Where do I start, owned the car for about 5yrs now and never missed a beat best one to date....so moved closer to my work so wasn't using it as much I SORN the car and let the MOT run out no dramas it was on the drive. Time had come to start using it again started 1st turn of the key fresh battery and all that idle was 100% no issues, as soon as you put load on the car it was back firing and really bad. Had the cruse/eml and traction control lights were on, did a scan and found misfire on all cylinders no other codes...so changed the fuel filter and drained the tank put fresh ron99 in it as it had been standing for a while, no difference still the same. Did the plugs today and what a pain in the **** that was........fuel pump will be next, but any ideas on what next to look for. thanks terry

 

id have a compression test done to rule that problem out.

 

Look for signs of mice. They can eat wires, hoses, in fact almost anything that's not metal.
Check fuel pressure and flow. Pumps can sometimes clog over time.