really sure what the IAC is doing just by looking at the tach.

HlhnEast

Thanks! I understand what the IAC does and how it operates but didnt know how to adjust anything on it. I see that the plunger dealie can be screwed in and out. Is it where the IAC plunger is closing slowly that delays the idle from settling? Does the IAC count determine this?

aklim

The plunger is screwed in because it might be too extended for the unit to seal properly. Other than that, don't adjust it, you could break it. Ask my friend how.

The IAC count is the ECM telling you how much it has to be adjusted. So if you have a target of 20 counts and you achieve it, great. Say you turn the AC on and it needs more engine speed to compensate, the ECM commands more IAC and the pintle retracts to allow more air to pass thru the "leak". This raises the RPM and reads as say 40 counts. When it needs less air, it extends the IAC and you see it as say 10 counts.

9T3VETTE

Not to hijack your thread, but I think we are all having similar issues.

I'm also chasing this problem down too. Cold starts are fine (idles ~650). Once the engine warms up after a bit of driving and I come to a stoplight (in neutral position) the idle is around 1,000rpm or even sometimes on a hot day around 1,200rpm.

Once i come to a complete stop it will come down a bit, but still above the normal idle condition. Like cadwiz said, it usually takes a blip of the throttle to bring it down.

Yesterday when i came home it was idling high, I got out and checked the throttle cable. There seemed to be slack in the cable but i was able to press on the throttle cable bracket and the idle went down.

I wonder if it is bent?? seems odd.

aklim

Has the TB and the IAC housing been cleaned lately? Have you checked for leaks around all the hoses? I had that same issue when the IAC wasn't adjusted right

9T3VETTE

The throttle body was off last weekend to get cleaned as well as the IAC. Also, I followed the FSM procedure to reset the position of the IAC. It could possibly need to be replaced but I kind of doubt it. Need to check my counts but not sure how to do so?

Eddywill

I cleaned the throttle body and IAC unit and put it back on. What a mess to it was (the build up not the job). Started right up and idled fine..... Then a few hours later fired it up and it started searching for idle again.... Not as bad as before but its not a smooth idle.

aklim

You would read it with a scanner