Hey everyone:

I just bought a 1990 240DL, which I like very much. It's been well maintained, but it has some issues I'm in the process of repairing.

First of all, it has a "hard" check engine light, meaning it's lit the entire time the ignition switch is on.

Next, it has some running issues which I'll describe as well as possible: When it's started cold, it starts quickly, but after a couple seconds stumbles and tries to die.It also has a pronounced stumble immediately off-idle.

As it warms up, it starts and idles good but the off-idle stumble is still there, just not as pronounced.

The third symptom is a barely-detectable surge at part-throttle cruise speed. It's barely noticable, but it's there.

Fourth and final is a LOT of spark knock at part throttle.

I pulled the trouble codes and got 1-1-3,1-2-1 and 2-2-1.

I checked for air and vacuum leaks and found *almost* nothing apparent..however, I'm almost sure I hear a vacuum leak somewhere below the middle 2 injectors. I've checked hoses and sprayed around everything and I can't make it change.

I cleaned the flame trap, cleaned the throttle body, cleaned the idle motor. I checked for a leaking fuel pressure regulator and that came up negative.I temporarily bypassed the hot air tube at the manifold.

I checked the resistance at the meter between terminals 2 and 3 and got 3.1 ohms.If I unplug the meter, my car runs WORSE(rich), not better.The car never smells rich otherwise and the MPG seems good.

I'm sorry for this being so long but I wanted to get all the info out there.Thanks very much.