Hi Brick people,

I've got a 1990 240 sedan with an intermittent problem. At cold start the engine immediately fires up but feels like it is running on 2 cylinders. The whole car is shaking. I apply gas and it continues to stumble and jerk but after about 30 seconds, it smoothes out and runs perfectly as if it's throat just needed clearing. If I turn it off and restart, it starts perfectly and runs like a champ.

I ran the car through all 3 diagnostic levels using test socket #2. It had a check engine code of 3-3-1 (bad throttle pos switch) and I cleared the code, and swapped in a good TPS just to be sure. I then ran diagnostic proc #2 and all systems checked out without faults. I then ran diag proc #3 and all 4 injectors and the IAC were activated as they should be.

I cleaned the MAF and checked the hoses for vacuum leaks but didn't see any.

I pulled the hose off the FPR and looked for gas but it seemed fine.

I disconnected all of the injectors and all of the wiring harness connectors and reconnected.

Restarted the car when cold and the problem seemed to be gone. No rough idle at start up.

I parked the car overnight and tried starting again and problem seemed to be cured.

Last night I tried one more time and it was back. Started great but really horrible rough idle for 30 seconds then fine after that.

Checked plugs, cap, rotor and wires and all seemed quite new.

Fuel filter has not been changed but if it were bad, I'd think there would be worse symptoms in drivability and such but car runs wonderfully after 30 seconds.

My question is would a lean mixture or rich mixture or both cause these symptoms? Could the cold start valve be inoperable? Could the Coolant temp sensor be defective and if so wouldn't that cause problems until the car truly warms up. This problem disappears after 30 seconds, certainly not enough time for the car to warm up.

Any thoughts?

I promise I have looked in FAQ's and done a search on all of this but have not found any definitive help.



Thanks, Tony