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Old 10-11-2002, 09:44 AM
Ron Brooks Ron Brooks is offline
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Join Date: Jul 2002
Location: Stony Brook, NY
Posts: 160
"Cold" idle problems after new O2 sensor

My first running problem on my 88 300SE. I brought the car in for its NY State inspection to my usual shop. The car has run fine since I bought it, approx 2,000 miles ago. It has 78,000 on it now. Passed safety fine but failed emissions due to bad O2 sensor. The shop installed the new one and upon picking it up, the mechanic said everything's OK, just see when you start it in the morning if it runs OK because it's running in the acceptable range but in the lean end of the range. He said this while having a "Fluke" hooked to the car. He said the car needs to be adjusted when cold and also when warm.

The car ran pretty crappy the next morning on start-up. It started fine, but after running for 30 seconds or so, when shifted into gear, it shudders and rpms drop to about 500. It has stalled once. Once it warms a bit it runs fine. Figuring it had to be re-adjusted, I decided to change the plugs. I bought copper core Bosch plugs. Brought it back to the shop, they re-adjusted and it is STILL the same. They claim they did nothing wrong.

None of this happened before the sensor was changed. It ran fine warm or cold. Any ideas what could be the problem? Again, it only runs poorly until warmed.
Ron Brooks
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