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Erratic idle on my 1987 Porsche 924s

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Hello! Time for a new thread here, it's been more than a year since the last one.

I picked up my '87 924s last fall, and have poured a fair bit of cash into it to make it a reliable drivable car. One thing that has confounded me a bit is the idle engine speed "bouncing" between ~ 925rpm and 1070 or so rpm, and the resultant whole-car-'shake' (my engine mounts are a bit tired).

This doesn't happen when the engine is cold. New plugs, wires, cap, rotor have not shown any positive effect. I've checked three times for a vacuum leak using the tried and true brake clean spray method- nada. I've poured some octane boost/ fuel system cleaner into the gas tank with some 93 RON fuel, it may be my imagination, but that may have lessened the idle variation to be somewhere between ~950rpm-1000rpm. Maybe just wishful thinking........

I'm wondering if the idle air valve needs cleaning, perhaps even replacing? Perhaps the throttle body is dirty at the intake? Maybe the MAP is done? Any thoughts or ideas will be appreciated!



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