Alrighty, I've got a problem which has suddenly taken a turn for the much worse. My car had been running poorly when cold, ie. crappy surging at cold idle, acceleration bad when cold. These symptoms recently started getting much worse. The car now dies around 10 times when started in the morning before finally warming up. I can keep it from dying at all but applying slight pressure to gas pedal. When driving while still cold, the engine runs very badly, doesn't accelerate well, hesitates and such. When its warm, the idle is still pretty bad, shakes the car noticeably, and dies maybe 30% of the time when I stop at a light. Running above 1000 revs, the car seems to run pretty good, but not great. Has decent power and such.

Checks I've done. I backprobed the O2 sensor while plugged in with engine running, and it was bouncing up and down randomly in the .1-.9v range. The range is acceptable, the O2 sensor is working, but I don't know if the bouncing is acceptable. Today, I uplugged the AMM, and the idle ran perfectly smooth. Of course it ran like crap above that because of the limp home mode, but the idle was very nice. Made me want to kiss the car. I'm guessing the AMM is bad. I checked the recommended terminals on it, and the heated wire terminal read like 4.4 ohms. The haynes says it should be 3.5-4.0. Would this reading be so far out of spec as to warrant replacement of the AMM? What are your ideas? Thanks for the help!

A computer controlled fuel system needs three items to run well at ALL times. It may not run within emission standards but will be cloer over the longer period than a carburated engine.

These three:

Constant set fuel pressure. Controlled by fuel pressure regulator.

Known mass of air. Measured by the AMM.

Temperature of environment. Sensed by the ECU Temp sensor.

To do it well, there must be NO EXTRA AIR ENTERING THE SYSTEM AFTER THE AMM. ie NO VACUUM LEAKS ANYWHERE.

The 02 sensor only serves as a means of balancing variances between the three after the combustion has occured. Like waving your arms to direct the horse after you've opened the barn door.

By disconnecting your AMM at idle, your ECU defaulted to a fuel delivery rate (injector pulse rate) that would make an engine run at "normal" temp based upon the pre-calculated amount of air that the engine would pull in at a predetermined RPM. This set up would not respond WELL to changes in RPM, but would run at all RPM ranges.

Based upon the above, I'd say that disconnecting an AMM indicated a fuel system functioning within tolerances and a fairly leak free engine air delivery system, but does not rule out the AMM misreading the amount of air being drawn into the engine or an incorrect reading temp sensor.

One down two to go. Which one? Since you have a meter:

Check your temp sensor for the ECU tucked up under the 3rd intake portion of the intake. Get a Bentley or Volvo Service manual and check its resistance at the ECU connector. This check point also checks that a signal is getting to the ECU through the wires. You may be flooding out with an always cold engine (very high resistance) or leaning out with an always hot engine (very low resistance) according to the sensor.

For those without a meter or just part swapping until the problem goes away; the temp sensor is a lot cheaper than the AMM but does not check the wires in between. Opinion, R&Ring two of the cheaper temp sensors makes me wish it had been the AMM!

AMM reading may be just your meters tolerance variance. My 83 has a similar "out of spec" value but I'm having no trouble starting or keeping running. Another friends 83 that was hard starting and running rough finally corrected itself after he changed the temp sensor after sticking in one of my known good AMM and did not change the problem.

Also, your idle control valve may be sticky or non functioning but how that would affect engine running I cannot fathom. The air has already been measured and is just taking a different route to the same place.

Due to computer problems, I missed the start of the engine mount thread and am too lazy to go back and read all of them. So in the spirit that that thread has instilled:

This is a disclaimer to disclaim the disclaimer which disclaimed the disclaimed. Or as Schult'z of Hogan's Hero's so aptly put it: "I know Nothiiing!!!"

Duane, thanks a lot for the extremely detailed post. I checked the coolant temp sensor this morning. It reads fine resistance at cold and hot temps. I've done the vacuum leak and air control valve tests too. They're fine. Just to be certain how it felt, I once again unplugged the AMM today to see how it idled compared to having it plugged in. It runs immesurably better. The car doesn't shake at all, and the idle is stable and smooth. When it's plugged in, the car trembles intolerably, and the idle fluctuates slightly.

I checked the AMM again today. The book says the heated wire resistance should be 3.5-4.0 ohms. Mine read 4.2 today. The idle potentiometer resistance should be between 0-1,000 ohms, and should vary accordingly when you adjust the screw next to it. This checked out fine. Would you happen to know the correct idle mixture number? I think its like 700 ohms but am not sure.

Any other ideas? Thanks a lot for your help.

Out of interest which terminal numbers are for the hotwire? is there any more that can be measured with a simple meter.

Bill D.

Isaac -

Make sure the injector seals are not leaking. Buy a spray can of Gumout, and spray the area around each injector/manifold interface (liberally) one at a time. If the idle increases noticeably, then you have found the problem. If not, look for other vacuum leaks, particularly the inlet snorkel ( esp. where it rubs against the fender).

Gary, thanks for the idea. I have already done the spray test on every seal and gasket. Last week I changed a leaky injector seal, and this did nothing. None of the others are leaking.

Have you checked the obvious, cap and rotor, if bad or hairline cracked they would cause similar problems. If you are using anything other than Bosch get rid of it and put in Bosch. Had a similar experience with and 84 and ended up changing my timing belt in a gas station parking lot. With the new belt it still ran like crap. Found the problem to be a bad dist cap, it was something other than a bosch and not even a year old. I learned to use nothing else but Bosch parts...... Tom 240aholic

Tom, I can't agree enough on the Bosch cap & rotor. None of the parts guys near home stock Bosch, so more than one I've had to settle for the black stuff - Standard? Anyway, once I put in a new non-Bosch cap and rotor, and the car refused to start until I put the OLD Bosch rotor back in. Now I always keep a retired cap & rotor set on hand for emergencies.

Also, to second your point about "checking the obvious." I recently acquired a nice '92 245, and am still giving it the full going over. New shocks, IPD bars, fresh filters, etc. I noticed that although it starts easily and runs well in the morning, driving home on hot days there seemed to be an intermittent miss, more like a lean surge condition. All vacuum lines are OK, and I started envisioning a long journey through the fuel injection system, computer, ignition module, and so on. Well, in preparation for this weekend's timing belt change, I threw on the new cap, rotor and ignition wires which have been sitting in the FCP/Groton box in my mud room for a few weeks. The old plug wires nearly disintegrated when I removed them... and guess what, the "miss" is a-missing! Gotta remind myself to always cover the basics first.