My car is an 88 240 with M47 tranny, 007 AMM, and stock everything under the hood. I finally got my car to stay running by switching out the 511 ECU with a 554 one from an 88 parts car. Along the way, I had replaced the AMM with a new one, new oxygen sensor, swapped TPS with another used one, and checked the IAC motor for sticking motor. The IAC was fine, and adjustments to the TPS have not been successful in lowering the rpm. Should I suspect the TPS of being faulty and replace it ($78)? Is the different 554 ECU to blame? (A guy at the parts counter in the local Volvo dealership said the 554 should be an o.k. replacement for the 511). Or are there other possibilities that I am missing? I really want to get the idle back down to where it belongs soon, as I have experienced some difficulties shifting back into first or reverse when the engine is racing ( I hate the sound of grinding gears!). Thanks in advance for your suggestions.