Golf cold start problems...

Probably a vacuum leak round the inlet manifold. If you sit and blip the throttle midway every half second at idle, do the revs gradually build up?

Hmm. Haven't got the car here now to try, I'd have to ask him.

I know I could give it a very very light throttle and the revs would dip then build up to 3000+ slowly. But if I then tried to use that at all, even madly slipping the clutch, it died down to 3-400 instantly.

Wouldn't that affect the normal running too though? It goes well, and gets decent economy. It also recently passed the MOT emissions very easily.

If it's OK when warm then it could be a leak that's being plugged with metal expanding. I've seen it happen particularly with alloy heads and inlets.

Sounds like an air leak, the other thing to check is the iscv, they often need a squirt of carb cleaner.

That would do it. Knowing how he drives I'm sure it gets *very* warm.

He's a good driver technically (can handle it very well, place it exactly wher he wants it etc.) but I've been encouraging him to try the RoADAR or IAM to try and divert some of his efforts in a safer direction...

Wouldn't the ISCV only affect it *at idle*? Like I said, it idles well and only drops the revs when you apply throttle, which AIUI means the ISCV would be out of the circuit until you take your foot off again (when it runs smoothly again).

Air leaks sound the most likely bet so far. I guess that would have to be either the inlet manifold gasket or where the carb/throttle body fits onto it? (Not sure what engine it's got, don't even know if it's carb or injection.. '96 Golf is all I noticed!)

If it's working yes. If it isn't then it can drive you nuts.

It'll be somewhere downstream of the MAF sensor.

Most likely Digifant 1 or 2. I'd guess at TPS.