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Hello guys, I looked for info on this topic and could not find. If I missed it, please point me in correct position. Anyway, I have a 1982 that has a high Idle. When starting cold, it idles around 1400 and then will kick down to 1000ish when warm. In gear it will be roughly 900. I have adjusted the fuel pressure 11.5 psi, balanced the throttle bodies to 6 in of h2o. So it is running really good, just idling high. I also did this. With engine warm and off, I disconnected Rear IAC harness only. Started engine, idle went to 1500, Turned off. Left Rear IAC unplugged and then unplugged front IAC. Idle went to 2000. I turned off, plugged both back in and idle was 750. Thought I had fixed it, by somehow resetting the ECM. Went out today and I am back to 1000ish and 900ish in gear. Idle is smooth and performance is good. I hear that ECM controls idle, so not sure what to do from here. Appreciation in advance.
Hello guys, I looked for info on this topic and could not find. If I missed it, please point me in correct position. Anyway, I have a 1982 that has a high Idle. When starting cold, it idles around 1400 and then will kick down to 1000ish when warm. In gear it will be roughly 900. I have adjusted the fuel pressure 11.5 psi, balanced the throttle bodies to 6 in of h2o. So it is running really good, just idling high. I also did this. With engine warm and off, I disconnected Rear IAC harness only. Started engine, idle went to 1500, Turned off. Left Rear IAC unplugged and then unplugged front IAC. Idle went to 2000. I turned off, plugged both back in and idle was 750. Thought I had fixed it, by somehow resetting the ECM. Went out today and I am back to 1000ish and 900ish in gear. Idle is smooth and performance is good. I hear that ECM controls idle, so not sure what to do from here. Appreciation in advance.
Have you looked in the diagnostic section of the 1982 factory service manual?
I don't have a scanner. Some more info. I took a reading of my TPS at idle. I can not get it lower that 1.2 volts. I have read that it should be .54 V. It does move slowly when I open up throttle plate...... I have also read in another thread to adjust initial idle on rear TB, but I do not see a screw. I only see the screw that adjusts vacuum.
You've got the balancing procedure half-way there (based on what you wrote). Your RPMs could be high due to not setting the TPS after balancing the throttle bodies.
Also, the recommendation for fuel PSI is 13. I have mine set to around 13-15PSI.
While you have got the 6inches (presumably on both sides), that is to set the baseline for air intake. Having it at 6inches will no doubt have you run a high RPM.
The correct procedure for balancing the throttle bodies is as follows:
Warm up to operating temp then turn off.
Disconnect IAC's on both TBs, plug air holes in the throttle bodies
Re-start the engine and put into drive (be sure to chock and set the parking brake)
Using the manometer, verify both throttle bodies are showing 6 inches, if not, adjust throttle stops until 6 inches is achieved.
Make sure to use the middle port on both throttlebodies
be sure to plug the vacuum port for the air cleaner thermac
Once balanced, the rear throttle body (driver side) needs to be adjusted down until the RPMs are at 475 RPM
I would not trust the tachometer on the car, mine shows around 150-200 off. Instead, I got an Innova tach/timing light
Attempted to use WinALDL as well but can't help but feel as though it sets the ECM to a mode that throws off the balancing procedure.
475 is the shop manual rpm. I have mine set to about 550 but looking to bump it up to 650 or so.
Put car into neutral, turn off engine
Use a multi-meter and set the Throttle Position Sensor to +/- 0.525v
If you don't have a connector between the throttle bodies, you can make one for fairly cheap or buy one (Xfire Performance) has them for about $32 + shipping.
Make sure that you check the bottom two pins of the TPS sensor. Anything else will give you an incorrect reading.
Remove plugs from TB's, reconnect IAC's
Restart engine, let run for a few minutes. The RPM's will idle high for a minute or two and then come down.
Take for a drive and get to 35 MPH for a little bit
Alternatively, connect a drill to the speedometer cable and get up to 35 MPH
Last edited by klturi421; Jun 10, 2026 at 08:19 PM.
Thank you klturi421 ! I read the same thing in the Shop Manual. I guess I am scratching my head as to why you adjust the rear throttle body to 6in H20 and then the Front to 6in H20, and then turn the rear down to lower idle. Won't that throw off the balance? I guess intuitively it does not make sense.....Since I have mine balanced at this point (although it was in park), could I not just turn the rear TB screw until I get desired RPM? If it is best, I will do the full procedure....as I am so close and have come so far....why not ??? I love the challenge ! Please advise and thank you.
Thank you klturi421 ! I read the same thing in the Shop Manual. I guess I am scratching my head as to why you adjust the rear throttle body to 6in H20 and then the Front to 6in H20, and then turn the rear down to lower idle. Won't that throw off the balance? I guess intuitively it does not make sense.....Since I have mine balanced at this point (although it was in park), could I not just turn the rear TB screw until I get desired RPM? If it is best, I will do the full procedure....as I am so close and have come so far....why not ??? I love the challenge ! Please advise and thank you.
MK
I honestly have a similar thought as to why 6 but I think it has to do with setting the idle. You get both to 6 to make sure they match, then when you lower the driver's side, the passenger side is lowered as well. Once balanced at 6 and you lower it, it should make sure that the throttle body gets enough air.
