Rough Idle until 1000rpm, slight vibration in gas pedal at 55mph/2000rpm on highway

[north560sel]

Hello all,

I just purchased a 1988 560SEL from a private owner and drove the car home nearly 1500 miles. I had the belts and fluids replaced before I left for home. None of these problems were evident where I purchased the car so I wonder if the heavy driving made the seals on just about everything (lol) leak? I did use 87 the first time I filled up (but past 1500+ miles ahve been all 91) so I will try injector cleaner the next time I am low...

Engine runs rough when it has been running. It seems worse hot than cold. Also the starter takes too long sometimes.

I replaced all spark plugs and wires, the two closest to the firewall were pretty grimey/caked in oil. I wonder if the valve seals are leaking? Is replacing these a do-it-yourself job? Would just replacing the valve cover seals solve anything?

Also I am led to believe a fuel issue contributes- I can smell fuel when using the air conditioner at low speeds and fuel near the rear of the vehicle. I will replace the fuel filter as soon as I can find one (rare in small towns have to special order). However would the fuel filter have anything to do with the smell from the air conditioner since its near the rear of the car? Or do I have a bad distributor or E.H.A. valve too?

One last thing- there is a slight hesitation/vibration in the pedal at around 2000rpm/55mph on the highway, but when I speed up it tends to go away.

Thanks for any suggestions-