Hesitation when moving at idle speed - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 10-20-2010, 01:09 PM
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Lightbulb Hesitation when moving at idle speed

Have a 2008 750li with 28,000 miles. It now hesitates when moving at slow speeds, forward and reverse but throws no codes and the hesitation is intermittent. At 65 mph, when you accelerate to 70 mph slowly, it feels a little rough, but then is smooth. More noticeable when going up a hill.Dealer has replace the transmission and the problem do not change. Any ideas?
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#2 (permalink) Old 10-20-2010, 01:23 PM
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if it is still under warranty let them throw all the parts they want at it... if you want to try to figure it out id suggest starting with a throttle body clean up (i think you car has 2??) cus if you havent been using premium gas they get real nasty. if your are going to do this make sure you disconnect the wires going to the throttle body actuator before starting or it will mess up the alignment between the pedal resistor and the throttle body actuator. throttle body cleaner can be bought at any autozone checker or napa...
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#3 (permalink) Old 10-26-2010, 02:18 PM
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Yeah, umm, gas doesn't affect the throttle body. This is a "dry" system; dust/ dirt/ air go thru the filter, thru the throttle body, thru the manifold, thru the valve ports. The only "wet" part is from the injectors downward. I'd agree with a cleanup, along with a bottle of Seafoam or Techron in the gastank at the next fillup. Check the hoses, also: a minor vacuum leak can cause the same symptoms.
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#4 (permalink) Old 10-26-2010, 03:08 PM
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Seems like a vacuum leak would show up all of the time, this problem comes and goes. I'll try the clean up.
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#5 (permalink) Old 11-01-2010, 11:30 AM
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> Seems like a vacuum leak would show up all of the time, this problem comes and goes.
I'm an old fart, and I've found that the more you define the problem, the more you define the solution.
You could have a small leak, that shows up more often at times of more vacuum. There's been a lot of postings of rough idling and the engine acting up when coasting down a hill- all symptoms of a vacuum leak at high vacuum situations. When you step on the pedal you get more air ~ less vacuum. If the air/fuel ratio isn't right you may be getting an occasional misfire.
Then again, there could be other causes. Dirty injectors, a small head gasket or manifold leak, a bad O2 sensor, a misadjusted TPS, a loose spark plug wire or a misfiring spark plug. And many times it's more than one thing.
> I'll try the clean up.
Do the easy/ cheap/ free stuff first. Then check the next level of potential problems and parts. At least you can cross them off the list.
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#6 (permalink) Old 11-01-2010, 12:02 PM
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Had the BMW Area rep drive the car last Friday. He said that the BMW was such a high quality machine that this is now the way they run - rough at idle and lug when you accelerate slowly. Nice to know that I spent $30,000 more for a used BMW than I spent for a new Avalon and the car runs like @#!%.
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#7 (permalink) Old 11-10-2010, 10:15 PM
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Plplplpl. What the area rep REALLY said was he don't know, he don't want to know and he don't want to pay to find out. My rough idle went away after the second bottle of seafoam. Mine will also lug a bit if I'm in "D" in the city; it does run better in "3".
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