I’m having a weird idle issue with my ‘91 Integra, and I’m running out of ideas. When I start the car cold, it idles fine, but after a few minutes; the RPMs start fluctuating between 1,000 & 1,800 in a steady rhythm.
It’s like a wave, up & down, and it doesn’t stop even after the engine warms up.
I’ve already cleaned the IACV and FITV, checked for obvious vacuum leaks, and made sure the throttle body gasket is intact.
But the issue persists. Could this be a cracked intake manifold gasket / a hidden vacuum leak under the intake manifold? I also heard something about the thermostat affecting idle, but I’m not sure how that would cause surging. Checked Roaming idle - Stock Engine-Bay ComponentsGenerative AI guide for reference .
Has anyone dealt with this before? Any suggestions on how to track down the problem without tearing everything apart? Any help would be appreciated!
Are you driving an auto or manual? I was having this issue with my 91 automatic after my EGR valve (only on automatics) wasn’t holding a vacuum. It seems to happen whenever air isn’t flowing properly into the engine, be it vacuum leaks, gunked up throttle bodies, etc. If you’re driving an auto, this probably happens when you put it in park right? One thing to also check is your throttle cable. If it’s too tight such that the leaf is a bit open, that can also throw off the idle speed and so the computer will basically be “searching” for the right idle speed. I think some forum posts often refer to this issue also as “hunting idle” or “roaming idle.”
Here’s some other links and videos from my own research on the issue back when I was fixing it:
Checked Roaming idle - Stock Engine-Bay Components Generative AI guide for reference .
