16v - very erratic idle

[Gambit]

my 91 16v has started going a bit haywire the past month, once its warmed up to bout 90C on the oil temp

the symptoms:-

when coasting to a stop, or coming of the gas, the rev counter will start bouncing (and i mean bouncing) between say 2k & 4k and it start spluttering misfiring etc, and occasionally the oil light comes on

it will eventually clear itself if allowed sit (still running) for a few momemnt

im totally stumped by what this could be

its not the ISV, it dont work anyhow and has been disconnected also

i've cleaned all the earths up, and also cleaned the contracts on ignition unit

also, points etc all cleaned

and it still happens!

anybody any idea at all? it gets a bit embarrasing when it happens!!

Cheers,
Craig

[Miacant]

I experience the same problems with my '89' 8V except the oil light signal. I have been only using the car for 3 weeks now.
I'm new to GTI so I'm trying to get help. Info on this forum points to ISV as the problem and a mechanic I met by chance confirmed source of the problem as worn out ISV. He advised that I replaced ISV and problem will be resolved. Quote is ?40 for a used part (ISV) or new one....?140 from VW, plus ?25 an hr on labour. Hope to get some money soon to sort it out. It drives me mad most of the time. Well, labour of love!
 
For now I wait a few minutes for car to warm up before driving off. It really can be dangerous when revs counter goes up and down whilst driving.

[Gambit]

you can just disconnect your ISV to test it, the car technically does not need it to run

the idea of the ISV is that when the engine is under at idle, i.e. you have the rear window heater on, the blowers on, headlights lights on etc, then the ISV will counteract the drop in idle speed by increasing it a little

alternativily put your hand on it when the car is idling, if you can feel it vibrating/buzzing then its working

if its working then take it off and clean it out, either with petrol, or carb cleaner - they are easy to take off, two hoses & a switch and thats it - save you ?25

[roon]

Okay I feel stupid   I had that problem with my last 16v and never found out what it was. If I had some aircon or heater etc on I would often stall when I hit the clutch when stopping. It wasn't eratic. But the ISV clearly wasn't compensating then. What does ISV stand for anyway?

[Gambit]

idle stabilisation valve

[mk1]

With the engine running, do a "wiggle test " on all the wiring, also check the condition of all the vacuum pipes and the pleated rubber hose from the air meter to the throttle body for splts.
Steve.

[golfvr6]

The engine will hunt without the ISV connected, ie. it will not settle very well at idle.