I have a '93 300E 3.2L, and upon cold start, my car will shudder for about one minute and then smooth out. If I try to put it in gear before the air pump disengages, it dies.

How do I know my air pump (smog pump) is going bad? I replaced it about 40,000 miles ago. Could it be failing again?

Year & model car??

In most cases ON Mercedes Benz, the air injection system is for catalyst warm-up

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

It's a '93 300E 3.2L

It's probably just anecdotal that the air pump turning off coincides with the improved idle. All the puump does is blow a little air into the exhaust manifold to help heat the converter. Of course, the pump might be failing and creating enough drag to pull the engine down; but that's very unlikely, the engine could shred that small pump at idle and never even notice it.
To quickly check the pump, just unplug the wire going to the clutch in the front of the pump; it will then run on the idler bearing like the AC compressor. You can plug/unplug it and listen to how it runs and tell if there's an issue. If there is, just leave it unplugged, engine will not care.

Your problem may be in the cold-start valve - but I'm not an expert on that motor, let's see what Doc says.

DG

This model doesn't have a cold start valve. I will try to unplug the air pump, though, and see what happens.

Thanks for the input.

On that model the air pump should not make any difference in running cold.
IT is only a catalyst warm-up device.

SINCE it seems to make a difference there could be an issue with the coolant temp sensor OR internal ECU problem.

Have you tried running the car with the pump disconnected.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I tried running the car with the air pump unplugged, and things SEEMED to be a little worse, but not much different.

Also, now that the weather is reaching highs around 80 degrees, it is very difficult to even get it started. I thought it would be better when it's warmer, but it has become MUCH worse.

Any thoughts?

Also, the exhaust fumes seem to be overly strong when around the outside of the car and sometimes in the car.