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84 5000 idle drop

Non-turbo, 5-speed, runs great including warm up phase. Idles perfect at about 850 - 900rpm at normal operating temp. Issue: When idle comes down quickly from higher rpms, such as pressing clutch when coming to a stop or simply from reving the engine when stationary, idle drops to about 300rpm, almost stalling, then recovers to 850 -900rpm. This version is without a dashpot, so I'm somewhat confused as to why this is happening. Any suggestions would be appreciated.

Reply to
very_audi_5000
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I had this same symptom on a '91 100. It turned out to be the idle actuator switch on the throttle body not making contact at idle. This switch tells the ECU that it is either WOT or idle. When idle the ECU and idle stabilization operate the idle stabilization valve (ISV) to maintain idle speed. On the back of the throttle body there is a plug with three wires, one is ground the other two mak contact when it is either WOT or idle. Use an Ohm meter to check if it is making contact when the linkage is at idle. If it isn't there is a small adjuster with a lock nut that corrects it.

If it is making contact correctly you probably have a dirty sticking ISV that can be removed and cleaned with brake fluid. You may want to check the tech section for the T44s on Audi world to be sure what cleaner to use. I think brake fluid is the choice by not sure.

In my case adjusting the switch on the TB was the fix.

Reply to
TonyJ

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