[T3] cool weather idle hunt

Daniel Nohejl d.nohejl at gmail.com
Tue Jan 17 16:12:17 PST 2017

O, boy, what a mess!

Car started fine this morning but idled very roughly when cold. I made a note to myself to adjust idle and timing after work in case changing the AAR adjustment threw off the idle speed. I figured that was possible depending on where the AAR was set when I last did the idle. 

After getting off the highway on the way to work, the motor stalled every time I took my foot off the gas but for one time when the idle stayed steady. After work, it took five tries to start the car. Very unusual as it always starts on the first or second try. I pulled out of the parking lot and stalled. I then proceeded to stall every single time I let my foot off the gas but it drove perfectly well on the highway. I got close to home and stalled at a light. This time it wouldn’t start. It caught on one or two occasions but wouldn’t fully fire up. Then, it’d crank and crank but nothing else. Of course it started pouring rain after a few minutes…..

Anyway, I checked the following partly by myself and partly once Jessica showed up (the benefit of breaking down only 2 miles from home)…the list isn’t in sequence:

—fuel pump relay clicked and pump primed when key was turned
—FI power relay clicked when key was turned
—MPS sensor plug wasn’t loose
—all injector plugs were secure
—trigger points connector was secure
—injector grounds and ECU ground at case center line all secure
—wires to generator were secure
—12V to black/white wires from FI ground to T2 connector and 12V from T2 connector to ECU
—resistance of both temp sensors was fine
—dwell was ok and everything in the distributor looked fine
—12V to coil
—took out the ECU and verified that the plug wasn’t loose

It was pouring out and I was staring at the ECU laying there in the cargo area and decided to take the plunge b/c Jessica showed up with one of our spare ECU’s. I plugged it in and the motor fired right up. Just to confirm I wasn’t hallucinating, I tried the ECU I had just removed. No start. Tried pressing on the harness in case it was loose on the card edge. No start. Put in the spare ECU and it fired right up again and I drove home without any problems!!

So all along my "intermittent warm idle lope" was the ECU taking a dump until it finally died?!?! Is that even a thing??

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