MK2 16v GTi will not hold it's idle when HOT

[ryanmc1302]

I have a '90 KR 16V which I bought a few months ago. It had idle issues when I bought it which a good clean out and new ISV sorted.
However, if I've been sat in traffic for a while the revs start to drop low when releasing the throttle and eventually it loses ability to idle altogether.

I have taken it to VW who set the timing, co mixture etc and eventually said they couldn't diagnose it.  Can anyone help? I've read about faulty temp sensors and hall senders being a possbile cause?

Any advice appreciated

[clipperjay]

search search search top tip search for ISV been covered many times 

[bodga]

clean up or replace the 3 temp sensors on the R/H side of the head. 1 is for the temp gauge and the other 2 feeds info into the ISV controller behind the ash tray in the centre console.

[ryanmc1302]

Just to add.. I've replaced the dizzy cap and arm, had the co checked as well as the timing set, cleaned and checked the vac pipes for leaks and cleaned the throttle body. There are no obvious breaks in the temp sensor wires although the MFA oil temp displays ---- even when warm. Does this control any other components and be a cause of the problem?

It idles and drives smooth until sat running for too long (40 mins ish). The temp on the dash never exceeds half way and isn't erratic.

I've arranged for the ECU and ignition module be swapped out for a mates spare and will post results. Any advice would be greatly received, this is driving me mental! 

[ryanmc1302]

clean up or replace the 3 temp sensors on the R/H side of the head. 1 is for the temp gauge and the other 2 feeds info into the ISV controller behind the ash tray in the centre console.

Thanks for this, i'll give it a try!

[bodga]

MFA oil temp sensor is back of the head R/H side, wire was broken on mine when i first had it, fitted a new spade connector job done!

[ryanmc1302]

I noticed a threaded hole next to the one of the 3 black temp sensors behind the dizzy.. worrying. Will this just be a missing fixing or is it a missing switch or sensor? I tried taking a quick photo but it was crap, hid the actual hole behind the sensor!  :embarassed:

[bodga]

See if you can get a picture up on here.

 here is a link to when i had a prob with these sensors that may help you


http://www.golfgtiforum.co.uk/index.php?topic=160322.0

the three sensors on the side of the head are all the same so swap them around to see if it improves

[ryanmc1302]

Update...
I swapped the sensors around which produced no real changes.

I then scraped and cleaned the sensor spades and connections, replaced the Ignition Module on the ECU and gave the over-run valve a good clean out. It's early doors yet but after a trip through the city centre this morning it was tonnes better! It cold started first time and idled at around 1K (give or take) consistently all the way to work, even when right up to temp where it previously deteriorated 

Im not sure which action produced the benefits, let's just hoped this post isn't premature..

Thanks everyone for your guidence and tips.