Rough running GSi - any ideas?!

Quick question as I've been having a think tonight - in the last few weeks my GSi has been having a problem when warm between 1000 and 2000 revs, it sounds like the timing is slightly out and it's missing - but I don't think it is (but it might be), it just seems to really struggle when initially put under load but after that it's fine until the next time you get to a junction / roundabout etc.
I'm hopefully going to remove and clean the EGR valve, check the inlet air pipes (cheers Ben for the idea) and get a compression test done tomorrow (if I have time before leaving for PV) to rule out a possible head gasket failure but as the gasket was only changed within the last two years (along with new piston rings) and there's no trace of oil/water mix in the rocker box or headertank and the fact that it doesn't do it all the time I'm kind of doubtful that's the problem, I've had a look at the condition of the plugs and they don't indicate a rich or lean mixture so that looks spot on, dizzy cap and rotor arm are both fairly new (might of started when I changed them or it might just be me imagining it!), I've checked the timing and it's fine, I've replaced the TPS twice (cheers Bruce and Nick for sending me their old ones) and it still does it - any ideas?

Now, baring in mind that it only does it when it's warmed up I'm thinking what would happen if I disconnected the power to the auxilery air valve? As far as I can work out this is what tells the ecu when the engine is warm or not and adjusts accordingly and isn't really something known for going wrong (the aux air valve closes more the warmer it gets until pratically fully shut off) so by unplugging this it *might* fool the ECU into thinking that it's not warm and will do whatever it's doing to make it run sweet? Or will it just fcuk the mixture up, lean it right up and burn a whole in a piston?! :lol:

Thinking about things like this at gone midnight on a Friday night / Saturday morning after a few beers isn't advised!
:?

No-one?
:?

Quote:

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Originally Posted by Jules

so by unplugging this it *might* fool the ECU into thinking that it's not warm and will do whatever it's doing to make it run sweet? Or will it just fcuk the mixture up, lean it right up and burn a whole in a piston?! :lol:

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more than likely option 2

have you tried changing the plugs? or did you just check them? i had a problem like this on mine it turned out to be a hairline crack in a plug took me ages to find the bugger. also get a new dizzy cap and rotor arm, for what they cost new it's now worth going round in circles over.

hope this helps

Cheers Benji - It's going for a compression test on Monday at my mates garage to see if it's the head or head gasket - I'll be pissed off if it is!
Hopefully it'll be something daft like the plugs but they were replaced when I changed the dizzy cap and rotor arm about 8 months ago (brand new GM items).
I guess I'll have to wait until Monday to learn more........
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Edit: oh and by unplugging the aux air valve it made no difference but also didn't knacker any pistons neither! lol

Faulty coolant temp sensor?

Hope, I changed that not long ago............
It's the head or the head gasket (or the piston rings etc etc) - it has instant compression in the headertank so the compression is leaking into there somewhere, luckily I have a old head knocking about which is getting skimmed today and put on tomorrow along with a new head gasket - I just hope that it's not piston rings as 1) it means more faffing about, and 2) because they were done not too long ago..........

I bet I know which one it's going to be though.... :?