Throttle Body Service
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
Throttle Body Service
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.
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.
Racer
Joined: May 2006
Posts: 283
Likes: 0
From: Pace Florida
perfect timing
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.....
Last edited by Eddywill; Jul 3, 2011 at 04:39 PM.
Burning Brakes
Joined: Feb 2009
Posts: 785
Likes: 3
From: Richmond Virginia
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.....
https://www.corvetteforum.com/techti...=195&TopicID=2
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
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.
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
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?
Burning Brakes
Joined: Jul 2010
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From: When Democracy becomes tyranny, the armed citizens will still get to vote!
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.
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Safety Car
Joined: Sep 2006
Posts: 4,129
Likes: 1
From: Pasadena CA
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
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
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!
I will hafta check that out as the speedo does take a little bit to go to zero.
Thanks guys!
Burning Brakes
Joined: Jul 2010
Posts: 1,210
Likes: 17
From: When Democracy becomes tyranny, the armed citizens will still get to vote!
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.
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
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.
Thread Starter
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
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?
Team Owner
Joined: Jul 2004
Posts: 28,475
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From: Hartford WI
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?
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.
Drifting
Joined: May 2007
Posts: 1,426
Likes: 165
From: Motor City
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.
Last edited by 9T3VETTE; Jul 9, 2011 at 12:18 PM.
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
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 wont if it is bent?? seems odd.
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 wont if it is bent?? seems odd.
Drifting
Joined: May 2007
Posts: 1,426
Likes: 165
From: Motor City
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?
Racer
Joined: May 2006
Posts: 283
Likes: 0
From: Pace Florida
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. 
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
You would read it with a scanner