I recently purchased an mk6 fiesta 2002 plate.

It's been driving fine without problem up until this morning.

The car started on first turn of the key but cut out as soon as I let the key return to idle position. I tried again and same issue. I tried whilst revving and the car was running until I stopped revving and cut out again. I then tried again with revs for a couple of minutes and stopped and the engine was still running but running up and down on revs on the dash.

I tried putting the car in 1st gear but there was a lot of resistance. Pushing against the resistance caused the car to start moving slightly forwards. This was the same for all gears. Reverse was crunching when trying to put into gear.

I left the car on the drive all day and when I got back from work it started on first turn of the key and was running fine. I put the diag machine on it and it returned a p0030 error which I've read could be o2/lambda sensor?

Tried putting into gear and was still some resistance although not as much. Turned ignition off and started up again and gear selection was working fine. I've took it round the block and tried every gear with no problem.

Diag machine was showing MIL was on but no lights on dash. Removed the unit and found some foam had been wedged in the recess where the MIL light should be - the light is currently permanently lit.

Had a look around in the engine compartment but not entirely sure what I'm looking for. I did find a sensor hanging under the car which after googling the part number I believe is the temperature sensor.

Anybody have any clues on what to look for? And why would oxygen sensor stop me being able to select any gears?

Thanks

The lambda sensor won't have any effect until the sensor is warmed up, so wont affect starting when cold.

The heavy resistance when trying to select gears will be a mechanical issue, whether it be the linkage itself or the clutch.

I did assume there were two problems but seems too much of a coincidence for both to appear and disappear at the same time. If it was gear linkages or anything mechanical it wouldn't disappear after being left for 8 hours?

Started the car this morning first time and gear selection all fine. Engine management light is still lit though.

Speed sensor ? TDC sensor ?