Low Idle Issue

[TomSan]

Hello fellow GTI fans. I've got a MK2 8V Digifant, 1990 reg with a 92k on the clock. It's been kept in good condition and passes it's MOT every year - but I have a problem I cant solve. Any help with this would be appreciated.

When starting from cold, the idle will struggle to get above 800rpm. During the winter, it was much worse and the idle would sit around 400rpm. Cut out's would ensue and so I barely drove it all winter (not good). During the warmer months, after the engine has got nice and hot, it tends to sit comfortably around 850rpm.

I have purchased a new blue temperature sensor and that made no difference. Pulling the sensor out while idling makes it sound like a tractor, so I will assume that it is doing it's job. Last year it was in the garage and they said it was probably the cold start device, but showed no interest in actually fixing it.

What else I know is that they said the CO adjuster is not working, so they had to open the unit up and manually adjust it (not so happy about that either). It did just pass the MOT with very good CO readings (but I did enhance that by having the foam filter out of the air box).

OK, I think that's about it. Hopefully someone can make sense of my ramblings and will use their mechanical super powers to help.

Thanks again

Tom

[Sgt_Lemon]

What happens when you unplug the idle control unit? When mine went it could barely idle without stalling till warm. This might be your culprit.

[TomSan]

The idle was fractionally worse. Plugging the electrical cable back in made next to no difference.

Should I clean it out? Test the resistance (not sure how to)? I've heard hitting it with a rubber hammer can work :-)

Am I right in thinking this is a reasonable price to get anew one if I have to? http://www.eurocarparts.com/ecp/c/Volkswagen_Golf_1.8_1990/p/car-parts/engine-parts/fuel-and-engine-management/car-engine-management-parts/?436440160&1&fb3b7b1ab8a92997209b443e1cfd7da4eea1529a&000502

Thanks for the response Sgt!

[oakgreener]

Does it buzz with ignition on? If so, clean it out with carb cleaner before you buy another.

[TomSan]

Indeed it does buzz when the engine is on, a lot louder than I ever remember it doing so. I've never taken one apart before so this should be fun - I'll update the thread when done.

Appreciate the responses!

[Sgt_Lemon]

You could try cleaning it first, take it off and swish it out with some carb cleaner.

[Santiago]

With the car idling, do the revs dip/drop if you put some heavy electrical loads on? e.g full-beam headlights plus rear screen demister plus putting an electric window up (if you have these).

The idle should stay steady as a rock if the ISV is working. If you do recognise this load-dependent idle symptom, don't jump to the conclusion that the ISV itself is the problem, it more than likely isn't working because the ECU isn't getting the message that it should be in idling mode, so isn't telling it to work. It can't hurt to give yours a clean, but I doubt it's at fault unless it's really gunged up. I think you'll soon discover that it can't be taken apart in any reversible way.

[borax]

I have the same issue i am looking into. Def try cleaning the idle control first as they are very expensive. I have read somewhere that this could be an issue with the throttle control switch on the throttle body, but not sure what/where this is, im still investigating.

[TomSan]

With the car idling, do the revs dip/drop if you put some heavy electrical loads on? e.g full-beam headlights plus rear screen demister plus putting an electric window up (if you have these).

The idle should stay steady as a rock if the ISV is working. If you do recognise this load-dependent idle symptom, don't jump to the conclusion that the ISV itself is the problem, it more than likely isn't working because the ECU isn't getting the message that it should be in idling mode, so isn't telling it to work. It can't hurt to give yours a clean, but I doubt it's at fault unless it's really gunged up. I think you'll soon discover that it can't be taken apart in any reversible way.

Dang, full beams on really highlights that it isn't doing its job. I've taken the isv off and it looks quite clean from what I can tell from the 2 open areas. I'll spray it full of carb cleaners next.

I have read on the forums that because the isv is buzzing when idle, it is doing its job? So something seems amiss here as the thing buzzes like a... Well a buzzing thing. It will be interesting to see what borax, to see if there is other things I can check.

[Sgt_Lemon]

Try pulling your throttle switch, that may have broken wires so the car doesn't know it's idling. The wires sit just above the manifold so are prone to cracking and throw up symptoms like this.