I have an 88 240 that is running really rough at idle, but runs fairly well at high rpms (above 2,000). I thought that I had a bad AMM, so I purchased a used one on ebay, but swapping the two did not product a difference. The only other thing that I can think of that would cause these symptoms is a vacuum leak and since I am unable to find one I am still trying to diagnose the AMM.

If I unplug the AMM the car runs the exact same as it does with it plugged in, if the AMM was good I would think that unplugging it would cause the car to run worse, what do you think?

I followed the testing procedures in the Haynes manual that I have. It says that the resistance between terminals two and three should be 3.5 to 4 ohms. Mine shows no resistance, my voltmeter reads 0.00. I do not have much experience testing electrical parts, am I right to be using the 20K setting on the voltmeter for this type of part? I am reluctant to purchase a new AMM just based on this one test especially when I may have already wasted some money on a used one. Does anyone know of any other testing procedures for the 007 AMM?

Greg