Astra needing a cylinder head decoke?

When the dealer said a decoke they would have intended to remove the cylinder head and have a look inside, scrape the coke off, pop the valves out have a look , check the valve guides , check the cylinder bores for wear signs of seizing etc not just whack redex down the intake!

trouble with redex is if you get rid of coke from a clapped engine the oil consumption rockets.

It sounds to me like valve trouble, an exhaust valve not seating properly probably, so to fix it take the head off and have a look.

I've never heard of a modern engine needing decoking, that's a thing of the past. More likely the timing needs ajustment. Continuous local runnig can cause problems, give it a good long run so it can get up to a high temperature, that should help and it will get the water out of the oil.

It does sound like a weak cylinder but putting injector clean in the air take will do no good you need to put in the fuel system the only diy way is to put in the fuel tank All other adjust are done electronically but you could try a additive in the oil to restore compressions all car diy sell it

what you need is a correct diagnosis, The best way is to have a cylinder leakage test done, you will have to use a garage to do this, this if done correctly will pinpoint any sticking valves or burnt valves , head gasket leaks or just plain engine/cylinder bore wear,

Also a good engine tune company will have the equipment to check electrical side of it could be a plug. Your vauhall garage should have been able to do this (or do modern technicians lack these skills)

Unless you're using crap fuels, have leaky valve guide seals or lug the engine like hell under load, I doubt that there are enough coke deposits inside to worry about. If this is really bothering you, try an Italian tune-up every few weeks (drive up to redline a little bit).

have u tried giving a good hammering down the motor way in 3rd gear for a couple of miles.The astra suffer from sticky valves

You have done a lot of DIY. Now take it and get it tuned before you throw any more money away.

Try :

cavweb-forums.co.uk

vauxhallownersnetwork.co.uk

vauxhallforum.co.uk

I hope this helps.