Well, first off....that part you ordered does not exist on the 1989 300E.....might as well return it.

The injectors are completely mechanical, no wires exist. Only the cold start injector has a wire, and I doubt it has any issues. The issue you are describing is caused by a faulty engine temperature sensor (at the far back of the drivers side of the engine with a big connector plugged into it) and possibly a stuck or gunked up idle control valve.

Since your ABS light is on, I'd replace the OVP relay before anything else, it could very likely be the cause of all your issues.

Your seller was feeding you stories....you can't "turn up" the idle on these cars, it is computer controlled. The whole problem is that the electronic injection and idle control system is not operating....and it is running on mechanical injection. Idle speed on mechanical injection is about 500rpm, if the electronic idle system is working then in park it should be around 700-800, and 600 in drive or reverse. And it should go to around 1100 when first started cold, then drop down after a few minutes of warmup.

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