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At idle, car oscillates rpm's. Check Engine light is on. Started intermittantly but has been getting worse and happens 100% of the time now. I see two upstream sensors and one downstream sensor exists. 2001 SLS. 85,000 miles on car.
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Did they check to see if any reprogramming or up dated software for the PCM is avilable ? Sometime computer gliches will cause problems an the dealer can do a reflash to fix the problem . Did they look at TSB - technical service bulletin .You could go to the GM TDS web site an enter your vehicle ID # or VIN an it will tell you if any updated software is available . Also could have a lose or corroded connection ,body grounds etc.... How to Program and Reprogram OBD 2 Modules Example Code P0326 Knock Sensor
intermitten problems are the worse, when it wont start check fuel pressure with a gauge, and then check for spark, i have spent days on problems such as this, what you have to find is what is missing, fuel ,spark, is maybe coolant leaking into one or more cyls, i have seen air in the fuel system that only cause problems when under hood temp is high, open the hood and it cools enough to to start, hope this helps
You should verify you have proper fuel pressure. Check with a gauge when cold and hot. Possible clogged fuel filter is not allowing enough gas to feed engine. Verify pressure at idle and also under load when driving.
Sounds more like the Throttle Position Sensor or another sensor is letting the engine RPM's drop too low. When the RPM's are too low, the oil pump is not pumping enough oil.
These cars are notorious for intake manifold leaks. This could also be a throttle position sensor. If you have a MIL (check engine light) I would scan it with an OBD II scanner and pull the relevent code off the scanner it will give us a much more accurate direction to proceed
I took mine in to change the plugs and they said there are four O2 sensors in the fuel mixture system and two were bad. I didn't replace them since they were a little pricey ($500 to replace both) and I have 103,000 on the car. Has very similar roughness and occasional oscillations, but no stalling. Hope this helps.
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