Yesterday I had to drive a lot and after 100 miles I noticed that the idle won't go below 1500 rpm (should be 600) on my 1993 BMW 525i (euro model), except when I drove slowly in a high gear. This morning all seemed to be OK (only did a 5 miles trip though), maybe the rpm fallback was a bit slower than usually when releasing the accelerator.

On the other hand, earlier before I had to put some extra pressure on the accelerator to set it off from the top, unpressed position. Now it moves smoothly even from the top position.

Could this be just because the throttle adjustment screw is out of alignment?

  • 1
    Can you say what the year/model is of your vehicle is. – Allan Osborne Nov 22 '13 at 10:24
  • @AllanOsborne 1993 BMW 525i (euro model) – zeller Nov 22 '13 at 11:51

The throttle body at this age of vehicle has a real possibility of being 'dirty'. Take off the large hose connecting the throttle body to the air cleaner at the throttle body. If the visible throttle body parts are heavily coated with cruud, then clean the throttle plate and throttle body with a tooth brush and throttle body cleaner fluid. Operate the throttle plate to allow cleaning of both of its sides and edges. Why? As the engine warms up it causes the throttle body and throttle plate to expand slightly. The cruud(deposits) on the plate and body cause it to remain open instead of fully closing. This will cause a higher erratic idle speed and slow return to idle. The symptoms you have described when hot.

  • It turned out that the butterfly valve needed the cleaning. Thanks for the tip! – zeller Dec 4 '13 at 20:33

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