Hello,

My 300e ('89, 130,000 miles) runs fine when the engine is cool during cool
weather but during warm weather when I come to a stop after running
continuously on the highway the engine will miss on several or all cylinders
at idle but not die.  Usually this will stop after I drive moderately around
town but it still happens occasionally on a hot day when I'm in town.  I
have also seen this happen after being parked at an idle for about 20
minutes with the ac on and the problem got progressively worse until the
engine almost died.

I have replaced the fuel filter, fuel pump (one of two), fuel injectors,
spark plugs and wires, distributor cap and rotor within the last six months
so I assume these aren't part of the problem.  I have a new coil on the way
but somehow doubt that that's going to help much.

My mechanic thinks it's the oxygen sensor (hasn't tested it but says he can)
and has suggested I first try a bottle of fuel additive in a tank of gas to
see if that helps.  I did just have the valve stem oil seals replaced
because the plugs were fouling in 3 or 4 months.  Could the O2 sensor have
been affected in the same way as the spark plugs and be causing this
problem?

Many thanks,

Mike