Don't want this to boil over....

I just purchased a 1992 300-E with the straight-6 3.0L engine. I had a MB mechanic check
it over and had some minor work done. Replaced motor mounts and Serpentine belt. He
also adjusted the air/fuel mixture. I still experience a rough idle and have run 2-3 bottles
of STP FE cleaner through the system. I didn't drive the car "full out" as the mechanic
recommended as I didn't want to break anything. He also recommended I run 87-89 octane fuel even though the book recommends 93+. The car is great and I enjoy it very much. Just need to get rid of the rough idle. The mech said it looks like the injectors are
the new style and may have been replaced since 92. BTW the car has 103K miles. He
said in a worst case scenario the fuel distributor may be bad ($1000).

Would appreciate any other suggestions/experience?

Also...it takes a while for the tranny to warm up and shift at proper points. Fluid level
is good and fluid is clean (probably replaced within the last 12 months). A friend said
all older MB's do this??? He has a 87 380SEL that does the same thing.

Thanks,
Bruce

 

you got a bad mechanic, but a good car.

ask him take out those fuel injectors and check the spray pattern and quantity comparison.

use the 93 octane fuel.

yes, the fuel distributor is bad. cmscott is an expert on this topic, he have learned from good experience.

you don't need to warm-up the transmission to get it working normally.
the purpose of late upshift is to bring the catalyst or catalytic converter to warm-up quicker this is normal.

check the control cable adjustment (attached to the throttle linkage)