Hoping someone might be able to help me locate an issue I'm having. The car is a 2005 Focus Ghia 2.0 (obviously petrol). A couple of days ago I was driving to work and the car started to feel very sluggish on acceleration - not jolting in any way as if to indicate fuel starvation, and the closest way I can describe it would be to say it was like driving with the handbrake on. A couple of minutes later the engine warning light came on. My first call to Ford proved unhelpful, with no mechanic willing to talk to me unless I booked it in for a diagnostic check at £85.00. So I called my local independent who have been great in the past with other cars of mine and they confirmed they could run a diagnostic for me. I took the car in the following morning - warning light still showing but by now the car was driving fine, until I got near the garage and it started going sluggish again.

Diagnostics indicated an issue at the inlet manifold but the garage could find nothing wrong with the car, which by now was driving fine again, and all they could suggest was that I approach a main dealer if I wanted to investigate the issue further. They finally reset the diagnostic which cleared the engine warning light. I picked the car up from them, it felt fine, and an hour later it was starting to go sluggish again. The following day the warning light came back on after 20 minutes, but the car drove fine, no issues at all!!!

I've now had the engine light on for a couple of days and what I can confirm is that when the car is running cold it acts normal, and it's not until about 30-50 minutes in to a journey that I start having this power drain problem. There are a couple of other symptoms which have ever so slightly started to appear - last night when I parked up I could smell the catalytic converter quite a bit, and I've had the odd exhaust pop and the engine overall sounds a little louder than normal, but not engine noise, more exhaust noise.

I know the issue has to be electrical, but I've no idea where to start and I'm keen to avoid expensive main dealers charging silly labour rates. I have read some stuff pointing at air mass meters which might explain the symptoms and why the error code pointed to the inlet manifold. I'm reluctant to just start changing parts when I don't know if they're to blame, but if they're relatively cheap parts to buy and easy to fit then I'm willing to give it a go.

I'd appreciate anyone who can take the time to reply with any thoughts or suggestions.