Hey guys,

i know this is going to be wierd, here is the deal. My car, 1989 760ti would run for a while and i could drive it fine w/boost. Then you shut it off start again and the rmps go wild( 300-1500rmp) and then car stalls out. So i replaced the amm with a newsed(new to me but used) and the car would be drivable except under boost it would run way too rich and blow black smoke out the tailpipe. I then replaced the fuel pressure regualtor and the seals on the turbo-bypass valve. I also got a new hose for the fresh air intake and a new pcv thing(opaque white hose connector mine was so clogged and the little nipple broke of). OK so here is the deal, if i put in the old on I can drive with boost but then it just randomly goes crazy. However if put in the newsed one then i can drive it all the time except i cant let the gauge go to the white otherwise it bogs down and starts shakings and black smokes pours out the pipe. I'm soo confused and i dont want to take it to a mechanic but it seems very tempting now. ANy suggestions, this doesnt seem like an air leak because of the way the two amm behave diiferently

BTW both are the same model number(amm)

Do you have any air leaks (holes, cracks) in any of the intercooler hoses? The most common hose to check is the one from the MAF meter to the turbo at the turbo (bottom front) as it often crumbles in time from oil deterioration (disolves the rubber). If it's NG, it must be replaced and its not cheap (about $135).

I agree that the symptoms suggest an air leak. Off boost or at idle, an air leak will throw off the fuel/air mixture and the idle air valve will try to compensate but has only a limited ability to do so. The result could be the bad idle. The interesting thing about air leaks is that they are not always constant; the hole may not open all the time. Check carefully.

On the boost, the symptoms suggest a big air leak. Too much airescapes for which fuel has been metered. The result is an over rich condition. Check carefully all big hoses. But also the little ones. The idle air valve hoses can crack and you may not see the split unless you remove and inspect the hose, particularly the one that loops through the intake.

AMMs can have problems in the harness just before the AMM. Right around where it bends sharply. Sometimes wiggling there will stabilize things. If so, you need to splice in a new harness end. Sometimes the terminals can dislodge also. Pull back the boot to inspect. Clean the terminals with deoxidizer spray.

I am not sure you have two separate problems. Maybe one problem with multiple symptoms.

Philip Bradley

A crumbling wiring harness can make wild things happen (like a racing blower fan). Also, a bad idle air control valve (I am fighting a 2500 RPM villian on my '86 244/B230F)

Finally, check for air leakage after the AMM.

This all assumes a clean throttle body.

Got a third?

Sorry, don't know enough.

Rene