Failed another smog test with my 1991 300CE @180m. I failed once before 2/2008 @ 148m. That one was due to high NOx and I needed a new EGR vavle, solenoid and the tube cleaned out.

I took it in pretty hot and there was no wait so it went right to the test stand. My start had become a bit more stumbling as of late but was OK when hot.

At one time or another over the years I have changed the following:

IGNITION

Plugs
Coil
Battery
Cap
Rotor
Temp Switch

FUEL

Fuel accumulator
Pumps w/ check valves
Fuel Filter
Injectors and seals
Cold Start Valve
EHA o rings
Fuel Distributor o ring

ELECTRICAL

OVP
CPS


AIR

ICV
Air hoses under throttle body
Smog Pump w/check valve and hoses
Air filter
O2 sensor
EGR and solenoid


After each of these changes, the start was never any better, always with a short delay and stumble. Recently the start deteriorated to a stumbling chugging start particularly when hot. A new cold start valve seemed to bring me back to the before stumble start.

In reviewing my records, I've never changed the wires, so I really should try that.

Any other ideas?

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