My 95 104 engined coupe will start well, and once it comes off it's higher idle[1000rpm] it will stumble and blow black smoke a idle.It also stumbles under acceleration, but will perform as normal under full throttle. The idle still lopes. I took the car to the dealer and they could not get any codes from the computer. They replaced the 02 sensor, no change. I checked the engine wiring harness, and found it to be crumbling, so I replaced it. No change. Getting expensive replacing good parts, can anyone tell me where to look next? Could the computer be a problem? The check engine light is not working, but have not yet had the dash out to see if it is just a bulb... Help!!

It's obvious from your description that the engine is getting too much fuel. This could be caused by any number of things. I would start by checking the ECMs ability to monitor its various systems, since you say there is no Check Engine light. This could be something as simple as a faulty bulb, damaged wiring, or even a missing bulb.

Have you owned the car long? Did the Check Engine light ever work before?

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1989 300 SEL that mostly works, but needs TLC

Sounds like the mass air flow meter is acting up. Only fix is to replace it, about $300

You can check the CE lamp by simply turning the key to the run position..
You can also check the CE lamp system by simply pressing the led sw at the diagnostic box and holding it for 2 secs w/key ON . Release and see if a code comes back. If it does , the CE should be lit.

Do a search on "led/sw" and also on "OVP relay"