I would make sure you're in drive when setting the base RPM. I had it in park when I set it and it throws everything off.
I don't have a scanner. Some more info. I took a reading of my TPS at idle. I can not get it lower that 1.2 volts. I have read that it should be .54 V. It does move slowly when I open up throttle plate...... I have also read in another thread to adjust initial idle on rear TB, but I do not see a screw. I only see the screw that adjusts vacuum.
A scanner is a must have for any fuel injected car. Just by looking at the IAC counts would tell you whether too much air is getting into the engine or the ECM is commanding the high idle speed. Anyhow 1.2 volts could be a bad TPS, out of TPS adjustment range from throttle shaft not fully returning, bad TPS ground. All sensor grounds terminate at the ECM, not chassis ground! It very important not to use chassis ground for sensors. Your FSM will show you where all the screws are and what they do.
Last edited by Fly skids up!; Jun 11, 2026 at 07:22 AM.
Thanks Fly Skip up. I am going to rebalance the TB to 6" as suggested and then turn the Rear one down to get lower idle and then check the TPS voltage. I will keep you guys posted. I appreciate your help.
Ok guys, here's where we are at. I balanced the TB's like the book and Klturi421 suggested. To the book. When I was done, it idled at 600 in Drive and then 700 in park. Check reading on TPS, I couldn't get the TPS to .54. Only .94. I tried all positions. It would go to 4V at WOT. This is with my meter set on DC voltage (9v). Put a dab of epoxy on the passenger screw and let her cure. Started it up today....750. Stepped on gas.....1000. Took it for a drive, about 5 miles. Exactly how it was 900ish in drive, 1000ish in park. One thing I did notice, be a touch disappointed, after I nailed the gas (like lunging) 2-3 times. The idle went down. But in park, you rev it, it goes to 1000. Lunged it again....700. Park rev, 1000. Almost like the throttle plate is not returning 100% every time. Other than that, I am balanced and it runs good. I am going to spray carb cleaner all over tomorrow, maybe my IAC's are leaking or somewhere else.....If not, it runs pretty damn good,,,,going to enjoy it. Bend my tach needle.....LOL
As for the multi meter, 9V setting is almost certainly the incorrect setting. You would probably want 2V or at least 20v (9V is for the 9V battery).
As for the throttle plate not returning, it certainly is a possibility. Once you can accurately measure the TPS you can try moving the throttle manually and let it return and observe the reading on the multi meter, if it changes little bits at a time but is not wildly off, then you likely have a worn throttle shaft (not uncommon for these throttle bodies). I have the same issue with one of the sets of throttle bodies that I have. Looking to have it bushed at some point.
Those throttle shafts on those throttle bodies on notorious for wearing out and causing inconsistent idle. If you have any kind of slop in those shafts you need to rebush the throttle bodies.
OK guys, I watch a very informative youtube video on the use of my multimeter. I am 58 and always wondered what the readings on the meter meant...LOL. I now know. Anyway, This time I checked it the voltage at idle and I am very confident that the lowest I can get the TPS to read is just over 1V. No matter how I move it in the sweep, I can not get lower that 1V. Maybe the arm was bent by PO. I was thinking of removing the TPS and trying to bend the arm in such a way as to be able to get to .5V @ idle, My question is this. What is the ECM looking for? Is it looking for .5V and then it knows the car is at idle and adjusts accordingly? Since mine is 1V, the ECM believes it to be just off idle and makes adjustments and this is why I am at 1000RPM when I am at "idle position"?
OK guys, I watch a very informative youtube video on the use of my multimeter. I am 58 and always wondered what the readings on the meter meant...LOL. I now know. Anyway, This time I checked it the voltage at idle and I am very confident that the lowest I can get the TPS to read is just over 1V. No matter how I move it in the sweep, I can not get lower that 1V. Maybe the arm was bent by PO. I was thinking of removing the TPS and trying to bend the arm in such a way as to be able to get to .5V @ idle, My question is this. What is the ECM looking for? Is it looking for .5V and then it knows the car is at idle and adjusts accordingly? Since mine is 1V, the ECM believes it to be just off idle and makes adjustments and this is why I am at 1000RPM when I am at "idle position"?
It’s possible that the TPS is not good. I wouldn’t bend the arms as that would just be a bandaid and not the solution.
I would pull the TPS off the throttle body, connect the cables (ensure that the multimeter is only on the bottom two of the TPS and test sweeping the arm like that. See if you can get it to read correctly. If it’s not sweeping correctly then it’s possible that the multimeter is still not being properly used or the sensor is bad. If you decide to go with a new sensor, I’d be sure to go with a genuine GM/ACDelco part as I’ve not had good luck using store brand parts. That’s just my experience though.
are you able to share any pics of your set up?
also, here’s a video on how to test the TPS, it’s not the best (also not mine) but it does a decent job of showing where and how to test.
Those throttle shafts on those throttle bodies on notorious for wearing out and causing inconsistent idle. If you have any kind of slop in those shafts you need to rebush the throttle bodies.
Here are pics of the setup. The copper ends you see sticking out are probing the connector. I files the diameter down which you can not see. Even with the TPS completely off, the reading is 1V. It is fully returned at 1V as well. Must be bad?
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1982 High Idle
