Surging Idle After Bleeding Coolant System and Engine Rinse

[Cloudbase]

Just like the title says. I replaced my 76C thermostat with an 80C one. Afterwards I bleed the coolant system multiple times. There was coolant everywhere so I lightly rinsed my engine off. I know, I know, bad idea for brittle 80's connectors.

The car ran fine that night and for most of the next day. Then the following afternoon it took a while to start, but ran fine. That night I starte it up and immediately got a CEL, followed by a surging idle. The idle will surge from 700 up to 2000 rpm. In the last year I have a new ICV, TPS, All new vacuum lines, coolant ECU temp sensor, and good AFM and intake boot. Where would you start. I'm thinking ICV or vacuum leak. I'm away from home until tomorrow so I can't do the stomp code test. Just looking to get a head start.

Thanks.

[jlevie]

I'd start with a smoke test and a check of the TPS.

[Cloudbase]

What would make you suspect TPS over ICV. Think it's filled with water or coolant from the bleeding and engine rinse?

[jlevie]

It could be either, but water getting into the TPS (or a bad TPS) will prevent the DME from knowing that the throttle is closed. But I'll bet on intake leaks being at least part of the problem.

[Cloudbase]

^ Was thinking water would be part of it. TPS was replaced less than a year ago w/ new one, so if it is bad it's because I killed it.

Did the stomp test today. It threw code 1262

"1262 Idle Speed Actuator There is a break or short circuit in the wiring to the idle actuator or the wire from the DME is defective or the output stage in the of the DME is damaged. This code will also be stored if the engine stalls at over 600 rpm."

Is the Idle Speed Actuator the same as the ICV on the M20?


After the test the CEL extinguished and it purred like a kitten. I figured the symptoms would re-present when it warmed up and switched to closed loop mode. I set out on a prolonged test drive, but got nothing. I'm wondering if there was residual coolant / water somewhere causing a short. Or if it is something more persistent that will rear it's ugly head again.

It could be a vacuum leak, but I really doubt it. I replaced all of my vacuum hoses, intake boot, along with all related electronics last year. My bet is that it is indeed electrical since it presented right after I bleed the coolant system and rinsed the engine.

[paperplane94]

I bet there was a short in the ICV connector.

OCD like me? pull the connector boot off and have a look.

[Cloudbase]

I pulled all of the connectors and blew them out with compressed air. But nonetheless sounds very plausible.