Help needed from Idle Experts!

[IanK]

Guys,

odd issue with my S2.

It starts fine, runs fine for maybe 20 mins, then when I stop at lights etc the idle varies between 900 and 400 RPM & sometimes stalls when I'm braking to a halt etc.
I can keep it running smoothly at say 1100rpm with a touch of throttle.
Restarts instantly when I turn the starter. Whilst its doing this it also seems a little hesitant to accelerate at higher revs - not much though.

After a few mins, problem goes away and the car behaves perfectly.
Issue sometimes reappears for a few mins later in the journey - Eg on a 150 mile journey on Saturday I noticed it only at 20 mins and when I pulled into the driveway at the end.

This started (maybe coincidentally) when the AFM was changed a few weeks back.
I have had the AFM off and looked t the track/contacts etc, all seem good and checked that none of the vac lines are loose. I've also had the idle control valve off and checked that works as its supposed to - it does.

I'm thinking its temperature related as it seems to start just after the temp gauge gets up to its standard position - but then the AFM was a coincidence?
Its a niggle now, but as I'm heading off to France in it in a few weeks I want to make sure its not the beginning of a more problematic fault.

So, any ideas please?

Thanks

Ian

 

[GlennS]

I would suspect the throttle position sensor. I had similar temperature-related tantrums with the one on my 2.7l. It also lives in close proximity to your AFM so perhaps didn't like being disturbed.

 

[edh]

Check the plugs - is it running rich? (I'm thinking DME temp sensor could be failing)

 

[IanK]

Thanks Guys,

a quick look online suggests a DME temp sensor is only circa £20 so worth swapping anyway.

The TPS options seem to range from £40 to £120 - any ideas if brands such as "MEAT & DORIA" are good enough?

https://www.buycarparts.co.uk/porsche/944-convertible/2989/10806/throttle-sensor

Thanks

Ian

 

[Waylander]

its a bosch part, get the bosch number off the side and search for that,

 

[IanK]

DME Temp sensor on its way -Ill try that first as its cheaper.

Price from OPC was £40 + VAT, but only £18 off Amazon for a genuine Bosch one.

I've seen the genuine Bosch TPS available for around £76 so that will be next if the Temp sensor doesn't solve it.

Ian

 

[IanK]

OK, so the Temp sensor hasn't cured it, and I've now noticed a fairly consistent but slight hesitation when coming off idle when driving the car.

So Im thinking the TPS is going bad.

This looks easily accessible on the car but Clarke says the throttle body needs to come off.

Anyone done this?

Ian

 

[TTM]

The TPS will come off the throttle body after removing the two small screws. Replacing it should take 2 min if the screws are not rusty, maybe 5 if they are.

 

[IanK]

Thanks TTM - 2 mins it was.

For future ref, the Bosch part No is 0280120308 - paid £68 for a new one on ebay.

Seems to have cured the hesitation - but idle still not right!

Ian

 

[IanK]

Well,

this has finally been cured - by changing the clutch!.

Not really - when doing the clutch we changed the O2 and crank speed sensors (the one on the bell housing) so it was replacing one or both of these that solved it. Runs, starts and idles perfectly now []

Thanks

Ian

 

[Indi9xx]

If crank sensors and o2 sensors were replaced and it fixed the problem, then it would have been the crank sensor.

the oxygen or lambda sensor is ignored by the DME when the car is at full throttle, closed throttle, engine cool or rpm bellow around 2000 rpm.

 

[Indi9xx]

Good to know it is fixed though, and with a new o2 sensor you will probably enjoy better fuel economy now on cruising conditions.

 

[IanK]

Yes - my thoughts exactly - and yes, as a bonus its also drinking less fuel.

Ian