When I start the car, it runs great. When it warms up, the acceleration drops to the point that it doesn't have much power at all.

So far, I've replaced all 3 coils, the plug wires and the fuel filter.

Suggestions?

 

Try this,
All auxiliary systems must be off (radio, lights.aircon, etc) no electrical drains or CAN signals can be triggered during the process.

Turn the Key to the "on" position (the position right before you start your engine)

Press and hold your gas pedal down for like 5 seconds

Turn Key to "off" position (dont remove the key) and then release the gas pedal.
than wait at least 2, if not 3 minutes, for the system to reset.
You may see a marked difference.
Worth a try, and be sure the S/W switch is in the S position before doing it.

 

It could also be your throttle position sensor.
Used are around $45.00 on Ebay, and a lot more new

 

Don't know if this will affect anything, but when it's running poorly, it doesn’t want to downshift. I have to floor it to get it to downshift.

And once it gets above 3,500 RPM, the acceleration picks up markedly.

 

I have a 1994 C280 and has been exhibiting the same behavior for quite some time. I have done usual checking for vacuum leaks, disconnected sensors and have done the obligatory tune up. OBDII scan comes back clean and passes California smog testing. The throttle body and MAF have been recently replaced to no avail. I have tolerated this as I hate to start throwing parts at he car but am about to change the Oxygen sensor as this is original to the car and would certainly be "lazy" at this time. I'll report back when I get around to changing this part.

 

Looks like you have bad CPS, did you replace it recently..??

ZAYED,,

 

I have similar problem, does yours sound like a misfire sometimes?

 

No. It doesn't seem to be missing at all. Smooth, just slooooow.

 

It's never been replaced.