I got a 90 300sl that runs half way decent when cold, but when it get hot, it cant get out of its own way. I have replaced plugs, wires and the rotor and cap are three years old. the car is much worse when it is under load, (a/c on or in gear) idles fine and revs in nuetral fine. It feels like a miss, and I noticed when I try to adjust the plug wires, I get different results in how the car runs, but it never runs great. Is there a certain way to run the wires, or should i be looking elsewhere.

Pull the distributor cap and check for signs of Oil, I had an occasion where the O-ring seal on the distributor shaft was worn and when it warmed up and the oil got thin it snuck past the o-ring and foulded the distributor cap,

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Jerry

2004 SL500 Black 55K Miles
2002 s500 Black 90K Miles
1986 300E Gold 233K Miles
1966 Twin Cessna 320D
1989 Jeep Cherokee 233K Miles
1994 Ford Van E150 399K Miles

Time to check for vacuum leaks (especially idle control valve hoses) and to replace the wires with factory ones if you used aftermarkets -- three years is about all you get from aftermarket wires. The Bosch wires and cap/rotor will set you back around $175 bucks, but will last ten or more years. Also check for "burn" or "spiderweb" marks on the wires -- if you find any, it's a sure bet you have bad wires.

You should also screw the connectors back onto the wires at the plugs if you pulled them without properly grasping ONLY the connector -- the wires just screw on and if you pull on them, they are loose.

If the wires are OK (although I doubt it if you are having cross-fire problems), you have a mixture problem. This may be a large vacuum leak, or may be a bad oxygen sensor that isn't triggering the check engine light yet.

Dirty injectors will also do this, although usually that is only an idle problem, not a running problem.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

wires last week, plugs three months ago, rotor and cap three years old. The other ideas your giving me sound good, thank you.

it is dry inside cap and rotor, however the rotor didnt look great, but not too bad, i used sandpaper to try to make a better conection but nothing helped, i am going to look into the senser.