The information in these forums has been helpful, but I am still experiencing a problem which I have been trying to solve for some time. My 1995 Volvo 960 has an "unstable" idle, and is giving error codes. The car has about 120,000 miles. The engine code that has come up for the last couple of months is 2-3-2. I have replaced the spark plugs, oxygen sensor, flame trap, and throttle gasket. Did not solve the problem, but replacements were probably needed anyway. In the last few days, had the fuel injectors cleaned - not pressure cleaned, but soaked. Now in the last few days have gotten a transmission code 2-1-3, and today got a engine code of 4-1-1 along with the 2-3-2. I read that the transmission code is "Throttle position signal too high". I had previously removed and cleaned the sensor - perhaps it is bad. Don't know what a engine code of 4-1-1 is. When the car idles it acts like a cylinder is missing. While the engine is running, I have pulled the spark plug wires one at a time. No change to the engine when I pull the first wire, but with each of the others the engine slows a bit and the idel gets a little rougher. I have tried the same thing with the fuel injector wires and it behaves the same way as with the spark plug wires. No change on number 1, but a change with each of the others. I connected a voltmeter to the spark plug wires and the fuel injector wires and in each case the voltage fluctuates as the engine is running (as I think it should).

Could a bad throttle position switch/sensor cause these symptoms?

Any help/advice on this is appreciated.