Don't discount the cap/rotor.
 

John, I had a similar problem with my '90 300E. I had installed cap, rotor, wires and plugs 10k ago. Problem was I mis-fitted the distributor cap o-ring and it caused an improper clearance between the rotor and cap which caused massive arcing. It only did it after a long drive and was not noticeable at speed. Symptoms sounded like yours. Check out the thread "300E misfire when hot" last posted around 12/6.
Chuck.

http://www.peachparts.com/shopforum/showthread.php?t=171798

Here's my saga. Fixed by a cap and rotor after all else failed.

well i did my cap and rotor about 3 or 4 k ago, but that could be it. i remember putting the o ring i ordered in the groove but i dont remember any other o ring in there, tomorrow i will check that if the coil does not fix the problem. i had read that thread a while ago befoe i began this one and it sounded similar so its certainly possible. thanks again for all the help guys ill post tomorrow and let you all know what i find

You might also look for vacuum leaks. The idle air bypass hoses may need to be replaced. The rubber boot under the fuel distributor and throttle may be bad. The injector seals may be bad. It's an '87 after all.

Check the following links:

http://www.peachparts.com/Wikka/M103VacuumLeak

http://www.peachparts.com/shopforum/forumdisplay.php?f=82

http://www.peachparts.com/shopforum/forumdisplay.php?f=84

Just a thought.

tried replaced coil to no avail, but i plan to check out chucks suggestion tomorrow or later today if i have time, thanks for the help

Could be crankshalt sensor,that it screws up when it gets hot,also a big possability a coolant temp sensor. .

so the things so far i know its not...
coil
transmission
02 sensor
KE unit
plug wires
things it still could be
ignition module
still haven't checked the cap and rotor
cats?
vacuum leak
crank sensor

interesting, cap and rotor would have been the first thing I would have checked just because you can and it's fairly easy.

When were they done last?


Jonathan

Again....make sure your gas tank is venting.

My 560 front cat partially disintergated and rotated in its housing blocking gas blow. Systoms are different from yours. Highway is tough because the gases can't get through the blockage. stop and go was fine acceleration was gone. No back fireing or stuttering. Just no top end.

the reason i have delayed in checking it is it was done less than 3k ago about 6 months, and the problem didnt start until recently, but its next on my list over the weekend. how do i check the fuel tank vent? thats what i was wondering about on the cat, so maybe i can cross that off the list since the car passed emissions with flying colors when i got it and that sort of thing doesnt just happen all of a sudden does it? next stop, cap and rotor

Try this: Unplug the EHA and see if the problem persists. If the problem goes away, that eliminates spark issues and the mechanical part of the FI.

My daughters '87 300E had random bog and rich running issues. It's running fine w/o the EHA plugged in. Now to find the time to chase what's actually causing this.

unplugged the EHA and no difference, took the cap and rotor off and this could very well be the problem, theres some green stuff around the edges, and sure enough when i looked back behind the orange o ring i saw another black o ring that had hardened... any thoughts?

Sounds exactly like what I had. It looks like we both made the same mistake when replacing the cap and rotor. There should be one o-ring around the base of the "backing plate" (where you found the black one). I had installed the new orange o-ring and left the old, black one in place which apparently caused improper clearance inside the cap. I put new parts in and so far it runs great.
Chuck.

im awaiting the parts now, so much for 3 day shipping...:confused: the main thing is how long after you installed these parts did the problem start?? hopefully this will resolve a problem that has basically made the car un-drive able.