My Focus is a  Mk2 1.8 Style 59 reg and has the following issue.

In 1 start out of 10 the engine starts but instead of idling at around 1000 revs, it only reaches 500 but no power transfers from accelerator to engine and for roughly 30secs it stutters before kicking back into full idle revs and with full pedal reaction. Most often this is on a warm rather than cold start. So far, no diagnostic fault shows up because it performs perfectly well on the ramp.

I sense it's becoming more frequent and that this is an engine management issue - or, as was the case with a Nissan once, a fuel sensor.

 

Any ideas would be appreciated.

Cheers,

Ruskin.

 

Just a guess but it could be throttle position sensor. You need the codes read.