Wonder if anyone has some experience with the problem I'm having and provide the best place to look for faults that may be causing this.

Have a 2003 Seat Leon S 1.6 16v petrol, which won't regularly won't start. Seems worse on wet/damp days. Put in the key and a horrible whining starts coming from the engine. Turn the key to turn the engine and it just goes but doesn't fire up. When it does fire, it normally cuts straight back out a few times, then the engine starts and idles around 2-300 revs then cuts out. Finally, if it starts, it will again idle at 2-300 and the accelerator won't work, then finally shoots up to about 1k revs and goes.

I have given up on working the issue out, so passed it to my mechanic who is also bemused as to what is causing it. Sparks, coil and ht leads are all OK. New alternator and battery has been fitted. O2 sensor and ECU maybe faulty, but don't want to go down the route of sorting that out unless needed, as have already forked out over £400 trying to fix this.

Any advice on faults that may be causing this or anyone who has experienced similar issues and knows where to go, would be much appreciated.