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?