Hi I'm new and hoping for a little help

Car: Merc. C 220 elegance 1994 petrol Auto UK model
Problem : Limp Home Mode
Turn ignition key = engine starts = idle climbs up to 1000 RPM then goes
into L.H.M. = switch of ignition = restart and the same thing happens.
the car used to travel approx. 15 miles before it went into L.H.M but by quickly turning the ignition
On/Off while driving you would get another 2 miles or so, I then lost interest and put the car on hold for a year
and bought a 1995 E200 petrol estate this had to have a head gasket replaced and now has a problem which is:
when cold and first started it drives fine but after a few minutes of running the idle becomes lumpy intermittidley
and feels like its firing on 3 until it picks up speed then its ok , meaning it drives fine on motorways etc until you stop at a junction and need to drive off again also I'm sure I can sometimes hear faint backfires when driving off from a standstill.
could it be the coils for the spark plugs breaking down and causing the excess fuel to explode.the fuel consumtion appears to have increaced.
thanks
Brian