Engine/acceleration question

[Jzza4]

While driving (30-55mph), the car hesitates around 3000 rpm when accelerating, but stops if I continue or reduce speed. What could be the reason?

I have changed the spark plugs, oil, air filter. My thoughts are the fuel filter or pump.

[genphreak]

While driving (30-55mph), the car hesitates around 3000 rpm when accelerating, but stops if I continue or reduce speed. What could be the reason?

I have changed the spark plugs, oil, air filter. My thoughts are the fuel filter or pump.You might need to check your Air Flow Meter (AFM). It has atrack that wears; helps to clean this. You can measure its resistance with a multimeter by disconnecting the AFM and opening the flap that opens inside it as the engine draws more air through the intake.

Easy to remove with an 7, 8 and 10mm minisocket a ratchet. Take it off and turn it upside down, as so excellently detailed here (http://paulaxford.com/bmw730i/afm_service.htm). Be careful to make sure the vacuum hoses running off the intake manifold are not leaking air (this can cause problems too), replacements are a good idea if this is likely. Do not overtighten as the aluminium can fail under pressure and engine heat if so. Just make sure surfaces are clean and smooth when reassembling the pipes.

Also check for other intake vacuum leaks- the pipes that run to the Fuel Pressure Regulator on the Fuel Injector rail from under the intake manifold are always worth replacing. Pipe must be 4mm I.D. heat and oil-resistant hose, you will need a metre of it (3'). :) Nick