'92 535 runs lean after hard driving

My '92 535 has lately had a strange issue. After driving hard, repeated WOT red line accelerations etc., it runs really lean after it has been shut off for a while. Last time it happened I nearly didn't make it
home; It would barely idle, and giving more than a little gas it would stall. I had to feather the throttle to keep the rpms around 2.5k and change my speed using the clutch. After I got home the exhaust system made more ticking noises than usual, looking underneath revealed orange glowing cats which can only mean it was running seriously lean.
Anyway, all other times the engine runs fine. I know the injectors are leaking and the AFM is a little off, but I don't see how that has anything to do with this.
Anyone experience anything similar?
Thanks, Ulf
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Take a look at your rubber intake boot. High rpm running would produce greater vacuum demands on the intake system and, at this age, that boot has gotten pretty hard. High vacuum may be pulling a crack open intermittently. From my E28 experience, I can tell you that they like to crack on the bottom, where you can't see it. Not so much from sheer contrariness, as you might think, but because that's the side that gets baked by engine heat and is brittle.
Two ways to diagnose:
The Cheap Way: Squeeze it vigorously while idling and see if the idle speed changes, either up or down, indicating the vacuum leak.
The Less Cheap Way: Spray flammable carb cleaner or propane in the area to see if the engine picks it up and idles faster when it sucks it in.
Good luck! HTH! -- C.R. Krieger Been there; done that
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E28 Guy wrote:

Excellent advice, C.R. It wouldn't surprise me if this is related to the rough idle when the engine is cold. Would be great if I could get everything sorted before I sell the car, and the new owner would probably appreciate it too... :-)

Ulf
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