1986 Reliant K-Car up and down revs

I would gather that you have tried to dump diagnostic codes and didn't get any?

I had an O2 sensor go bad on my 88 Reliant. Gave the same symptoms.

It's probably the AIS (automatic idle speed) motor. It could also be a cooked wiring harness, which is what happened with our old '88 Omni. It would too fast -- sometimes as fast as 2,400 rpm. The key was that it was more likely to do it it wet weather. The fix was to open up the wiring harness and re-insulate the wires within. The mechanic who did this said that he'd seen this a few times before, especially with Omni. His theory was that the tight engine compartment on 2.2L Omnis did not allow enough cool air to travel over the engine, and the insulation in the wiring would be damaged by heat. We'd gone through two AIS motors before we got it fixed for real. It never did generate any codes.

I'm assuming that you have either the 2.2L or the 2.5L.

-- Jeff Wieland

Hi, Carl. Thanks for your reply. The diagnostic codes didn't indicate any problems. I'll look into your suggestion.

Hi Jeff. Thanks for your kind input. It is a 2.2L engine. I'll have your ideas checked out.

Can you be more specific on which wiring harness needs to be checked in this situation, I have a 2.2 turbo '85 that has also been doing this, random (but starts to want to do it after warms up) revving and lowering of idle. Can rev way too high. All vac hoses repaired/checked (which fixed a problem with the wastegate not kicking in), removed and cleaned the whole throttle body etc. No codes when it does this. Definitely the idle motor is activating the overrevving cuz if I disconnect it the overrevving goes away (but I can't run the car like that of course or it won't rev high enough for cold running.) Is it only the wires for the idle motor itself that are in question here on the insulation, or ANY wires running around under there? thanks!....Frenchy

Frenchy, the harness he is referring to is not the same on your vehicle. On Haywards vehicle the harness would rest on the intake/exhaust manifold and short out causing the AIS motor to go crazy, all he has to do is check for damage to the harness and get it off the manifold, You could have a problem with the TPS sensor, coolant temp sensor, map sensor or AIS motor. If it were mine I would have the system scanned to see the values of the sensors. A sensor can be out of calibration without setting a fault code

Glenn Beasley Chrysler Tech

Thanks very much Frenchy and Glenn for your help. It was the TPS sensor and after replacement it seems to run okay now.

Michael.