I've just taken my forged 2.5 blob out for a quick spin,on a nice long straight I gave it a bit in 3rd gear,looking in my mirror I saw a big cloud of black smoke so I came up to the next round about and dropped into neutral,the revs were dropping to normal then shooting up to around 2000rpm then straight back down to normal then back up again.

I pulled over and turned her off to have a look,couldn't see anything wrong so started her up,she stared fine but the idle sat at 2000rpm for about 7 or 8 seconds and then dropped down to normal idle (similar to cold start)

She still drives fine and the jumpy idle has now gone but when I rev her there is a grey/black smoke coming from the exhaust

No Eml/temperature fine/oil pressure and temp fine

Any idea?

 

I'd check the fuelling. Black smoke is normally an indication of over fuelling and would possibly explain the over revving on tickover.

Oil is white/grey smoke.

 

OK thanks, the car has just been all over the east coast covering around 400 miles and everything was fine,parked her up for a week and now this happens

 

Strange.

Pull out the dip stick and give it a sniff. Hopefully you won't smell any petrol indicating borewash/drastic over fuelling.

 

Sticking throttle valve?

 

I had the same on my wrx. It turned out to be a stuck idle control valve.

 

how would that cause the smoke when revved though?

 

Messes up the fuelling. Try taking it off and give it a clean

 

Yup, if the IACV doesnt return to its closed position it can cause all kinds of issues as it is letting excess air in, I think yours is a stepper motor so wouldnt hurt to clean it anyway

 

ok i will get it cleaned, just hope there is nothing wrong with the engine itself