I drove a 2008 1.8 tdci that had the symptoms you describe; I think the throttle pedal actuator was faulty. There was a lag between pressing the pedal and the engine responding. This worked both ways ir the throttle remained applied for ~0.5s after you lifted off which made changing up gears rather tiresome.

Is it only after a hard drive that you get the lag?

I had a 2008 2.0TDCI (140bhp) Zetec for over 3 years and I seem to remember from the Ford forums that there was an engine management update for the early 163bhp 2 litre engines to fix throttle response issues, but I'm not 100% certain. Try a search of the TalkFord.com site under the Mondeo Mark IV diesel engine section.

The 1.8TDCI mentioned by Unthrottled was notorious for laggy throttle response, there were a couple of ECU updates to fix it.

On my own car, the pipe from the intercooler to the inlet manifold was badly fitted at the intercooler outlet. It was weeping oil mist and was a swine to get at. I managed to fix it by removing the driver's side headlamp which gave me access to the hose clip. After skinning a few knuckles I got the pipe properly seated on the spigot and nipped up the clip properly, which improved throttle response and fuel consumption.

Edited by craig-pd130 on 10/06/2013 at 23:08