High IDLE cause?
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
Remove the base idle plug.
Connect a paper clip, to your diagnostic terminal under your dash connect to terminal A and B (the top right two pins).
Turn on ignition but don't run the engine.
wait at least 30 seconds and then remove the idle air valve connector (IAC) (the square plug) then turn off ignition and unplug the paperclip.
Now remove the timing connector a single wire near the fuel pump relay.
Start your vette and set the idle speed to 400 rpm in neutral (auto trans) 450 rpm (manual trans) then check your throttle position sensor,
the top two wires it should be set to 0.54volts dc, also confirm with engine off that the tps rises to 4.5 volts at full throttle.
Turn off the ignition and reconnect the iac valve connector and timing connecter and start your vette.
it should go to 1200 rpm then drop slowly to 600 rpm, take the car for a 15 minute drive with the usual stop lights.
It is normal for a little hunting while the ecm relearns, also do a few spirited take offs.
All should settle after 15 to 30 mins normal driving and have a stable idle.
BTW spraying anything on the outside of the IAC does nothing other than clean the outside of the IAC.
Connect a paper clip, to your diagnostic terminal under your dash connect to terminal A and B (the top right two pins).
Turn on ignition but don't run the engine.
wait at least 30 seconds and then remove the idle air valve connector (IAC) (the square plug) then turn off ignition and unplug the paperclip.
Now remove the timing connector a single wire near the fuel pump relay.
Start your vette and set the idle speed to 400 rpm in neutral (auto trans) 450 rpm (manual trans) then check your throttle position sensor,
the top two wires it should be set to 0.54volts dc, also confirm with engine off that the tps rises to 4.5 volts at full throttle.
Turn off the ignition and reconnect the iac valve connector and timing connecter and start your vette.
it should go to 1200 rpm then drop slowly to 600 rpm, take the car for a 15 minute drive with the usual stop lights.
It is normal for a little hunting while the ecm relearns, also do a few spirited take offs.
All should settle after 15 to 30 mins normal driving and have a stable idle.
BTW spraying anything on the outside of the IAC does nothing other than clean the outside of the IAC.
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
Stock 90 TPS is non adjustable however it can be made to be adjustable with a small round file or install an earlier adjustable unit.
You now have a tuning aid.
Playsdixie:
Posted procedure is from this forum & is in fact for a MAF system however it will work on a speed density system. It has been a number of years & I do not recall if the spark control was disconnected or not.
Maybe try it both ways??
Thread Starter
Instructor
Joined: Apr 2014
Posts: 230
Likes: 7
From: NJ
Yesterday when I got home, I was able to do this process, Problem I have now is when I started the car up this morning it did not want to idle and kept dying on me I had to hold the brake with one foot then give it a little gas then shifted to drive. Once warmed up it was better, still not idling @ 450-500 I would say its at 900-1100. So I got to work this morning and I had a bottle of carb/choke cleaner. I sprayed the TB until bottle was empty! Restarted car and it was able to hold idle, only I think its because it was already warmed up, will try to start it up in a little while see what happens?
Now I have seen it said to clean the pinicle? of the IAC, is this located in the TB? If so is it under that piece in the middle of the TB?
Can I adjust the min idle screw with out going thru the whole process? If I was just to open it up a little wouldn't that let more air in to help it maintain Idle? I am thinking I may have closed it too much? is that possible??
AGAIN GREAT THANKS ALL THIS IS VERY HELPFULL!!!
Now I have seen it said to clean the pinicle? of the IAC, is this located in the TB? If so is it under that piece in the middle of the TB?
Can I adjust the min idle screw with out going thru the whole process? If I was just to open it up a little wouldn't that let more air in to help it maintain Idle? I am thinking I may have closed it too much? is that possible??
AGAIN GREAT THANKS ALL THIS IS VERY HELPFULL!!!
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
you cannot turn that screw without going through the procedure....when done, your car should idle at 650 in drive....the pintle is the cone shaped end of the IAC....if you have a carbon problem, then remove it, clean it...replace it if it's old...and clean out the orifice where it screws back in....you really need to do the min idle, set the tps, and retime it...it's the only way....you just can't turn one screw...if you already have, it may explain your issues now......using the forum threads, shouldn't take you an hour to finish.....still not sure if you should disconnect the distrubutor wire when setting the idle....good luck.....Paul..
Thread Starter
Instructor
Joined: Apr 2014
Posts: 230
Likes: 7
From: NJ
Thanks for your reply.
