Hello,I have just replaced the head gasket on my 8v MPI. The head was very badly warped and I have machined 1.25mm to achieve the required flatness. I realised that the compression ratio would increase so I have measured it at 10.78:1. Now it is back together, it is erratic at idle when cold and does not respond to acccelerator depression without the revs dropping until the engine is warm. Does anyone know if this is due to the engine management system needing altering to cope with the new CR or does it have something to do with spark plug gaps? Please help.

1.25mm :eek: thats a huge amount... :eek:

That head cannot be skimmed by that amount. I wouldn't be surprised if the valves are almost in contact with the pistons.

Checked that and they are clear. Compression ratio is a little higher thats all. Checking usual suspects, split hoses etc. Going to change the plugs also maybe this will work.

1.25mm is a lot higher, not a little.

I took 20 thou off my race engine which equates to about 0.635mm.

That means you've effectively taken off 3 times the material i took off on my race engine! :thumbdwn:

Should really have had the valves re-seated back to take up the compression difference

Ran it today, seemed to go great when warm. Little juddery on take off, but this was the case before the gasket went, the problem is now more prevalent. I need to know if bad idling is a symptom of the higher compression ratio or if I have another simple problem with one of the air flow pipes or one of the sensors. I am sure that the increased compression ratio is not a problem as it does not pink and drives superb when warm. Just need to sort out the cold idle problem and I'm away. Can some one out there please help.

Just need to sort out the cold idle problem and I'm away. Can some one out there please help.

You could just move with it to a hot country? Seriously though, sounds like a big job so well done for taking that on. Wonder if it is worth trying to reset the ECU/disconnecting the battery and then getting the ECU to "re-learn" the engine map?

In the old days we just used to bung an extra gasket in :eek:

In the old days we just used to bung an extra gasket in :eek:

One of the most impressive bits of engineering I have seen was on early fiats. They didn't even have a head gasket, just precisely engineered blocks and heads.

Thanks for the advice guys. Took it to the VAG specialist today, found that number 3 cylinder is low on compression, the other 3 are showing 190psi while the number 3 is only at 20psi. Explains a lot I suppose. No recorded faults apart from engine missfire which is also expected. Going to have to take the head off again and check out what is the cause. So far, cost for head gasket replacement is about £50. Suppose if I can do it for a ton, then I am doing well, specially as the cheapest quote from a garage was £350. Keep you posted.