My buddy's AMM's shot, however, I would like to put the AMM from mine in his just to drive around for a while. Can this ruin my AMM? I baby my car, and he doesn't....so I am little worried.

TIA!
SM
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90 BMW 325is, 98 BMW 528i, 90 Volvo 240DL

also ensure the ignition is OFF before you disconnect and connect the AMM

If they are the same AMM this is OK with one caveat. The most frequent cause of AMM failure is caused by a stuck thermostat in the air box. The too hot preheated air will then fry the AMM. This is possibly the cause of his failure. Check his airbox first or pull off the preheat hose.

I cannot think that his driving style could possibly hurt the AMM.

Very small, minute chance of harming yours as long as you make sure your buddy's AMM is the same type yours is. Your 90, I think, has the one ending in 016. Just make sure your buddy's ends in 016. The reference to a small, minute chance above is just my way of saying that it's remotely possible there's a fault with your buddy's wiring harness that could, say, short the output of the AMM to ground, or maybe his airbox tstat is long gone, I don't know. Very small chance.
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Art Benstein near Baltimore

You could hurt your air mass meter if his car has a stuck airbox thermostat. If his car is getting hot air all the time, that's what killed his AMM and that could kill yours. Before you run yours in his car, make him buy a new airbox thermostat. They're cheap and required when you buy a new AMM (or else you void the warranty).
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Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total