Eratic revs when starting up

[danyeates]

Hi,

My S4 has been fine since I bought it, however, recently it's been revving 3 or 4 times, quite high and very quickly, just blips when you start the car up. Haven't had any throttle depressed when starting.

Also, sometimes the idle is a little lumpy, but it's not that bad, not bad enough to be a problem, it's the strange revs when starting that annoy me.

Any ideas on what it could be?

Thanks,

Dan

[Blue_Thunder]

Could be your MAF on the way out.

How does it drive on throttle?

[danyeates]

Hi,

Thanks for the reply. It seems to drive fine, although I have never driven another S4 to compare it to. It has a couple of times hesitated when I've been cruising at low revs and then put my foot down, kind of slight mis-fire but not that noticeable and it's only happened a couple of times.

Idle is fine, the slight fluctuation in revs is only slight, not really noticeable on the tacho, but you can feel it and hear it slightly. It seems to idle at the right revs.

If it is MAF, how much are they, I'll do a search, but just in case someone knows off the top of their head!

Thanks,

[danyeates]

One other thing worth mentioning, this last tank of fuel has only average about 18mpg, (just driving to work) I normally get ~ 24-25mpg which would suggest an intake problem I suppose

[Mike159]

I believe the exchange unit at audi is around £77. You will want to do this as the unit on its own is rather expensive. Very simple job so could be done in the dealer carpark or if its a friendly one no doubt one of the techs will do it for you if they are quiet.

[danyeates]

Right, well I'm going to change the temp sender anyway as it's cheap and it's been recommended I should just change it as a matter of caution. Is ther anyway of telling whether it's the early or late type sender on a 1999 T S4 (facelift), or do I have to go outside and pull it out to check the colour? Also, where is it?!

[danyeates]

Ah, another thing after doing some research, if I change the temp sensor, will this affect ym after run pump modification? I understand the modification uses a different Audi sensor, or is this a different sensor altogeher?

[s4-99]

Ah, another thing after doing some research, if I change the temp sensor, will this affect ym after run pump modification? I understand the modification uses a different Audi sensor, or is this a different sensor altogeher?

Changing the Temp sensor will not affect the after run pump mod as it is a different sensor.

The temp sensor is on the driver's side of engine as you look at it and ARPM is on the passenger side.

Have a look at this thread http://www.rs246.com/index.php?name=PNp ... ic&t=70869

[danyeates]

Thanks mate. Found it and have a replacement square type one on order.