Hi,

First post, so hi to everyone and hope you can help.

Got a 53 plate ST170 and it has recently started to intermitently hesitate generally in the higher rev range, i.e. 5k upwards. Seems to be worse when the engine is under load.

Seems to generally be OK from cold but after driving around for a while the issue starts again.

I have had the IMRC replaced, I thought the transition from long to short runners could have been causing the hesitancy given it was at the higher end of the rev range, no chnage.

I noticed from the docket from my last service they put in the wrong spark plugs, should be 1151999 but they had used 1233897 which I believe are for the standard 2 litre. Had the plugs changed for 1151999 by Ford for free given the error on their part but still no change.

I have once had hesitancy between 3k and 4k Revs, the engine management light does not come on and my mechanic checked and there seem to be no error codes recorded.

I am next thinking of HT leads and coil pack, any other ideas ?

Thanks in advance.

Mark