Idling too high
Thread Starter
Instructor
Joined: Oct 2002
Posts: 213
Likes: 0
From: Choudrant LA
Idling too high
Ok, I know everyone is sick of hearing about my piece of junk 85, but I've almost got all the kinks worked out. I have done a long list of repair recently to my car, and finally got it running!!!! Here is a breif list of everything repaired and/or replaced:
All gaskets from intake manifold and up
All injectors
Ignition switch
Alternator
Starter
Fuel pump(for those of you who helped me in the previous thread, this was the culprit for my no start problem)
Fuel filter
Now my car has a high idle 1100-1400 and has idled up to 1700-1800. It did idle down once to about 800 rpms, but that's the only time. It runs better than it has since I've had it, but now it has this idle problem. In the previous thread, I asked about a sound in my throttle body, and someone thought it was the IAC. Would this be causing my problem. I also think I have a vacuum leak, which we haven't had the time to find, as a result of all of the other work. For more info see my previous thread below:
http://forums.corvetteforum.com/show...44&forum_id=48
All gaskets from intake manifold and up
All injectors
Ignition switch
Alternator
Starter
Fuel pump(for those of you who helped me in the previous thread, this was the culprit for my no start problem)
Fuel filter
Now my car has a high idle 1100-1400 and has idled up to 1700-1800. It did idle down once to about 800 rpms, but that's the only time. It runs better than it has since I've had it, but now it has this idle problem. In the previous thread, I asked about a sound in my throttle body, and someone thought it was the IAC. Would this be causing my problem. I also think I have a vacuum leak, which we haven't had the time to find, as a result of all of the other work. For more info see my previous thread below:
http://forums.corvetteforum.com/show...44&forum_id=48
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
The vacuum leak is possibly the sole cause of the high idle. The fast idle is caused by unwanted air entering, from somewhere. The IAC controls the idle speed (when it can) at the command of the ECM. If the engine coolant temperature sensor is incorrectly telling the ECM that the engine is colder than it is, the ECM could be commanding a cold, fast idle. Do some trouble shooting... AFTER you fix the known vacuum leak.
RACE ON!!!
RACE ON!!!
Team Owner
Joined: Jan 2003
Posts: 20,320
Likes: 248
From: Summerland B.C. Canada
Instructor
Joined: Aug 2001
Posts: 217
Likes: 0
From: Finland
Just last week buddy of mine was having the same problem in his -86. Cleaned the TB, no vacuum leaks, new IAC etc... We did everything we could but ultimately it did not correct the problem. Finally we tested the TPS sensor with a volt meter and voila! Problem was faulty TPS sensor. Changed to new one and idle is now ROCK solid.
If you have the same just remember to give some time to the computer to adjust to the new sensor.
If you have the same just remember to give some time to the computer to adjust to the new sensor.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Did you disconnect the IAC with the engine running or perform a minimum idle check or adjustment? If so, reset the IAC by pressing the accelerator slightly and starting it. Let it run for 10 seconds; then off for 5. Restart normally and it should be ok.
Thread Starter
Instructor
Joined: Oct 2002
Posts: 213
Likes: 0
From: Choudrant LA
Ok, I've found the vacuum leaks and fixed them. I've also run codes. I got 21,22,33,34,and 42. One thing that I did do was unhook the MAF. It ran rough, but it idled around 800 rpms. Could the MAF be the sole problem causer???
Burning Brakes
Joined: Apr 2005
Posts: 1,110
Likes: 0
From: JUPITER FLORIDA
im having this same problem! same rpms also. i adjusted my tps yesterday and it worked fine, but then i installed an msd and its bad to the high idle. let me know what you guys find out! 
