revs dipping

[rstrysull]

Just a quick question. When I come up to a junction for example,just before the car stops the revs dip to about 600rpm and then jump to about 1000rpm before settling at about 800rpm--is this normal?

[Shoppinit]

Nope. Mine doesn't do it.

[ecain63]

Throttle position sensor? Ask Grizz!!

[ecain63]

Or maybe torque converter is disengaging late.

[Shoppinit]

Could be, but I think there are other avenues to explore first. I think the first thing is to whack the vagcom on there and see if there are any DTCs. I'd be hoping to see a defect with the idle control valve or something similar.

[ecain63]

Is it idling badly at standstill? - say after 20 secs or so at the lights?

[rstrysull]

no, when it settles down its idling sweet as a nut at about 800rpm. Its just when you are on the overrun approaching a junction for example. You think the car is going to cut out but the revs drop to about 600rpm the suddenly jump to 1000 rpm and the settle down to 800rpm.

[ecain63]

Hmmmm. That is odd. Sounds like something is resisting the engine hence my gearbox idea.

[paul_23]

Mine occasionally does it after a fast stop from 4th or 5th gear after a long drive.

Is it worse or more regular when you come to a fast stop - if yes then it is probably a gearbox issue and probably torque converter delayed unlocking. If you log blocks 2, 7, 9 (I think) in VAGCOM under transmission you will see the gearbox and TC behaviour - it tells you if the TC is closed or open - if you slam on the brakes and stop when the TC is open then it probably wont do it, but if wait till it shows CLOSED then it is more likely to do it and basically the engine revs are being dragged down by the closed TC and then recover when it starts slipping (open).

Not sure if it is a fault or not, just a limitation on how quickly the TC can react and what it's stall speed is (ie the speed it starts slipping again). My previous V8 S4 was bad at this and felt quite jerky so some cars do it but others don't.