no power -only go 10 mph
 

I have a 1991 190e that will barely run. I had a muffler shop check the cat converter by cutting both pipes coming in to it but did not seem to help. The car will idle ok but when you give it gas it will not rev up and sounds restricted. I did put a new fuel pump relay , fuel filter , and plugs on it recently also.

Did the symptoms appear suddenly, sometime after replacing the above parts, or was that an attempt to fix the problem? Were there any other symptoms before the current one?

Did you see this thread?

Haasman

The problem started about three weeks after I put the fuel pump relay and filter on. If I push the accelerator to the floor, 1800 RPM is the maximum it will reach. When I rev it up or try to drive it a popping sound like a backfire comes from the cat converter and the cat gets extremely hot and starts smoking by the time I drive it a mile. Thanks for any advice.

Some of these cars have 2 sets of cats, you may see the precats up front by the exhaust manifolds. To check for restricted exhaust, just loosen the pipes at the manifolds.
You could also be dumping fuel into the exhaust, like by a misfire on a couple cylinders. Does it idle OK, or does it miss? The raw fuel dumping could cause the cherry red cats.
Another reason I've seen for a misfire like this is a broken ignition rotor bracket, throws the timing way off but surprisingly the thing'll actually run.
If none of this pans out (or maybe even before trying some of these suggestions) you could do a quick compression check.

Gilly