1999 Mercedes Benz CLK430 Car Starting and Performance issu

Rarely my car will have problems starting. It starts and dies. At one point, it completely wouldn't stay on and I had my fuel pump replaced. Problem was gone for 6months.
Now its doing it again (rarely). After getting it to start by revving the car up at start-up, I noticed that I cannot get it to rev past 4000 rpms (not red zone). It starts sputtering, and almost makes a coughing sound, and the engine shakes.
Car has been running a bit rough. I did rev it past 4000 rpms after the incident above and I didn't notice it stalling then or having any issues. But I am a bit concerned.

I'm thinking changing out the spark plugs/wires. Is that a good start? Any other possibilities?

Also of note, my 'check engine' light has been going on/off every few weeks for 3 yrs. Took it to 3 shops, all said no worries, just a sensor. Even changed a sensor once but light came on again in a few months.