1991 mk2 16v KR calling a k-jet expert!!?

[H981CVV]

Right i've been having major hunting issues with my mk2 16v, i've tried everything on this forum to cure it but so far no good, so i thought  i would have another go tonight, and found that:-

From cold it idles perfectly for 30 secs to a min, then it hunts + - 750 r.p.m, until its warm (oil temp + 60)

tonight i found that if i disconnect the plug going to the micro switch on the throttle body, it will idle at 1000-1050 but steadily, why is this?

the micro switch is new, the i.s.v is clean and air there arent any air leaks in any pipes, the control unit behind the dash is new, i've checked all the temp senders on the side of the head under the dizzy, you name it i've checked it.

so can it be:-
fuel filter under car
lift pump
throttle body
e.c.u

please help
Ben

[Conker]

I dunno about being a k-jet expert, but I can suggest a few things... I went through a huge list of possibilities to finally fix my 16v hunting problem - Perseverance is the key! You'll find it eventually.

Anyway, the throttle switch tells the ISV to "turn on" and start controlling the idle, so here's my thoughts:

1) The ISV may be clean, but it might be knackered, so when it "turns on" it can't control the idle. Is there someone nearby that can give you a known working ISV?
2) I've said before "yes, yes, I've definitely checked that..." and it turned out I hadn't checked it well enough. Air leaks, temp sensors etc. etc. - Double check them.
3) I replaced my ISV controller behind the dash with one that was supposed to be working (an ebay special), but it wasn't. Are you sure you've fitted a good one?
4) Have you done the Haynes test on the idle switch, even though its new? "Using a ohmmeter, check that when the throttle is closed resistance is zero across terminals 1 and 2, and infinity between terminals 2 and 3, and vice versa when the throttle is open."
5) Check unplugging the over-run cutoff valve doesn't cure it (this one's a long shot!)


To be honest, when mine was hunting I hadn't quite hit the sweet spot in the CO2 setting vs the idle screw, (although if I was being 100% honest the main solution on mine was a rare one - it was actually an oil change that cured mine - the oil must have been contaminated and the fumes were affecting the idle via the crankcase breather  ).


If you want to see the long list I made at the time, see here:  http://www.golfgtiforum.co.uk/index.php?topic=71501.msg569972#msg569972

[maxp]

Im sure this vid will be of absolutely no help at all but might be worth 30 secs of your time on the off chance
 http://uk.youtube.com/watch?v=wpFX85Nv0xE

[rubjonny]

as above really, try another isv and check the idle & co!  there is a how2 on it

[H981CVV]

does anybody know which of the 3 senders wires under the dizzy work with the ISV and which one controls the temp gauge so i can just plug that one wire onto the sender and do some diagnostics. i would prefer to check that replace all the senders lol

[Conker]

does anybody know which of the 3 senders wires under the dizzy work with the ISV and which one controls the temp gauge so i can just plug that one wire onto the sender and do some diagnostics. i would prefer to check that replace all the senders lol

Yellow & Red = Dash temp gauge
Blue & White = ECU / Ignition Control Unit
Red & Green = ISV Controller


Apparently both the Blue/White and Red/Green senders will have an impact on your idle.


PS...  It takes a little while for the dash gauge to re-adjust when you plug it onto a different sensor (mine did anyway), so give it a second or two.

[H981CVV]

thanks alot thats ideal, also i've just been playing, i did the test on the micro switch where you rev it to 2000 rpm ish and click it, now my rev's didnt blip/drop at all does that mean the switch it broken? it is brand new from vw so ??

[rubjonny]

could be down to a bust idle control unit, or it isnt getting power.  does the isv buzz nicely when ign is on but engine off?
test the throttle switch electrically also, note the haynes procedure is wrong, you test it like this:
1 Pull the wiring connector from the throttle valve switch.
2 Using an ohmmeter, check that with the throttle closed there is zero resistance
between terminals 2 and 3 but a reading of infinity between terminals 1 and 2. With the throttle open, the readings should be reversed (see illustration).
3 To adjust the switch, insert a 0.10 mm feeler blade between the throttle lever and stop (see illustration), then loosen the screws and move the switch towards the lever until the contacts are heard to click. Tighten the screws on completion and remove the feeler blade.

[H981CVV]

thanks i'll try that later on and report back, also where abouts is the warm up regulator? i thort i might check it out as i havnt come across this component yet?!

[rubjonny]

thats the metal thing on the side of the engine block, with 2 fuel lines to it