Hesitation at closed throttle

[FinalD]

Partly following on from this thread where I changed the TPS for another I had.

When driving around the car seems to hesitate/not pick up properly when I'm off the throttle and apply a small amount of throttle (or go no throttle to WOT even).
I'm guessing this is due to the TPS being dodgy as once the throttle is opened it goes through the revs fine.

Occasionally (very rarely but it does happen) the car will over rev/rev up a bit when off the throttle to change gears, it doesn't usually really climb, just doesn't drop, might go up by like 50-100 rpm, this is at ~20mph around town. But as I say, that is very uncommon, but does happen.

The ICV whines fine and as far as I know everything else is working fine, it is just an odd issue and makes town driving a bit annoying.

I also find that I can't pull away from a stop easily with low/idle rpm, I need to blip the throttle a bit to ensure that once away I can climb the revs without the hesitation from closed throttle to open.

The car is a facelift engine m20b25 325i.


E: Also to add. The revs don't drop to idle straight away when stopped in traffic/at lights etc. they will drop to ~1100rpm with clutch down and then only drop to ~800rpm when the car isn't rolling at all...that I find very odd.

[Brianmoooore]

You will get hesitation like you describe if the gap between moving the throttle plate off of its stop and the TPS switching is too great. It's not enough to set the TPS so that it switches when the throttle is pressed; it has to switch immediately the throttle moves.
With regards to your idle speed when rolling. The instrument cluster sends a speed signal to the engine ECU so that it knows if the car is actually idling or still moving with the clutch down. The dual idle is as it should be, but it does sound as if driving technique could be improved.

[bm1956]

Hi FinalD

you may need to remove the throttle housing from the inlet manifold and check that the throttle switch is working as it may be that its been adjusted wrong it also sounds that it may have a air leak

[FinalD]

You will get hesitation like you describe if the gap between moving the throttle plate off of its stop and the TPS switching is too great. It's not enough to set the TPS so that it switches when the throttle is pressed; it has to switch immediately the throttle moves.

&

Hi FinalD

you may need to remove the throttle housing from the inlet manifold and check that the throttle switch is working as it may be that its been adjusted wrong it also sounds that it may have a air leak

I've not adjusted the TPS (not intentionally anyway) so you're saying it's likely to just be a case of it being slightly misaligned causing it to not respond properly? That's fine then, I can remove the throttle body and have a look at adjusting the TPS (with the cap off so I can see what is going on with regards to the micro switch).

With regards to your idle speed when rolling. The instrument cluster sends a speed signal to the engine ECU so that it knows if the car is actually idling or still moving with the clutch down. The dual idle is as it should be, but it does sound as if driving technique could be improved.

Oh ok, that's fine then.
I'm used to more modern fuel injection engines in the Mk3 Mondeo and the E36 (M52 and M44) which either don't have it, or are more subtle about the way it works. I'll just need to worry less about it and learn how to drive to the engine.

Cheers for that, both of you.

[Brianmoooore]

If you've changed the TPS, then you've 'adjusted' it, but not necessarily correctly. It has slotted mounting holes, which allow it to turn slightly relative to the throttle shaft.

[FinalD]

Yeah, I removed and reseated it and did wonder about the fact that it has the slotted mounting holes. That's what I mean about not intentionally adjusting it, removing and refitting must adjust and I obviously didn't ensure that it was fitted/adjusted correctly.

Fairly simple fix then, certainly beats buying a new TPS.

[Brianmoooore]

Take the whole throttle body off, loosen the TPS fixing screws and adjust it until it reliably clicks as soon as you move the throttle of its stop, consistent with reliably clicking back again when you release the throttle.

[FinalD]

Just to update this.

I adjusted the TPS so that when you breathed on the throttle it clicked pretty much, so instant response in theory. It still wasn't running right and on a ~3mi trip it went from a cold start idle of ~900rpm to a warm sat in traffic idle of ~1800rpm. It was also kangarooing when WOT as if it wasn't sure what the throttle was doing.
Something was obviously wrong and I had previously tested the TPS and WOT didn't give a signal. As the sensor was old and unknown I bought a replacement which appears to have sorted all of my problems. Throttle response is near enough instant (much more what I'm used to with newer cars), clean ~800rpm idle and no kangarooing at WOT.

Cheers for the advice and help.