Hot idle issues - K jet expert needed

Hi guys,

I am having issues with my hot idle.

Working through the system logically,

When the car is cold ie this morning where it was very cold, the car starts on the button and idles at 1000 rpm, nice and smooth, pers like a kitten

As the water temp needle moves into the white segment of the range, the idle drops to 800rpm and still smooth.

This tells me that the cold start system and the Aux Air valve is working as intended. Correct? The AAS has got warm, closing off the air bypass reducing the air going into the engine and therefore lowering the idle.

has the car continues to heat up, needle is now half way (straight down) the idle gradually drops as engine temp increases and eventually stops around 200rpm. At this stage, the motor is no longer purring, but throbbing and the whole dash is vibrating.

Having read up on the WUR, as the engine heats up, it reduces fuel pressure. Why would this be causing the idle to drop? If I apply gentle throttle to bring the rpm back up to 800rpm, the motor is smooth and ticking again.

While driving, there are no issues. Smooth and quick.

What needs adjustment to correct this? raising the idle speed will effect the cold idle too I take it, which is currently correct.

Any ideas?

to start with give the system a good going over to ensure no air leaks, particularly in the folds of the inlet boots. the idle screw oring may well be worn now too so worth changing that also.

see tyhis guide as well, ignore the 16v specific bits just look at the basic kjet sections. for the ignition timing on a 1.8 8v this is done at idle with vac line to dizzy disconnected and plugged:
http://www.vwgolfmk2.co.uk/forum/viewtopic.php?f=37&t=25972

thanks will have a look.

If it was an air leak issue, would its effect change with engine heat?

maybe if say base idle set wrong and vac leak together coudl throw out the aac bypass warmup curve?

generally you would expect idle to be higher with vac leak but its best to make sure everything setup and vacuum wise is tip top before you start changing bits and pieces

Try increasing the idle speed once the car is warm to around 950rpm, the idle screw/bolt is at the back of the throttle body 7mm spanner needed. The idle screw does have a habbit of unscrewing it self and has a rubber O ring which can perish which does not help with the idle you can remove the idle screw and see if you need a new rubber o-ring, it's only small.

 

Get your co% checked. Could be running weak when warmed up or try turning the co screw clockwise half a turn to see if it picks the revs up any.
I took mine out at the weekend and had a similar symptom and this cured it. I put it down to the cold denser air of winter.

Cheers for the tip. I will give it a try at the weekend

Hi Amit,
Did you have any joy to this?
Your original post descibes pretty much exactly the same problem I now have.
Cheers