Very poor idle.

Posted: Wed Jun 27, 2012 7:00 am

When I was last home in March my 20v 90q developed poor idling. In fact by the time I left it wouldn't idle at all. It started with poor starting when hot with sometimes cutting out at junctions. It deteriated quickly to a point where it now cuts out when the throttle is closed when stationary and very difficult to start when hot. Methinks it may be a timing issue but I could, and more than likely will be, wrong. I'm home again on the 20th July for three weeks and would like to get this issue sorted quickly as I there are track days to be done.

Cheers all.

Steve

Posted: Wed Jun 27, 2012 12:55 pm

With mine, I found idle issues had one of two causes:

1. Idle bypass screw or idle control solenoid cruddy.
2. Air leak.

Symptoms were the same hot or cold: poor idle, roughness at low engine speeds, but everything hunky dory on wide open throttle.

Poor hot starting (but OK idle) was due to leaky injectors.

Given that the ignition timing is fully electronic & non-adjustable, it would not be the first thing I checked.

Ian.

UltraUser Joined: Mar 18, 2005 Posts: 1570 Location: Gwent

It won't hurt to clean the idle screw, but I think, that this would not cause the hot starting to deteriorate, so the vac leak is more likely, look for splits on the 'michelin man hose' esp underneath. The crankcase breather hose is another likely culprit, if it has not been done?
Something like a bad ECU temp sender (2 pin white, on back face of head) or O2 sensor could be at fault. Possibly a good idea to clean the MAF sensor elements too? oil fumes from breather can contaminate them. Also check the vac feed to the fuel pressure reg is intact at both ends

Posted: Wed Jun 27, 2012 9:08 pm

check all the earth's, over and above scotty33's recommendations- I think there's one to the inlet manifold- had a similar issue years back. Bolt into the manifold connecting the earth point was missing....

if a timing issue, I would not expect it to start at all (and if that's the case, first thing I would check is the dizzy gear, unless is not plastic)

Posted: Mon Jul 02, 2012 3:45 pm

Thanks guys. Interesting points you have made. I'll take a look as per your recommendations and see what happens. Watch this space.

Audi Nut Joined: Aug 22, 2011 Posts: 62

I had poor idling on my coupe, changed the lamba sensor which helped Wink

Posted: Fri Jul 06, 2012 2:59 pm

We have a result. Got home last Tuesday and checked all the things you guys mentioned. Ripped the thing apart. No air leaks cleaned the ISV and everything else. I noticed on closing the throttle the engine speed would slow down very slowly. So I checked the idle switch on the throttle body. This was clicking fine but I noticed that the potentiometer was looking a bit worse for wear. Because it sits close to the down pipe from the turbo it got a bit roasted shall we say even with some heat shield rapped around it. I did not know at the time if it was either the idle switch or the potentiometer at fault so I managed to get hold on a replacement throttle body from VW Audi breakers in Melksham. Fitted it and jobs a good 'un. Just need to tweek the idle to make it perfect. I'm also going to build a better heat shield to protect it as well.