Sticking throttle ?

Hi, I have a MY 2000 fly by wire 525i manual 107K which has the following intermittant problem.

On occasion I get zero engine braking, with my foot clean off the gas pedal I can put my foot on the clutch and the engine revs just sit up where they were for several seconds before finally falling away slowly, can take fully 7 seconds for them to drop to idle and it then sometimes stalls or hunts up and down. This doesn't happen when the engine is cold and doesn't happen in slow moving traffic but does happen intermittantly on the open road during the warm up cycle and when fully warm. When the car is playing up I can pull over and stop and reproduce the fault by simply reving the engine. It can sit right up at 5000RPM so I don't think it is an air/vacume leak.

I have done the following removed the throttle assembly cleaned it out and removed the cover to the stepper motor all seems to work smoothly. Removed and cleaned out the ISC valve and all seems to work smoothly. Replaced the MAF. Throttle pedal seems to work smoothly.

Could the fault be due to a deffective oxygen sensor ? or the PCV valve ?

I know the DME controls the rate of closing the throttle butterfly to reduce emmisions, is this simply a pre-programmed rate or is it a closed loop system with inputs from temperate and oxygen sensors ? i.e. could a defective oxygen sensor giving a high/low reading cause the EMU to close the throttle butterfly real slow ?

I am afraid I don't have an ODB2 tool to pull the codes but guess this is the next step if no joy here.

Any help much appreatiated cheers Ben.

Reply » Sticking throttle ?

You said you cleaned the ISC valve...I would normally call it the ICV (Idle control valve). Just checking as that was my initial thought.

Also, the 525i should be a 2001 model year, not 2000...IN THE US (I see you are in the UK).

Other than that, I'm not sure what it could be. Checking codes would be my next step or a dealer or independant BMW mechanic.

Reply » Sticking throttle ?

Hi Thanks for the help yes I meant ICV.

I think I will blank this guy off and take the car for a spin just to double check.

Then I guess I will order a ODB2 tool and seee if there are any codes.

cheers

Ben.

Reply » Sticking throttle ?

Let us know what you find out, Ben.

I would say that an O2 sensor or the MAF could be next on the list to check out.

Reply » Sticking throttle ?

Well I took the plunge and bought an ODB tool and read off the codes only one a MAF code which must have been left over from before I changed it, I cleared the fault and it has not come back. I have done a bit more diagnosis to narrow down the fault.

Disconnected the MAF and ran the car no change
Disconnected the 2 pre cat O2 sensors and ran the car no change
Blanked off the Idle Control Valve and ran the car wouldn't idle at all but still had the poor engine braking

So I traced the wires that drive the throttle butterfly valve stepper motor back to the DME and connected up a multimeter at the DME. Under no load it reads 5.25V reducing to -2.5V as you step on the gas when the car is playing up you can see that the DME is driving the valve. ie When working correctly if you rev the car to 5000RPM and take you foot off the gas the reading returns to 5.25V within a second. When the car is playing up when you take your foot off the gas at 5000 RPM the voltage slowly increases from -2.5 up to 5.25V in line with the rev counter this can take many seconds.

It is definately a problem caused by the DME keeping the throttle valve open. Why is it doing this ? the carbon tracks on the throttle butterfly look fine and read sensible resistance values I checked these back to the DME as well.

Could it be the throttle pedal itself ? The fault doesn't seem to be linked to the mechanical action of the pedal ie blipping the throttle never clears the fault. Does anyone have the wiring details for the pedal ? I can trace the wires back to the DME but don't know which ones are which. ?

Another fault appeared yesterday for about 20 seconds the CEL came on, the speedo went to 0 the ABS light came on and the MPG gauge went to the stop. Is this an ABS sensor presumably the one the DME uses to determine road speed ? The fault then cleared all the warning lights went back off and when I conected up the ODB tool there were no codes either :-(

I think I am going to have to bite the bullet and take it to the dealer, first time in 20 years this is not only just going to hurt my wallet.

cheers Ben.

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