So yesterday I was able to run thru the whole procedure again, and it appears that when I did this the day before since I was in a rush, I connected the IAC wrong, its a square plug and I plugged it in wrong, so I was able to correct that, what was odd was the check engine light never cam on? Also the Idle once warmed up was better, problem was when starting cold it would die immediately. So I plugged the IAC plug in correctly and then ran thru the whold procedure again, much better now, Idle still has to come down some though. Question, when I unplug the IAC then re-start the car it is difficult to keep running, more difficult to maintain a steady idle like this. Could this be another problem? If not what is a good way to set idle with IAC unplugged. Usually when I would get some what of an idle then get out of the car to adjust the min idle screw the motor would die. I do know once I have my idle set I will have to re-time the motor. Should I set timing to 6*, 8* or 10*. I only run premium in the Vette.
Thanks again everyone!
So yesterday I was able to run thru the whole procedure again, and it appears that when I did this the day before since I was in a rush, I connected the IAC wrong, its a square plug and I plugged it in wrong, so I was able to correct that, what was odd was the check engine light never cam on? Also the Idle once warmed up was better, problem was when starting cold it would die immediately. So I plugged the IAC plug in correctly and then ran thru the whold procedure again, much better now, Idle still has to come down some though. Question, when I unplug the IAC then re-start the car it is difficult to keep running, more difficult to maintain a steady idle like this. Could this be another problem? If not what is a good way to set idle with IAC unplugged. Usually when I would get some what of an idle then get out of the car to adjust the min idle screw the motor would die. I do know once I have my idle set I will have to re-time the motor. Should I set timing to 6*, 8* or 10*. I only run premium in the Vette.
Thanks again everyone!
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
If the engine is not running smoothly, if there is any kind of misfire that problem needs to be corrected before setting base idle.
If it does run smoothly but dies before you can get to the adjustment:
Before starting the engine turn the base idle screw in a full turn or 2 whatever is required to keep it running with the IAC disconnected. Set the base idle. If the engine will not idle @ 450 rpm you have other issues.
If it does run smoothly but dies before you can get to the adjustment:
Before starting the engine turn the base idle screw in a full turn or 2 whatever is required to keep it running with the IAC disconnected. Set the base idle. If the engine will not idle @ 450 rpm you have other issues.
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Thread Starter
Instructor
Joined: Apr 2014
Posts: 230
Likes: 7
From: NJ
timing set to 6* and I am trying this after I have driven car for about 10 miles coming home from work. I have a Tach to hook up under hood, but where is the - neg coil wire on this car? I do not trust the tach on dash.
Thread Starter
Instructor
Joined: Apr 2014
Posts: 230
Likes: 7
From: NJ
Was able to keep motor running by turning min idle screw in a few turns, but once I come close to 500 rpm motor seems to stumble and tries idle begins to search so it will not maintain a steady idle to confirm where I am at. Eventually if I do not give it gas motor will stall unless I turn min idle screw up a little. Like I mentioned previously timing set at 6*.
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Was able to keep motor running by turning min idle screw in a few turns, but once I come close to 500 rpm motor seems to stumble and tries idle begins to search so it will not maintain a steady idle to confirm where I am at. Eventually if I do not give it gas motor will stall unless I turn min idle screw up a little. Like I mentioned previously timing set at 6*.
Thread Starter
Instructor
Joined: Apr 2014
Posts: 230
Likes: 7
From: NJ
yes, engine has reached temp, I hear the cooling fans come on and off. It is after about a 15-20 min ride home, and yes the iac is unplugged after waiting 30 secs + with the ignition on motor not running.
Thread Starter
Instructor
Joined: Apr 2014
Posts: 230
Likes: 7
From: NJ
No the motor is not misfiring, I went thru the whole procedure several times, this last time I tried closing the min idle set screw just like 1/2 a turn, it stalled but I left it at that to see what happens when I plug everything back up. SO, after plugging all back up, like the IAC and the timing plug the car would not hold any idle, it would stall, so I reversed and went thru the procedure again, this time opening the min idle set screw 1/2 turn and it brought me back to where I was previously. I am thinking I need to clean or replace the IAC? Curious to hear anyone's thought on this?
Most important thanks all for your help!!!
Most important thanks all for your help!!!
Thread Starter
Instructor
Joined: Apr 2014
Posts: 230
Likes: 7
From: NJ
forgot to mention, idle not at 450! its more like 1200! 900-1000 in drive. I think since with the TB blade closed that much the motor is choking and that's where the IAC should be letting additional air in? But since its not that's what makes me think the IAC is dirty or bad. I have not cleaned it, am having trouble finding a wrench or socket to remove it?!
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