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Discussion Starter · #1 ·
O.K. Calling ALL wizards out there in Beemer land.
My 1995 325-i will sometimes refuse to come off idle. It has done this several times.
The car drives like advertised, come to a stoplight and when the green light goes on, the car will simply sit at idle and not respond to throttle imputs. The engine will not die,simply idle long enough to become a traffic hazard and agravate every horn honker in town.
I feel this is more than a nuisance, a safety issue because the driver is now another passenger.
Any ideas? The car does not have traction control. I know the traction control unit (if installed) will mimic a similar problem. These episodes last a few seconds, then it's like nothing ever happened. No codes register.

Thanks
 

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could be simply dirty spark plugs

Just a few thoughts:

Maybe engine needs a service, sometimes lots of gunk on plugs can cause hesitation. Is there a hesitation also when flooring the accelerator pedal while travelling at medium speed in 4th gear?

If there is a mechanical throttle linkage maybe it needs cleaning/lubing?

Could be O2 sensor is past its best?

Worst case scenario is worn piston rings. Is the car slower than usual to start up, an extra second of cranking required before starting fully? Had this problem on a non BMW which had previously had a water pump failure which caused engine to boil dry and rings to wear - there was only a minor loss of power at medium-high revs, but stalled very easily at low revs and coming off idle.
 

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Discussion Starter · #4 ·
This is a stomper.
There is no throttle by wire. The pedal is mechanically linked to the throttle body butterfly.
The car has had excellent maintenance.
This is not a start problem. Picture a normal drive, come up to a stop light and sit at idle until the light changes; when it does, the engine refuses to respond to throttle inputs for maybe 15-20 seconds. Then it will wake up and drive like it just left the show room.
There is no check engine light and no code to be read.
 

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You have a drivablility problem that a technician would love if your car was under warranty (read: bill BMW hours diagnosing) since it doesn't turn the engine light on nor latch an engine code there is no problem right?

Your car feels normal at idle and you depress the pedal and nothing, so I assume that you even mean that your pedal feels normal - free and easy to depress?

What you describe would make me think the throttle valve switch (throttle position sensor) is bad. Since no code is set, and the check engine light stays off the problem most likely is mechanical, and since the fuel delivery system is computer controlled and monitored with the exception of the throttle body's mechanical connection to the acc. pedal I would check the valve switch (which interprets how far the throttle body is open along with the air flow meter for the computer). But this raises several questions: Why does the defective switch not latch an engine code? and Why does this happen only after you have been idle at a traffic stop?

Now this is at least a $75 part new, so I would not just take my word but see if you can find a helpful dealer technician or reputable/trusted ind. mechanic and describe your problem to him/her and see if they remember anything like this from their past experience.

Also maybe you can find a low traffic area (good luck in FL right?) and try and get the car to repeat the problem, If it does quickly pop the hood and us the handle of a screwdriver (or something similar) to lightly tap the valve switch and jump back in and see if that remedies it, if that makes the car operate normally that is more evidence that the switch is bad.
 

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Discussion Starter · #6 ·
Thanks, vintageorange, wideboy, myE-36 there is nothing better than an intermittent problem that does not register a code in the compfuser.
If I remember correctly, the T.P.S. is a rheostat where you have battery voltage in and the opposite end of the resistor is grounded thru the computer. The swept terminal will read from almost zero volts to about 5 volts in proportion with the arc of the throttle. That checks out.
Another $$$$$ possibility would be the M.A.F.sensor. that would have to be a hard pill to swallow since I would be playing poker with parts and not really know because the car is being driven with a scanner plugged in and the last 100 miles tell the scanner that all is well in the home front.
The car is a low mileage car with great maintenance but the last year has been trying. A lot of little things pop up and are taken care of inmediately if not sooner. This driveability problem has me up against the wall.
Thanks again,for all your thoughts on this. maybe I can squeeze my knowledge bank for you guys some day.
 

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I just doubt if it is the MAF sensor because of the symptoms you describe... but this being such an unusual problem who knows... BMWs would be so much easier to trouble shoot if they came with a spare set of interchangable parts (especially the computer/electronic goodies).

Imagine if your neighbor had the same car: "Hey Chuck I need to borrow your mass air flow sensor for an hour tonight?"

Not poking fun at you, just I feel your pain, spending weeks diagnosing a bug that takes a $10 part and a couple of tie wraps to repair on an otherwise technically advanced mechanical marvel.

And I agree with you on your philosphy of not throwing parts at a car hoping to fix it.
 
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