High idle issue

[DCmk3]

Now I've replaced the cambelt and tensioner, the crank and cam are lined up, set the timing with a timing light.
I checked all the vacuum lines for leaks/breaks and they're all fine, but I still have an issue with the car idling at 1400 RPM when I put the clutch in, the revs only drop down to 1000 RPM once the speedo reaches 0.

I disconnected the speedo cable from the gearbox and each time I put the clutch in the revs drop to 1000 RPM even while moving..
So is this down to a speedo drive issue or something else? Since when it's disconnected the revs drop normally, but when it's connected the revs hang at 1400 RPM until the car comes to a complete stop.

Anyone have any ideas?

[Christo77]

In your first paragraph with what you say..it's not easy to understand what is effecting what without a bit of punctuation.. apologies for that.
But anyways.. the idle valve (ISV) i believe only takes over the idling once the vehicle has come to a stop, ie stationery no wheels turning, it's all in the electronics/ecu.
Disconnecting the speedo cable i guess isn't really helping, only perhaps pointing towards an obvious idle problem, possibly ecu related.
Without going out to check i can't remember if the idle valve is affected by clutch in/out at standstill but if so, again it's in the electronics engine management i'm sure.

Kinda assuming you've done the ole ecu and fuel relays, among the other usual tricks and jobs.

[DCmk3]

I suppose I could have made it a little more understandable, I was in a rush to type it before heading out.
The car doesn't have an ISV of sorts as it's a 1.8i 8valve.
I've set the timing already and that's perfect, I set the throttle body with Vag-Com and all, there are no error codes either.
I just can't figure out why the RPMs stick so high when the clutch is in, then only go down once you stop completely.

I replaced the fuel filter two weeks back, checked the fuses and relays for the fuel pump and so on, they are alright.

[Christo77]

No worries ole chap..
Not having the idle valve then it might be a simpler problem,
I'm guessing a bit i know but if the clutch in/out is affecting idling then is it a clutch issue?  what is the engine doing with clutch depressed in nuetral at standstill... and also clutch depressed in gear at standstill.

[DCmk3]

It's an odd issue, even if I have it in neutral with the clutch out and if I push the car down the road the revs increase to 1400 as the speedo needle moves above 0. And as soon as the car stops (Speedo reads 0) then the revs drop to 1000RPM..

I just don't understand why it does that, my friend had a Mk3 with the same engine yet his never had this issue.

[Christo77]

It kind of suggests an engine management thing.. the wheels turn and the idle speed is being intervened in the same fashion as if there's an ISV in the system, although yours is behaving in more drastic way.

If it was me i'd have to go back to basics, check through all the known problem areas with these cars, even look at the earthing points.

[DCmk3]

I've read up a little, could the MAP Sensor be at fault perhaps?

[Christo77]

It could.. but i'd be guessing at it only, the same as i might be thinking is the MAF sensor a culprit in the system..
It's one of those situations.. if it was me anyway that i'd first replace any associated items that aren't too expensive, like relays.. good things to do with an older vehicle and at the same time tick them off the list of possible fault areas.
Sounds like your getting all up to scratch with it so i don't know really..

Another thing i would do is look at the plugs, sounds like a dumb shot but i'd want to get an impression of the fuelling/engine health.

[DCmk3]

Here's how my plugs are all burning;



Here's a little piece I got off a site:

Fouled Spark Plugs
Because a faulty MAP sensor can cause the engine to produce a rich fuel mixture, you may also notice the engine's spark plugs are fouled or coated with a white powdery substance. You can try to clean the spark plugs or install new ones, but the problem will not be eliminated until you address the faulty MAP sensor, which is reading the air and fuel mixture incorrectly.



Read more: Symptoms of a Faulty Map Sensor | eHow.com http://www.ehow.com/list_7468452_symptoms-faulty-map-sensor.html#ixzz2AbO3H8Ek

The car doesn't have a MAF either, so that can't be the case though..
I'll try price a new MAP Sensor, hopefully it's not too much and i'll go from there.

[Christo77]

The core part is very white isn't it.. might suggest a weak mixture if anything.. but again that can be caused by out of wack ignition timing also i think..
I guess if the Map sensor is cheap enough i'd replace it anyway.. as a means to piece of mind and eliminating it as a problem at least.