Revs / Idle Problem

Guest · Nov 5, 2003

When I start the car up in the morning it revs itself up to just under 2k revs then drops down to normal revs - does anyone know what this might be ? I dont go near the throttle when starting.
A local specialist suggests MAF or Oxygen sensors. An associated problem (I think) is when pulling away in a lower gear than maybe normal (example is going over speed bumps in second gear at around 3-4 miles an hour - or a rolling start in second gear) the revs drop then bounce back up. This can make driving in traffic a little jerky.
Its a 98 996 with 35,000 miles on it & I know idle on earlier cars is altered by the aircon - but either on or off the revs seem to drop down quite a bit then back up before settling.

Any ideas ?

Julian.

tim court · Nov 5, 2003

I have the same problem when pulling away and the revs drop off..... sometimes to nothing which is a tad embarassing [

]

Have had it checked out but all faces are blank.......

Another 98 (99 model) 996 with 50k on the clock.....

Guest · Nov 5, 2003

This is what worries me in a way - they are talking about relpacing the MAF - see if it cures it - then if not replacing the oxygen sensors.
All that is quite an expensive job with no guarentee of curing the problem.

Grant · Nov 5, 2003

All 996's idle faster on start up for the first few minutes/seconds when cold, but usually start at around 11-1200 revs dropping to 800-ish, 2k does sound too high !!

With regards to the part throttle take-up all 996's seem to do this, if you lift
right off the throttle & then only apply a light opening it pauses & can be jerky, my OPC tells me it's all down to the engine mapping for fuel economy, but it can be a pain in stop start traffic!!

Guest · Nov 5, 2003

Thanks Grant - yep when you start from cold it revs right up to 2k then drops to normal.
Even if the other stuff mentioned is normal I need to get this looked at as - apart from anything else - its embarrasing, people think I am revving the car when I am not !
Oxygen sensors seem to come up time & time again so will get these looked at.

Guest · Nov 5, 2003

Hi, I can confirm that this problem does occur on 996, having experienced it myself, however, due to having completed 90K miles it is understandable.

Same situation, oxygen sensors, mass air flow senor (MAF) being bandied around, plus catalytic converters, so with the help of the extreamly expert service guy's at our OPC (Rivervale in Portslade, Sussex), in particular, Peter Roe and Paul Gilbert, we set about removing and replacing all of the above......the cheque book was steaming and so was I, with the problem still unsolved, when leaving the car with them, being driven with the lap top plugged in on the passenger seat it was noted that the engine stabaliser was giving out different readings to the position it was at, giving over-reving, fluctuating tickover and stalling, no matter what the aircon was doing....
changed and problem solved.......hurray!!!!!!

It may or not be the same for your cars, but the stabaliser I beleive is one of the cheaper items out of all the above, if only we knew that at the start....but someone had to be first, and as usual its me......

tim court · Nov 6, 2003

Allan,

Could you advise how much the stabiliser part was of your final bill???

Guest · Nov 6, 2003

the start up "blip" has puzzled me as well As Grant says it does appear to be normal (though I am closer to your 2000 rpm rather than 1100 rpm and with a later model)

ClubSport 911 · Nov 7, 2003

This "high idle" is easy. Many cars have a cold start idle program which detects a low ambient and gives a fast idle to warm up the catalyst in the shortest possible time - thereby reducing emissions

This explains why "sometimes it does it and sometimes not"

Many cars I have owned do it, and working as I used to in the Software and Automation business (and therefore associated with every single car manufacturer) I got to ask a few bods...

They all have this "feature on certain models" - design dependant of course

Rgds

Steve

Guest · Nov 10, 2003

Thanks Steve & others who replied.
Car went to AFN Reading who were great - agreeing to see the car at short notice & run a full diagnostic on the car, they also kept it overnight.
They diagnosed a faulty MAF sensor & replaced.

They did say its a characteristic of the 996 to dip revs slightly at low speeds but mine was worse than normal.
Its now much better.

The high revving on start-up sounds - from what Steve & others are saying - normal......thinking about it, it only started doing it in the cold weather which makes sense.

Thanks all !

Julian.