I, and my mechanic, are at wit's end with my '90 240 sedan.

Back in April, while in AL, my check engine lite came on. Took it to a nearby "private" mechanic (I never go to the crooks at dealerships). They hooked it up to their computer; then replaced the throttle switch and cleaned the throttle plate.

About 130 miles later, the CE lite came back on. Took it to my mehcanic here in VA. He recommended I take it to the dealership and get the "real deal" computer diagnosis. Fine -- said I needed a fuel pump relay and an O2 sensor.

My mechanic replaced both. Initially, he used a universal O2 sensor to save me a few bucks. When this did not fix the problem, he installed a Bosch O2 sensor. As a "let's give it a shot" attempt, he also replaced the fuel pressure regulator, the computer temp sensor, and repaired the vaccuum line to cannister. No dice.

I took it back to the dealership, and got another diganosis. They found 3 codes --- 213 (TP switch), 113 (short term O2 sensor, and 282 (long term O2 sensor). Great --- a 5-day old Bosch O2 sensor is deemed to be inoperable.

At wit's end, I took it to a "private" Volvo/European car expert. They've pulled their hair out trying to diagnose it. Last week, they thought they'd done the trick. But I drove 15 miles back to my house, and the next day, the CE lite came back on.

The car loads up at idle. Burning richer than Donald Trump. Once out on the highway, she runs like a champ, but at a red light she shakes and shimmers from burning rich. My mechanic has checked all the mechanical parts....they are all in perfect working order. He thinks it must be an electrical problem (short, grounding, corrosion, etc.) He's worked on literally thousands of Volvos and has never had this sort of problem.

Any other ideas ???

Thanks for any help.