Porsche Enthusiasts Club Forum

When I start my engine the RPM is at 1200 and soon drops to about 600, which it's always done. However the last couple of times I've been out in the car it has done this, then the tickover has gone up to 1200 rpm again and sounded a bit uneven/rough. After a short time it goes OK.
I'm wondering if it's the cold weather, or something else.

Not sure, but my 911 was similar the other day. It's normally garaged but was out/about for a couple of days. I noticed a bit of a rough tickover which I put down to dampness. It soon sorted itself out though.

Which model year?

Hi

WHEN were the plugs, dizzy caps and rotor arms last CHANGED ??

Not looked at or checked but actually CHANGED ???

All the best Brett

The rough/high tickover clears after a few minutes (so when I start the engine it's OK, then when I stop at the bottom of our hill it's gone rough, but by the time I get to the village about 4 miles away it's gone OK) This is going out in the car after it's not moved for 2 weeks by the way.
Could be condensation? As it's cold weather, and my garage is unheated. Distributor caps I've had off and they look perfect. Plugs and HT leads I've not looked at, so have no idea. I'll order a set of spark plugs. It's a 1989 S4.

Number of possibilities for idle surge/rough running Lightning.

Try simplest fix first. Believe it or not some LH Jetronic idle problems can be fixed by the IT dept solution of turning it off and on again, or rather disconnecting the ground strap. After reconnecting start engine and let it idle for 5 minutes before driving off.

Your car may also simply need the idle adaptation routine running. Again this will fix many idle problems as effectively the injection system is set to correct idle speed allowing for precise condtion of its components.

To run the adaptation you need JDS Spanner or Bosch Hammer. Any OPC or Porsche independent should have the latter, as idle adaptation is required by the major service routine.

After trying these simple approaches, you can start thinking about things like a sticky idle valve stabiliser (quick fix involves a shot of WD40), or maybe a faulty throttle position switch not registering the idle position (when you move the throttle quadrant at side of intake just slightly, do you hear distinct click - full test is to check at the LH plug pins as you operate throttle).

With JDS Spanner/Bosch Hammer you can also run the whole gamut of LH/EZK tests automatically which will identify any problem.

one of my cars did this the other day, absolutely perfect for months, it thaws, rains, and then runs like crap.

day after fine, and has been fine for weeks since!

Mine was odd after the snow too. One of those things I guess where they are getting on and everything not quite as new and in tolerance.