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Thread Starter
Instructor
Joined: Oct 2002
Posts: 213
Likes: 0
From: Choudrant LA
I one of the leaks on one of the air vacuum sensors at the front of the motor. the lines come up from the FPR (I think) and y out to two different sensors. one of the lines was broken off at the base of the sensor. when I held it up to it, it didn't make any difference, so I just super glued it back. No point in replacing the whole sensor for that. also on another line, there was a tiny pin hole. I just put a little silicone on it and it was fixed. Is there a way to test the MAF? Do you know what it's supposed to OHM at? How do you adjust the TPS?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
There is a method to set the IAC and TPS on my site. You need to first set base idle to 450rpm and then set the TPS low & high readings.
The simple TPS test is to slowly advance throttle from idle to WOT while watching the resistance value. If there are any flat spots or jumpy spots it needs to be replaced.
On later L98s the easy MAF test is by direct substitution; the MAF from any late '80s F-body or Y-body can be used. Unfortunately your '85 MAF differs from these later versions so that substitution is not possible unless you can find a known good MAF from an '85 Vette in a bone yard. Here you might try Contemporary Corvette, link on my site.
Don't give up on your '85, you'll get the bugs ironed out and be able to enjoy her once again.
The simple TPS test is to slowly advance throttle from idle to WOT while watching the resistance value. If there are any flat spots or jumpy spots it needs to be replaced.
On later L98s the easy MAF test is by direct substitution; the MAF from any late '80s F-body or Y-body can be used. Unfortunately your '85 MAF differs from these later versions so that substitution is not possible unless you can find a known good MAF from an '85 Vette in a bone yard. Here you might try Contemporary Corvette, link on my site.
Don't give up on your '85, you'll get the bugs ironed out and be able to enjoy her once again.
Drifting
Joined: Nov 2004
Posts: 1,484
Likes: 0
From: Nanaimo, BC
Originally Posted by 65Z01
There is a method to set the IAC and TPS on my site. You need to first set base idle to 450rpm and then set the TPS low & high readings.
The simple TPS test is to slowly advance throttle from idle to WOT while watching the resistance value. If there are any flat spots or jumpy spots it needs to be replaced.
On later L98s the easy MAF test is by direct substitution; the MAF from any late '80s F-body or Y-body can be used. Unfortunately your '85 MAF differs from these later versions so that substitution is not possible unless you can find a known good MAF from an '85 Vette in a bone yard. Here you might try Contemporary Corvette, link on my site.
Don't give up on your '85, you'll get the bugs ironed out and be able to enjoy her once again.
The simple TPS test is to slowly advance throttle from idle to WOT while watching the resistance value. If there are any flat spots or jumpy spots it needs to be replaced.
On later L98s the easy MAF test is by direct substitution; the MAF from any late '80s F-body or Y-body can be used. Unfortunately your '85 MAF differs from these later versions so that substitution is not possible unless you can find a known good MAF from an '85 Vette in a bone yard. Here you might try Contemporary Corvette, link on my site.
Don't give up on your '85, you'll get the bugs ironed out and be able to enjoy her once again.
Check base idle.
Thread Starter
Instructor
Joined: Oct 2002
Posts: 213
Likes: 0
From: Choudrant LA
TPS!!!!!!!!!!!!!!!!!!!!!!!!
It was the TPS. I got a new one, and reset everything it it runs awesome now. I still think that it needs a new IAC, so I bought one, but it was going to take too long to change it out, because I think that you have to take the throttle body off to get it off. Is that correct?? It was too tight of a space to get a wrench in there. Is there a trick?
Thanks for the help!!!!!!!!!!
By the way, I think that it still needs to be changed out, because it still makes a lot of noise that I haven't ever noticed before!!!!!
It was the TPS. I got a new one, and reset everything it it runs awesome now. I still think that it needs a new IAC, so I bought one, but it was going to take too long to change it out, because I think that you have to take the throttle body off to get it off. Is that correct?? It was too tight of a space to get a wrench in there. Is there a trick?
Thanks for the help!!!!!!!!!!
By the way, I think that it still needs to be changed out, because it still makes a lot of noise that I haven't ever noticed before!!!!!
Last edited by eric_daniel; Jun 14, 2005 at 11:59 PM.