Tick-over speeds

[sawood12]

Well 3 weeks into the trusty old Porker being the workhorse of the household while the wife waits for her new car to be delivered in mid Sept and it's been fantastic and i've got to know and enjoy it so much better. However the only thing that has manifested itself over the past week or so is the tickover speed changing. Recently I had a nearly new AFM fitted but in the last week i've noticed that when the engine is cold and you rev the car to say 2000 rpm it will stay there and not fall back down to normal tickover rpm. If you drag the clutch a little to lower the tickover rpm it will stay there.

On the otherhand when the engine is warm it will tickover happily at just over 1000rpm (where previously it ticked over at the usual 850 ish rpm) but when you rev the engine it takes longer to return back to the 1000ish tick over.

Fuel consumption & performance appears to be normal and there is no smoke out of the exhaust and temps and pressures appear to be normal. It also drives normally it's only an issue at tickover.

I've been reading up about adjusting the idle speed but don't know if I should in case there is something wrong. Do these symptoms sound similar to anyone? I've checked the throttle cable isn't sticky or the throttle spring itself hasn't lost it's spring.

Cheers.

 

[sawood12]

Looks like it may have been caused by a deformed floor pan under the accelerator pedal due to using the jacking point that is not a real jacking point just behind the front drivers wheelarch. Actually I usually use the proper middle jacking point and only use axel stands on that point sharing the cars weight with the stand but due to the hot weather racently my jack must have been sinking into my tarmac drive therefore moving more and more weight onto the axel stand.

I'm still slightly suspicious though because I havn't jacked up the car since the problem has occured. I'll see how it goes over the next few days but for now it's purring like a kitten.

 

[Diver944]

I have a picture in my mind of you driving around with a lump hammer in hand waiting for the idle to rise again []

My Turbo has similar symptoms. Its with Jon Mitchell for a full rebuild at the moment and its on his list of things to check. He believes it could be a slight air leak through the TPS plug on the side of the throttle.

 

[sawood12]

I first suspected an air leak so went round the engine with liberal amounts of WD40 but engine appeared to be airtight - mind you i'm not sure how good or sensitive the WD40 method of air leak detection is. My local Porsche specialist rekoned it was the throttle thing and so adjusted the throttle stop. Like I said before i'm still a bit suspicious as i've not jacked up the car since the problem developed but in the absence of no other symptoms or problems i'll have to wait and see.

 

[Diver944]

The only sure fire way to check is by putting the intake under pressure. I borrowed the Arnworx pressure tester from Andrew at Promax. You remove the hardpipe from the turbocharger to the intercooler inlet, plug in the arnworx and pump it up. Spray fairy liquid on the throttle body and see the bubbles appear like magic []

The cause is a worn or shrunken O ring seal where the throttle shaft connects into the TPS. At idle or when lifting off, this leak sucks in air after the AFM so is unmetered and affects the idle.

Thats the theory anyway [&:] Unfortunately its outta my hands at the moment []