ROVER 25 - Very Sluggish - fault codes read.

It appears now that it has always been a little sluggish since having the head gasget done, and I suspect is not good on MPG now. Could this be caused by incorrect ignition timing?

absolutely yes.

If the cam is mistimed it would be sluggish

The Intake air sensor won't help either.

I have seen that as a spurious code on quite a few vehicles, when there is nothing wrong at all with the IAT. I guess that people have tried disconnecting the first bit they can see (with it running) which generates a code that sticks.

As the fault has occurred after head gasket change the first thing is to check that the mechanical bits are correct, such as cam timing, running on all cylinders, those sort of things, if that is OK, Clear the codes, take it for a drive, read the codes (if any)

Ah, I was presuming it appeared immediatley after being cleared.

I usually find that most people (pro and amateur) try to read the codes straight away and rigidly go by that, I find that loads of spurious codes can come up even on cars that run well, clearing them, then driving it is the best bet I find (as does the only other bloke I trust to intelligently read codes)

Mrcheerful

I always like the VAG CAS sensor fault code, which ,means the engine's not running.

In message , Mrcheerful writes

Bloody hell, someone who knows what a scan tool is for. Quick, get him stuffed and mounted.

Only posted to second what you say, scan tools are only as good as the person who's wielding it, any muppet can change the bits the computer says are faulty but a proper tech will work out why the computer said it was bad.

As for the OP, if the o2 sensor is still showing bad after a good run, then I'd check for air leaks as well, especially as the head and all the induction stuff has been removed and refitted. I'd also be concerned that some sort of non o2 sensor friendly sealant was used.