Hi All,

I have a 93 300CE with about 187,000 miles. I’ve owned it for 16 years still love it like the day I bought it.

It’s been running fine except for a tiny roughness in the idle, but otherwise great.

Yesterday, drove about 20 miles on highway about 65 mph, stopped at a light and it stumbled and shut off. It started right up, pulled into a parking lot and it was idling very slow. Drove back home at highway speeds and was OK along as I was on the throttle. if I let off the gas, tach still showed 2000 rpm, but engine RPM was dropping. If I gave it throttle, there would be a big stumble and jerk and then pick up again.

Today, it started fine cold but idle was rough at about 500rpm. If I work the throttle with my ear near intake, I can hear a slight hissing/vacuum leak sound.

I ran the codes with my homemade tester and it is confusing:

using the button and light on the 16 pin diagnostic port I get: 6 (idle speed control faulty, 12 (Headed Oxy sensor circuit open or short, 19 (Injector circuit open or short), 22 (crankshaft position signal faulty). I can’t imagine it would run if all of this was going on!

Using tester button and light, yellow in PIN 3, I get code 6 and 22.

using PIN 14, I get code 2 (cruise control/ idle speed module)
and code 5 (stop lamp switch)

PIN 8 gives the No Fault Found code.

The CE light is not on.

Two years ago It dropped a cylinder. I replaced the plugs, connectors and coils that solved that problem. I do have a little trouble with the neutral safety switch where sometimes it has to be in neutral to start.

Other issue that has to be addressed is Catalytic Converter and pipes are original and have to be replaced now, but all I see is replacements in plain steel with one inlet/outlet converter, instead of stainless with dual converter.

I have opened up the engine harness in different places and wiring looks OK. Previous owner had throttle body replaced, head gasket and timing chain at about 120K.

Is it worth cleaning the throttle body, EGR tube and resonance valve just as maintenance at this point.

Sorry if I’ve gone overboard with long post.

Thanks in advance for any help!