Hello.

My car is having a really odd idle issue that is happening with complete unpredictability.
Car is a 92 jdm FD. Running Haltech Elite.
Car typically idles around 1200-1300 after warmed up.

Sometimes, the car starts up fine and drives with no issue.
Other times, it starts up fine, and then anywhere between 5 minutes (no driving) to 20 minutes (mid drive) later, my idle will start to increase and hold at the new number.
Sometimes will only increase to 1500. More often will go up to 2000+. Sometimes 2500. One time as high as 3000.
There is no consistency as to when it happens, if it all. Not a certain air or coolant temp, not a consistent amount of time after starting the car, nothing. Sometimes, I'll be at a dead stop at a stoplight when it starts. Sometimes it'll start as I'm cruising. I'll hear it start, as it sounds like im blipping the gas pedal a few times, and then it'll go up as if I'm holding the gas pedal down steady. There is no dead area in the pedal once it starts. My foot can be completely off the pedal, and I'll hear it rev up a few times, and then hold steady at the increased idle. But if I do blip the gas pedal, or press in on it at all, it is as if I'm using the pedal normally... just with a new baseline idle.
It is not a constant hunt, but a surge and hold. When it is first starting to do it, it may surge 2-3 times before it decides it is going to hold at the increased number. Usually skips the hunt and goes straight for the higher idle though.
Sometimes, I can turn the car off for 5 minutes, and upon restarting, it is back to regular. Sometimes I restart to find it goes back to the newly increased idle point.

Took off the ISC and sprayed it with carb cleaner. Jumped it a few times to try to make sure it was clean. If there is anything else I need to do with that to clean it more thoroughly, please let me know. The Dale clean out thread that everyone references seems to be a dead link nowadays.
Have checked for vacuum leaks by spraying down accessible hoses and caps with throttle body cleaner. Did not find any issues there. Are there areas that are more common to leak that would cause this issue that I should look a bit more in depth on?
Checked the throttle cable and didn't notice anything wrong.

Planning on trying the TPS adjustment this Sunday.

Figured I'd start a thread and ask for any other suggestions to try/look for in the event that the TPS adjustment doesn't take care of the issue. Time to work on the car is limited, so want to go into Sunday with a few back up ideas in case TPS doesn't do it.
Weird part is that it is not consistent. I drive roughly 6 miles to work, and 6 miles home. Sometimes it drives fine going to work, but starts up as I'm going home, or vice versa. Sometimes there's not an issue on either drive. No real change in ambient temperature between the times I drive.

I do have a slight electrical drain that I believe is unrelated, but figured I'd mention it just in case. 91 octane gas and I do premix.

Thanks for any help/suggestions!

 

Read my recent idle troubleshooting thread. Things are a bit different with the Haltech but it all comes down to the same thing - more air is getting into the engine than should be.

Dale

 

I did read that thread, as you posted it a few hours after I made this one.
Definitely appreciate the knowledge.

My high idle issue is just so inconsisent, which is what prompted me to ask about my specific issue.
I understand that high idle means air is getting in somewhere.
I'm now thinking I have a gasket somewhere that is somehow sealing, and then unsealing, and then sealing, and then unsealing as often as it chooses to.
I realized the issue happens more often on my drive home, after the car has been sitting in the heat/sun for 8 hours, whereas the car is sitting in cooler temps in the garage before my drive to work. Perhaps sitting in the heat for so long before the drive home causes the gasket to expand and lose it's seal.

update: starter fluid sprayed at the lower intake manifold caused a change this time. Idle went down for a sec, before going back up. I know starter fluid would USUALLY make the idle go up instead of down, but that's not always the case.
Ordering a new metal gasket now.

I'm going to do a search, of course, but anything I should be aware of when getting down there to get the new gasket in? Anything I'm taking apart that will also need a new gasket, or anything else I should look to replace since I'm getting down there anyway? First time removing the LIM. Thanks!