variations of speed on a constant throttle

[CERBY8]

Hello all, I have a 2008 Focus St with only 15000 miles on the clock and it varies speeds slightly on a constant throttle, does not always accelerate cleanly and runs smooth with either quarter throttle or full, with nothing much in between. So take your time or go flat out.

Any feedback welcome

[TRUENOSAM]

sounds like turbo lag to me. Failing that have you had the codes read for any underlying faults?

[Geezer-20v]

I'm no expert mechanic, but have you checked Ignition coils, HT leads or plugs?

Could be that it is missing slightly.

Or you could take it to a garage and have them plug into the ECU and check for any fault codes.

[GravelBen]

Sometimes a slight surging feeling on constant throttle can happen with turbos (more so than NA engines) if the road is undulating - a rise increases load which increases boost, then it drops away again as load decreases on the downhill. If it feels significant there is probably something not quite working properly though.

[CERBY8]

I have had the plugs changed and it to Ford who had the diagnostic machine on and showed no faults, its too slight to be turbo lag and I think it might be the throttle switch

anyone had experience of this, thanks for your replies so far

[worldsend]

Have you got the aircon on? I find the compressor switching on and off is very noticeable in my 06 ST. It's a real PITA, and much worse than any other car I've driven.

[Ry_B]

I'd say it's down to the turbo and wouldn't worry

[MondeoMan1981]

Do you mean totally constant throttle on the flat ? If you are going over any undulations, bumps, cambers etc as your car gets moved around, you get moved around. Depending on the tension on the throttle pedal... it could be your foot !

[CERBY8]

Aye on the flat and you feel it more at 70mph and above, its definately not undulations in the road as the throttle isnt that sensative

[HellDiver]

I get the same on my car - 1.8 Duratec powered Mondeo. Light throttle up a hill it'll surge and slow - say 3rd gear at 40mph it'll stutter and surge, I'm assuming it's to do with the EGR.