m103, timing issue?
 

1990 300SE. My car seems to have no power and all until it hits 3500 rpm. Once it's there, it feels like it always has. Wasn't a gradual thing, just happened all of a sudden. Seems like the same exact issue you'd have with a bad vacuum advance. It starts perfectly fine, and idles great. But once it's under load, it struggles, bucks, sputters, and threatens to stall until it gets up to speed. I feel safer with it on the freeway than I do around town. Hooked up the vacuum gauge, appears normal. Every once in awhile I'll get a pop from the intake.

Plugs are brand new Bosch h9dc's, gapped at 0.32. Cap, rotor, and coil were replaced recently. Wires probably need to be replaced one of these days, but like I said, it really happened overnight. Doesn't matter what temp the car is at either.

I'm ruling out a clogged cat because I have plenty of power on the highway. Same for fuel pump + filter (even though I have a spare fuel filter I'm going to replace tomorrow for good measure).

Haven't checked the timing because I can't find my stupid timing light. Probably grew legs a long time ago.

Also, drove for a few miles with the vacuum line to the EZL unplugged. Didn't make too much of a difference, just felt a bit like more of a dog at low revs.

Any ideas?

Bump.

No ideas? Anybody?

Could be worn tracks on the airflow potentiometer.

Check all your vacuum lines including the one to the EZL ignition controller.

http://mb.braingears.com/126_DISC1/program/Engine/103/15-510.pdf


Check group 15, subgroup 500

http://mb.braingears.com/126_DISC1/program/engine_300SE.htm

from:

http://mb.braingears.com/126_DISC1/program/matrix.htm

One more thing, check the connection under the CIS unit to the throttle body.

The CIS feedback position pot is also a good place to check as stated previously.

on/off ratio
 

Can you read the "on/off ratio" of the fuel control unit?
If it is a fixed reading, a fault may exist.
This may lead you to the problem.
I agree that the air flow pot may be bad.
It can be tested with an ohmmeter. It should not go "open circuit" at any range of operation.
dpk