2002 C70 Weird computer reset issue, poor running intermittent

[Sommerfeldt]

Have you done a compression check on it?
I don't like to be the one to bring it up, but do you have any way to clone a new ECU, and see what that does? Might not be very cost effective to do, but you seem to be exhausting most other paths.

- S

[misha]

I would check ECT connector for corrosion...for both sensor and wiring loom side...since it's happening ONLY in cold weather...and they don't always set a code especially since it's intermittent fault.

One more thing...Maf connector is also a problem on these cars....solution is to zip-tie it down or to clear the gap between pins as far as possible with a little flat precision screwdriver.
I needed to do that about a year ago and had similiar symptoms.
Re-seating the connector a few times did help but as soon as i leave it overnight problem re-appears....untill i realised that connector is the problem.
Visual inspection didn't revealed nothing wrong with it.
No problem since.

[dobrosailor]

Do these cars run open loop when cold like my 1999 Jeep GC? This would rule out any O2 sensor issues. So I found that the wires across the head were shorting under the covers. I particular, the two going to the solenoid (?) on the rear cam on the belt side of the motor were shorted out. I Fixed all the shorts and bad wiring I could find. No real noticeable difference, when the car is cold first thing in the morning it starts quickly then appears to try to flood out. This is when I Raise the idle to 2-4k and it clears out driving fine the rest of the day. I know this is bad for the cylinders to start their day with the oil rinsed off by excess fuel.

Compression is good to answer one question. I worked all the connectors in case there was a bad connection. THe car runs beautiful gets 24.5 MPG city and country driving. It does still drop a cylinder or something wide open throttle, it pulls but not as hard as it should and then when I back off the throttle to about half way, it pulls like crazy as if the 5th cylinder kicked in. Has the original ETC module and I have cleaned it recently.