I have an e46 BMW and I recently noticed a problem which hasn't occurred before. While at a stop if I turn on the rear window defroster I notice that the engine idle RPM starts to stutter (goes down a bit) and then goes back to normal. Is the extra load sapping the spark plugs momentarily? Increased alternator load making the engine work harder? What could cause this and should I be concerned about it?

  • Check your battery connections and remove and clean them is necessary. – Moab Feb 11 at 17:47
  • If the temperature is cold (ambient & engine) then the ecu may take a second or two to compensate the new load on the engine - happens on mine but fine once warmed up. – Solar Mike Feb 11 at 18:11
  • if the same happens when you turn on the headlights-heated seats-other high current aplications then it is normal it is just the engine adjusting to different load at idle. – trond hansen Feb 11 at 20:27
  • @trond No only seems to be rear defroster. – TheSlavMan Feb 12 at 22:00

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