Strange running problem!

[merlin's S4]

My S4's not been happy this week. It's not idling very well and the revs die causing it to stall when you first start it up. It won't rev properly if I try to keep the revs up with the throttle and it's extremely hesistant. It does settle down after a couple of minutes and it does drive but again is very hesistant and at anything above 0.4bar it feels as though the ecu is retarding the ignition so it doesn't pull like it should. Also noticed that the MIL (ecu) light which I have fitted in the dash intermittantly lights up when you're driving and then goes away again. This may happen several times on a short journey. I'm wondering if it's detecting knock? However there are NO fault codes stored. Been round Dan's (dpicariello) today (Thanks mate!!) and have swapped the coilpacks from his S2 and cleaned the ISV but it's not made any difference.

Please help!

[A80Avant]

as usual,check the MAF and also look at the vaccum pipes.Mine did this at the beggining when i first bought the rs2 and a vaccum hose off the IM had broken loose.

[s2driveruk]

was also thinking vac lines or lambda

[Dpicariello]

If you're not having much more luck this week with it then I'm back home Wednesday for the rest of the week. More than happy to take parts off mine to help identify the problem.

Plus you can have full use of the garage so doesn't matter what time you get round.

Run the car until there is virtually nothing left in the tank and then go and fill it up with fresh fuel. If that doesn't help then it at least eliminates the possibility that it might be dodgy fuel.

[Knight Rider S4]

Sounds like Lambda problem .........I would unplug the maf and take for a spin see if it helps

Take the plugs out and see if the problem is related to a cylinder i.e plug,injector,coil pack or fuel mixture being weak

[merlin's S4]

Thanks for the suggestions so far. Pretty sure it's not a vacuum hose and spark plugs look ok. Was wondering whether it could be dodgy fuel although I filled up with V-Power last so it's unlikely. Just ran the tank down and put some fresh fuel in with some Forte cleaner so that should prove or disprove that theory. Another thought was whether it could be a blocked Cat as I'm sure I can here rattling in the exhaust. Only thing is that a friend at the garage said that it if it was a cat it would normally be fine at idle but would show itself on acceleration. What do you reckon?

[merlin's S4]

Solved this now! Was a faulty MAF.