High Idle, please help!

[guillebeau5150]

My 86 is driving me crazy with this problem, its just random not necessarily a specific factor like heat or milage, but it will just idle at 1500 rpms sometimes. I'd say it happens about 50% of the time. It does not do it from startup however, and if it is in hight idle I can shut car off and crank back up and it will idle normal (900 rpm seems to be the normal for this car is that correct?). But give it a few minutes and it will usually rev lightly then work its way up to 1500 again. So far I have tried the suggestions I have found on this site, set tps low as it will go .88 I think, cleaned idle air bypass, and just yesterday replaced ect which on the first test drive seemed to fix it then a second test drive it was idling 1500 before I could get on the highway. Please help me with this, it is about to drive me insane!

[dpmeeks]

replace your IAC

[guillebeau5150]

If it was the IAC causing the problems when it's idling high shouldnt I be able to disconnect it and the idle drop? when I disconnect it now nothing happens.

[dpmeeks]

if its stuck then disconnecting wont make a difference..

could be a vac leak also.

[BrianO]

is the line to your FPR intact?... reason I ask is when I replaced my ECT I barely touched the FPR line and it cracked it..

[guillebeau5150]

Forget what I said about disconnecting the IAC, when its disconnected (while running and at high idle) the idle stumbles for a few seconds then shuts off. I have tested the IAC and ohms checked out and it is getting ground. I checked it during engine running checking the voltage that the computer was sending to it and was getting around 8.2-8.3 volts during proper idle but when it kicked up to a high idle it dropped to about 7 volts. Im not sure how the amount of volts related to the IAC action but it seems the lower the voltage the more it opens up, is this how it works? If so then it seems the computer was telling it to open up more for no reason.

Also checked for vacuum leaks but didnt find any, plus if it was a vacuum leak wouldnt the idle be consistently high?

[GAboySVO]

Search for TPS. Its causing your issues. You will need the base idle sticky write up to install the new TPS and get everything working correctly.

[turbosvo]

I had the same problem a few days ago, mine was idling high. finally moved the idle screw down and reset tps and a new gasket on the iac an good as new

[guillebeau5150]

Ive about had it. I set base idle, got it at 750, then got the tps to .90. Disconnected battery for about an hour and have driven it and stopped and started it a few times and now after driving just enough to get into 5th gear it idles at 2000 nonstop. It will only go down if its cut off for a few minutes then cranked back up. I checked the IAC while its idling at 2000 and it reads 5 volts, when it first cranks at about 1200 (if Im lucky) its at about 2.8 volts. Whats going on? It seems to me that the computer is sending the higher voltage to the IAC but why? Could it be a faultly computer? Please help, this is driving me crazy.

[fstbk65]

I have a similar problem. It starts fine but after driving will maintain about 2000 rpm's just sometimes. I can stomp the throttle and get it to go back down sometimes. My throttle body linkage seems worn some and I can manually push the butterfly closed at the linkage and it slows back down. It doesn't move much but it makes a difference. I haven't checked any sensors or switches yet. Been fighting another gremlin lately. This one is next!

[86XR4Ti5SPD]

Was experiencing identical issues with mine a month ago after several tps resets. Would start/idle fine, but once warmed up and at stoplight, up in the 1,500-1,700 range intermittently. Usually a shut down and restart brought it back to 950-1,000. Reset the tps to spec yet again, but this time was careful not to snug down the screws too tight. This appears to have been the source of my high-idle problems...perhaps some binding created by the heating/expanding of the tps when tightened down too hard. Hope that's helpful.

[guillebeau5150]

I checked the tps after tightening it up and it read a .902 so that should be okay right? Also have checked for throttle sticking and everything with that checked out okay. Im pretty positive its the IAC opening up way to much. But the IAC works fine and all checked out with it, its the computer sending it too high of voltage. I dont know if its something else not related with tps or iac making the computer send a high voltage or if the computer itself is faulty. Where do I go from here? It is now at a constant 2000 rpm idle.

[BrianO]

you need to check your TPS with an analog guage..make sure there are no dead spots in it.. it may show it's set perfectly, but could be a bad spot on the pot inside.

if/when you unplug the IAC the car should die...unless it is at operating temperature, then it will idle.

[blueboss]

But the IAC works fine and all checked out with it, its the computer sending it too high of voltage. I dont know if its something else not related with tps or iac making the computer send a high voltage or if the computer itself is faulty. Where do I go from here? It is now at a constant 2000 rpm idle.

What, if any, codes is the EEC displaying? You have read the computer for codes right?

[GAboySVO]

Did you replace the TPS yet? It is your problem. The TPS is a reostat and it has a dead spot. When the the throttle is opened to above 2000 RPM and hits the dead spot, the computer resets this voltage as it base reference voltage and thus the issue you describe.