Loss of throttle response

[John223]

Car is a 2003 Z4 2.5I E85 5-Speed manual 74K Miles

When cruising along in 5th gear, around 55mph, I punch the gas to pass another car and I get no response from the accelerator pedal. No response at all for about 4 to 5 seconds. No cell or faults lights. The RPM's do not increase, so it's not the clutch. It does not stumble, stutter of feel like a loss of power, so I rule out plugs, coils and maf. It's intermittent and has only happened about 3 times in the last month. The cars RPM's do not decrease, so connection is not lost. It's only happened in 5th gear, so not likely to be throttle body or TPS, which I would think would present itself in other gears. So at this point I'm baffled. I've googled most BMW forums and not found anything similar except here, but no resolution was posted. Any help would be appreciated..

[Monkeydonkeyratmagic]

Does the power pick up at just over 3k rpm? Would be a more helpful indicator rather than time based.

[John223]

Sorry for the delay in getting back.

The answer is no, because there is no increase in RPM. I step on the gas pedal and nothing happens. The RPM stays where it previously was, and acts like I never tried to accelerate. If I leave off the gas, it will slow down. I'm now wondering if its a throttle body issue or an accelerator pedal sensor problem. I've never had drive by wire issues before.

[ph001]

Wow, this is a strange one! As you say it only ever happens in 5th gear, this would seem to eliminate throttle body and accelerator pot. In fact it eliminates just about everything!

I think you need to be absolutely certain it doesn’t happen in other gears. Can you try cruising around in 4th for a while at the same rpm (so slightly lower speed) and see if the problem ever occurs?

[John223]

I can't for certain say it doesn't happen in other gears. It's only happened 3 times in the last couple of months, each time in 5th.

[ph001]

In that case I can almost certainly say it's nothing to do with your gears and it's just coincidence you notice it in top gear as that's where you spend 90% of your time. The M54B25 has two throttle potentiometers on the pedal (one for throttle position and another for throttle rate) and another two on the throttle actuator on the engine.

I would guess that one or more of the sensors are not correlating so the ECU does not trust their reading so will not apply a signal to the actuator (it is done this way by default for safety reasons).

OK, first thing to try is throttle adaption reset:

1) Sit in car with ignition off
2) Switch ignition to position 2 (do not start engine) and count 10 seconds.
3) After 10 secs, switch ignition off but leave key in. Count another 10 secs.
4) Start car as normally and go for a drive to see if it's fixed the issue.

If not, you will probably either need new throttle position sensor/s on pedal or on actuator. Hard to say which but a good diagnostics software should tell you.

[John223]

I'll try doing the adaptation/reset as you suggested. It might take a few weeks for it to occur again. I'll have to wait and see.

Btw, shouldn't a TPS or Pedal sensor problem trigger a service engine light? Or would it be the kind of fault that's stored internally and not indicated by the dash light?

Also, is it possible that the problem is with a brake pedal sensor or switch?

[ph001]

Few posts on this happening on the E46 325i which is same engine as yours. Nobody reports engine management light coming on. Should store a code though I expect.

I can't see how a brake pedal switch could be anything to do with it.

[John223]

Brake switch - doesn't stepping on the brake, while in gear and accelerating, deactivate the accelerator pedal on drive by wire cars? I've read this, but I'm currently away from my car for several days, so I can't test. Just wondering, because if true it would cause the condition and not throw a code.

[Piper1]

This is sounding a lot like my issue you revived a post about by mistake. Only difference is mines auto. Mine had gone away then came back a few years ago and still periodically does it. Though last couple of years it’s had way less drive time. I ruled out gearing, when it happened I tested out down shifting and revs changed to the lower gear but still no throttle response during the change. And no codes have come up with any of this. And the same scenario it only happens when cruising then you happen to want to get on it, ie. to pass.

The adaption throttle reset doesn’t apply for my situation (though did it anyway and still occasionally happens) since I always have sport on and if I’m not mistaken the throttle adaption only applies when in non sport mode.

Per a few suggestions in my old thread I have on order a new maf (mine needs replacing due to the hold down tab breaking) and vanos solenoids since I had to order some more goodies figured might as well (and now higher mileage then before).

I also have thought about replacing the pedal and the sensors that go with that if it still occurs after all this.

Besides those ideas I’m somewhat at a loss of ideas as well.

[ph001]

My car certainly still accelerates when lightly pressing brake but different engine to yours.

[Scooba_Steve]

I had a hesitation at almost the same speed and throttle position each time, turned out to be a VANOS solenoid. Worth reading codes as that was in there stored.

[John223]

I had a hesitation at almost the same speed and throttle position each time, turned out to be a VANOS solenoid. Worth reading codes as that was in there stored.

But was it always happening or a few times a month. And was it a bogging or completely inactive pedal?

I would suspect a Vanos valve problem would result in a bogging hesitation, not a dead pedal.

[ph001]

Yeh, I don't think the OP would describe this as a hesitation at all. It's literally seconds of no throttle response whatsoever. Has to be lack of throttle actuator operation for one reason or another (I would place a very small bet on non-correlation of throttle pots on pedal).

[Scooba_Steve]

Mine was a hesitation but just throwing it out there. In normal operation the throttle is fully open with power controlled by lift and timing.