quick idle question
Thread Starter
Burning Brakes
Joined: Jun 2016
Posts: 1,052
Likes: 101
From: Ohio
quick idle question
hey everyone -
my idle on my 85 4+3 seems a little high - in the garage it stays around 7-800 in neutral - but the last couple of drives had it closer to 1-1100 in neutral at lights. temp was around 160-170 and everything seemed ok. I did clean the tb before and change the iac checked for vac with vac gauge and it was within "normal" engine range on the gauge. I was going to check the tps and was following the "check codes" by corvette Ben - the only code mine would register was 12. is there more to code 12? is there something else I should check? or something else I should do with the iac - reset? or will it finally reset itself after a while
thanks
Sean
my idle on my 85 4+3 seems a little high - in the garage it stays around 7-800 in neutral - but the last couple of drives had it closer to 1-1100 in neutral at lights. temp was around 160-170 and everything seemed ok. I did clean the tb before and change the iac checked for vac with vac gauge and it was within "normal" engine range on the gauge. I was going to check the tps and was following the "check codes" by corvette Ben - the only code mine would register was 12. is there more to code 12? is there something else I should check? or something else I should do with the iac - reset? or will it finally reset itself after a while
thanks
Sean
Racer
Joined: Mar 2020
Posts: 384
Likes: 144
From: Langton, Ontario, Canada
2025 C4 of the Year Finalist - Unmodified
12 is the code that flashes first, before "meaningful" codes. Think of it as a filler, before and after all the real codes.
It means nothing, other than start and finish.
It means nothing, other than start and finish.
Thread Starter
Burning Brakes
Joined: Jun 2016
Posts: 1,052
Likes: 101
From: Ohio
excellent - so now higher idle - I found a post (i will have to re-find) about setting the iac, idle and checking the tps - with no sign of codes, no sign of vac leaks - is it safe to mess with the idle screw? i have not touched anything like that wanting to make sure it was not something else first - also - after doing all of this -(cleaning and replacing - ) I ran it on the freeway and side streets - but I did not really punch it - would it help to get out there and let it rip a little? (besides the sheer joy of it all)
thanks again
thanks again
Thread Starter
Burning Brakes
Joined: Jun 2016
Posts: 1,052
Likes: 101
From: Ohio
I found this - (along with a few others with slight variations). is this the correct/best way to set the iac?
There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC). Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC. You will also be playing with the diagnostic connector under the dash. Remove the cover (if it’s still in place). Bend your paper clip into a “u” shape. You will be playing with the two top right hand terminals (“A” to “B”) in the connector.
1. First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It’s located on the driver’s side of the TB. Remove this plug if it’s there.
2. With the IAC connected and the ignition “OFF,” stick the paper clip into the diagnostic connector from “A” to “B.” This grounds the diagnostic lead.
3. Turn the ignition to the “ON” position without starting the engine. Wait 30 seconds.
4. Now, with the ignition still in the “ON” position, disconnect the IAC connector at the IAC.
5. Remove the paper clip from the diagnostic connector.
6. Start the engine and allow it to reach normal operation temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
7. If your car is an automatic, set the parking brake and put the transmission in “DRIVE.” If your car is a manual, leave it in neutral.
8. Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
9. Shut off the engine and reconnect the IAC.
There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC). Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC. You will also be playing with the diagnostic connector under the dash. Remove the cover (if it’s still in place). Bend your paper clip into a “u” shape. You will be playing with the two top right hand terminals (“A” to “B”) in the connector.
1. First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It’s located on the driver’s side of the TB. Remove this plug if it’s there.
2. With the IAC connected and the ignition “OFF,” stick the paper clip into the diagnostic connector from “A” to “B.” This grounds the diagnostic lead.
3. Turn the ignition to the “ON” position without starting the engine. Wait 30 seconds.
4. Now, with the ignition still in the “ON” position, disconnect the IAC connector at the IAC.
5. Remove the paper clip from the diagnostic connector.
6. Start the engine and allow it to reach normal operation temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
7. If your car is an automatic, set the parking brake and put the transmission in “DRIVE.” If your car is a manual, leave it in neutral.
8. Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
9. Shut off the engine and reconnect the IAC.
