idle goes up and down after a cold start

when the gti is cold it fires up straight away, but then the idle varies from 1000rpm to around 1300rpm and back. When I drive it 500 metres and press the clutch the idle is a nice even 1200ish.
A fitted a new auxilary air valve, so now I got rid off the cold 700rpm idle.
It has a new fuel pump,injectors, and fifth injector, and I cleaned out the metering head/warm up regulator filter and I have done the fuel delivery test on the injectors which was near perfect! What could could cause this problem??  During a constant speed, it still hesistates! Lowering the CO percentage to 0,7/0,8 has improved constant speed but not the idle which is a bit rough…..
Any help is much appreciated :wink:

yal

not sure to be honest but sounds like you've just solved my low idle problem  :wink: sounds like what yours used to be like so new aux. air valve is my next job :y:

could be a cracked pipe casuing a slight air leak maybe?  :dontknow:

you can test the resistence on the aux. valve, i can give you the values if you want! You can also test it bij starting the car with a cold engine and squeze the top hose from the aux. valve if the rpm does not lower its not working. I can hear the extra air going through the pipes, as its quite noisy!
It is a quite expensive part and was around 120 euro.

Good luck,
greets yal

Do the UK GTIs have O2 sensors?

Matthew

mmclaughlin said

Do the UK GTIs have O2 sensors?

Matthew

No Mk1 Golfs are all mechanical with no electrical feedback.  Only feedback I guess is the engine temp via the warm up regulator.

Cheers

Rich

does nobody know whats wrong with my car? I spent a little fortune on it so far, and still hesistates at constant speed and the cold idle is still going up and down… :dontknow:

greets yal

Yal,

Go through all the "When you buy an FI Car" tests and checks.

If you do not identify the issue there go through the electrics.  Is the dizzy advancing properly?  Coil breaking down? Bad wiring?

Check the condition of the air filter and for any obstructions to the air flow.

Will the engine run smoothly at 2000rpm when stationary? at 3000?

Can you adjust the mixture to get a sweet spot at idle?

Is the ignition timing correct and staying stable at idle?

Cheers

rich

thanks for your reply Crazyquiff,
where can I find the "when you buy an F1 car" test and checks???

My dizzy advances, and mechanism is not stuck
I did al the electrical tests the haynes manual suggested, and the coil was ok.
When I tested the hall sensor I got 11 volts, haynes did not state a max. value only a min value of 4 volts.
My air filter is clean.
When I do the prowler test I get nearly the same quantity fuel at all 4 injectors. My new 5th injector does not leak.
The engine hestistates when driving at a constant speed, and also when at idle and when stationary at eg 2000 or 3000 rpm.

I can get a smooth spot when turning the mixture on idle!!!only then the engine hesistates more when its driving and on acceleration!

When I make the mixture leaner to around 0,7% idle gets a bit worse but the car drives better(accelerates a bit slower, duh with less fuel thats normal I think)
Its got new Beru ignition leads and bosch W7DTC triple electrode sparkplugs. Compression is perfect, only 125 000km and a new cilinderhead fitted.
Thanks for the help so far

greets yal

yal,

You can find that here http://www.vwgolfmk1.org.uk/modules.php?name=Forums&file=viewtopic&t=2948

Your problem might be a "sticking" metering head - might be worth trying another one to see if the problem goes away - they are not that expensive used and may help narrow the search - i.e. if problem remains then deffo not the metering head.

Cheers

Rich

I would also check for wear in the dizzy shaft. Your timing may be wandering slightly causing the hesitation.

thanks for help, crazy and dub.
Did all the tests that crazyquiff gave me, and I only havent touched the accumulator but I will. It does maintain pressure fine, as it always starts fine cold and warm and after standing for weeks!!
I polished the plunger in my lab, (as Im a dental technician) and all the scratches are gone now! Shines lile new! Plunger moves freely.
I would be tempted to buy a second hand one, but its almost impossible to find second hand parts here in Spain as the mk1 was hardly sold here!
Thats why I buy mostly new parts…..

I found out, that when I lower the CO% to around 0,5% with crank vent off the car does NOT hesistate when driving at a constant speed, but the idle is a bit rougher then!

I now raised the CO% to 0,8% and the cars also stutters when I accelerate, when I accelarate straight away after that again its fine!

grr, annoying  

greets yal

just cleaned out the fuel accumulator, no water and not much gunk came out…
Fuel pump is new, and I checked the plunger moves freely in the fuel distributor. I then took the car for a spin, and hesistates with CO% on 0,8 the same with 1,0&1,2%

What I find strange, is when I go downhill and dont touch the accelerator the car still hesitates!! When I press the clutch its gone, so its def. something with the engine….

 :dontknow:    yal