Fluctuating revs

[911 dreamer]

Hi people, can anyone point me in the right direction with this please?

 

I bought my 1998 996 a couple of months back, it's carrera with the tiptronic box which I am learning to really like. The thing is it has this annoying issue; it might be in 2nd, for example, but it feels like it has two gears within one and it's quite noticeable - I guess these are modes but can anyone confirm please? Also, within a mile of so of leaving home I go through several 30mph limits, I slow down and it normally shifts down into 4th, there's not much load at all on the engine as it's a flat road - then I look at the rev counter and it's going up and down a bit and you can feel the revs hunting slightly. Incidentally, when idling it doesn't do this, it stays completely level at around 800rpm.

 

I've done the throttle adaptation by switching the ignition on for 60 seconds but I'm not sure that applies to cars with a cable operated throttle anyway? I'm planning to clean the throttle body but having looked at it it's quite clean already. Has anyone else experienced this?

 

Many thanks.

[JFP in PA]

Hi people, can anyone point me in the right direction with this please?

 

I bought my 1998 996 a couple of months back, it's carrera with the tiptronic box which I am learning to really like. The thing is it has this annoying issue; it might be in 2nd, for example, but it feels like it has two gears within one and it's quite noticeable - I guess these are modes but can anyone confirm please? Also, within a mile of so of leaving home I go through several 30mph limits, I slow down and it normally shifts down into 4th, there's not much load at all on the engine as it's a flat road - then I look at the rev counter and it's going up and down a bit and you can feel the revs hunting slightly. Incidentally, when idling it doesn't do this, it stays completely level at around 800rpm.

 

I've done the throttle adaptation by switching the ignition on for 60 seconds but I'm not sure that applies to cars with a cable operated throttle anyway? I'm planning to clean the throttle body but having looked at it it's quite clean already. Has anyone else experienced this?

 

Many thanks.

 

When was the last time the Tip was serviced?

[911 dreamer]

Good question - it's done 90k, all services at Porsche/specialists inc. brake fluid chane but I can't see anything to do with the Tip, do you think that's it JFP?

[JFP in PA]

Good question - it's done 90k, all services at Porsche/specialists inc. brake fluid chane but I can't see anything to do with the Tip, do you think that's it JFP?

 

If you have no record of it being serviced, and the car has 90K on it, you are way past (2X) when we would have serviced it.  You rev fluctuation could be slight slippage in the converter or gearbox.  Do a fluid and filter change and let us know how you made out.

[911 dreamer]

Just found another receipt - Esso gearbox oil x 6, 14/2/2013 at 87500 miles, it's done 92500 now so it's not done much since. Anything else I can check? I mentioned it to my independent when I saw him for a coffee recently and he said it's probably the gearbox 'learning' my driving style. He is the expert but it doesn't seem to be a very fast learner!!

[911 dreamer]

The fluctuation seems much more apparent when the engine is cold/warming up - it doesn't seem to happen when it's hot..

[911 dreamer]

Also, this might sound stupid but...my house has a gravel drive, on a bit of a slope and when I reverse off the drive (no clutch control in auto!) with my foot on the brake, weight is transferred to the back of the car and one front wheel becomes light and therefore drags/skids across the drive. Probably looks like I can't drive it to onlookers! So to avoid this, once I reversed down the drive and instead of using the foot brake, I used the handbrake as this only brakes the rear wheels - the result, no skidding but it was immediately after this that the problem with the fluctuating revs started.

 

Not sure if this means much but thought I mention it.

 

Many thanks!

[ac74394]

Could vacuum leak of some sort contribute to the hunting RPM problem?  Are all your hoses / engine plastics in good shape?

[911 dreamer]

I have now had the gearbox oil changed, the maf cleaned and the throttle body cleaned, but the fluctuation remains. I've even had an indie look at it but he found nothing, or it didn't show a fault so he gave up. What's the best way to check for a vacuum leak?

[Tall Paul]

Hi did you ever get this issue resolved - I’m getting similar symptoms on my 2000 C4 tiptronic...gearbox serviced and MAF cleaned but again fluctuates about +/-100rpm around the 12-1300rpm region.....fine when idling but only when driving.

Edited August 5, 2018 by Tall Paul

[wizard]

Just a stab in the dark but, 1300 rpm +/- is the point at which Variocam kicks in. If you have a Durametric, that should tell you whether Variocam activation is in any way related to your problem.

[Tall Paul]

Cheers - I’ll give that a look