Recently been having a slight issue with my Fiesta Rs Turbo. Starts fine and runs fine most of the time but occasionally the car will all of a sudden start playing up. The idle drops real low to around 400revs and the engine will the car will start juddering like the engine is being "choked" with fuel. If I throttle the car while this is happening it will pop and backfire. Switching the engine off and back on again normally cures it!

It appears to happen randomly so proving quite difficult to diagnose. I took out the battery and put it back in to reset ecu and the car was fine for 150miles but now its started to do it again.

Any ideas?

Car spec:

1600 cvh, T28 Turbo, Ahmed Bayjoo 195 Chip, Mapped to 18psi, Beige Injectors