86 300E hard to start and runs rough
 

Great site, and I hope someone out there has an answer to my
mysterious problem.

I have an 86 300E, 5 speed manual (145K miles) that now refuses to start or
when it does it runs very rough. Another symptom has been that when it sits unstarted for a week or so
it would start, run rough, quit after a few minutes then after it sat for
a few hours start up and run fine. The last time it sat for a week it just
refused to start and is now at the mechanics. It has been at my mechanics
for a month and he has tried:
new plugs,
check the fuel pressure, says it is good,
checked both the fuel pump and overload relays
tried a new control unit from another 300E along with a few "rebuilt" ones.

Nothing seems to fix it.

My other ideas are: O2 sensor, and wiring harness. Mechanic thinks there
is a timing problem but I am not so sure given previous history above before
the latest problem.

Help!!

It's time for you to replace those brittle vacuum hoses under the hood.The vacuum lines are sold at autozone for 99 cents a foot. $2 should get you enough line hose. A bottle of Techron in the gas tank is recommended. Get a new air filter, and clean the throttle plate with carb cleaner.

Thanks, I hope it is that simple. Sure has stumped my
mechanic.

Symptom sounds MOST like intermittently plugged injectors. Best case, run a couple bottles of Techron/full tank, hope it helps. If not, a complete purging of the fuel system and replacing the injectors may be necessary in the extreme case.

Steve