Warm starting issues

[iDub]

Hi guys. I've got a weird problem with my avant. Sometimes, when warm, it takes ages to start. I'm talking 10 secs of cranking! Even then, sometimes it either stalls when I let off the key or idles really low (500 rpm) before gradually picking up. At the same time I can often hear a gurgling noise from the fuel tank! If it stalls and needs restarting, it'll then behave perfectly.

When cold it always starts within a second or so.

Any ideas?

[UrS4boy]

Any ideas?

A few. Not starting means either no fuel or no spark or both. Most of the time, it is fuel, especially with these symptoms. The main suspects are the G40 cam position sensor (I presume your engine is an ABY if you have an Avant). These can get flaky and act up before they finally die. When there are problems, it should throw a CEL code but they don't always. Next time you have trouble starting when warm, pour some cold water down the back of the cam belt cover. This helps to cool the CPS and the car will likely start right up. Here is some CPS info that might help:

http://forums.audiworld.com/showthread.php?p=18849794

and CPS replacement (note this one is for an AAN but an ABY will be very similar):

http://picasaweb.google.com/persing/CamPositionSensorReplacement#

Another potential problem is the Mass Air Flow (MAF) sensor. Sometimes the wire gets too dirty (e.g. from excess K&N filter oil on a re-oil job) and needs to be cleaned (isopropyl alcohol seems to work). Other times, the MAF connector is the problem, either because of dirty corroded connectors or pins that aren't pushed completely together. Here is some MAF info:

http://forums.audiworld.com/showthread.php?p=18863095

And then there is the G62 coolant temp sender on the back of the head. If it dies, then the ECU will think the engine is cold and provide too much fuel on start up. Here is some G62 info:

http://forums.audiworld.com/showthread.php?p=18871694

Good luck. Let us know what the answer is.

[iDub]

Cheers for the reply mate. The previous owner replaced all the sensors but I'm not sure about the MAF. I'll give the ol' IPA dunking and see what happens. The fact that it starts perfectly 2nd time around really puzzles me though!

Another issue is that unless the car is up to temp, the revs dive quickly (down to 500 rpm or so) when I lift off, and then rise again to idle. When warm it's all good.

Could these problems be related?

[Jamo]

Sounds like ISV to me, check that the fuse hasn't blown to the ISV valve and clean it out with WD40 as it gets full of gunk from the PCV system.

[iDub]

Good call. I'll try cleaning the isv and see what happens. It worked wonders on my old 16v golf!