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Been struggling with a very rough idle/hesitation and surging on acceleration (hot or cold) problem for a few years. My beloved '87 240DL wagon runs fine all summer, and when the wet and colder weather hits here in the Pacific Northwest, it starts running rough. Put in a rebuilt AMM 3 years ago, and new airbox shutter thermostat at the same time. Over time, have cleaned throttle body, put in new O2 sensor, and tried other things. Some repairs/adjustments have made it better at the time, but it always seems to come back.
Yesterday started working on it again. Checked my AMM, and resistance for the heated wire was 3.2 ohms. Spec is 3.5 - 4. Is that enough difference to have bad performance, need of new AMM? Also, range of idle potentiometer went from 0-974 ohms, not all the way up to 1000.
Also discovered that with outside temp at 52, the airbox shutter was in all hot position (fresh air port closed), and I think it should be below 40 to be in that position. I took it out and tested it, and the thermostat does change, but I had to blast it with a hair dryer to get it to close off the preheating tube. I think that's out of spec, and it's probably been running too hot for the AMM. I put a little wood block in place of the thermostat valve to hold it in the all-cold position (preheat port closed) while I wait for a new shutter thermostat to arrive, and the car seems to run better. Could I have fried the AMM with too hot air blasting on it for too long? Or could out-of-spec temperature coming out of the airbox be causing it to run that rough?
Taking off the AMM, I also discovered oil in the flex tube between the throttle body and the AMM, enough to puddle in the corregations, but not enough for it to be in the AMM. What does that mean? Doesn't seem good to me, but I don't know what possible problem that indicates.
Many thanks for any ideas or information.
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