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Maybe having someone not familiar with the system prove how much they do not know, might throw a few more options into the mix. The following is such an attempt.
Having read all the replies to this thread, I get a sense that the system is running lean via the high idle. 1000rpm at idle is too much. Old school carb basics, Lean increases RPM, Rich decreases. Found it to be true even with injection systems with a greater sensitivity to slight out of spec ratios over all operating RPMs.
Any other codes? Sometimes other codes help point to the actual cause. I never read previous posts under a different heading if there were any.
One process I believe should always start a dianostic regime where one attempt at repair does not eliminate the code. Remove, clean and replace the ECU grounds on the intake manifold, along with any negative battery to block and block to body connections.
Do the same with positive battery connections while the negative is disconnected. Verify that the battery is capable of delivering full voltage.
Clear codes and if they reappear, continue searching.
From this point on, all is just rambling of the mind, attempting to define a single or multiple fault that contributes to the code that might coincide with work under the auto.
Oil change causes a code. Get under the car and look at what would be necessary to change the oil and filter. What wires, hoses, etc could be touched, moved bumped etc. Do not assume the mechanic stayed close. To get leverage to remove filter, where would his elbow be and where would the filter wrench end up after release. Even look from above. Two wires/hoses come off and when replaced are exchanged?
Lean from air leak. Obvious places checked. What about the not obvious.
Charcoal Vapor cannister somewhere underneath and its hoses. Flame trap system/(Pos Crankcase Vent) system hose/box etc out of position or damaged. Hose ends cracked/loose on connectors. If dealer during oil change checked, maybe they didn't get it quite back together?
Lean from low fuel pressure. Coincidental to oil change. Any history of the 960 fuel lines inside tank failing like the 240s? Prepump if any not working? Do the 900 pumps have a single power feed from the relay or two? Fuel check valve stuck partialy closed creating lean mix? Pressure is there but system not delivering volume. Clogged filter? FPR out of spec or inline check valve if any faulty?
Is the AC system on? I've heard (and never verified) that at some point auto makers cycled the AC even during the winter to help with defrost. So if your AC was getting a signal to run and was low on charge to not pull down the engine, the mix would be lean.
OK, ramblings over. I hope one of the above clears the code.
Duane
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