Group,

I just picked up a 1989 240DL as a daily driver. It had a hard cold start and lumpy idle issue. It also would run lean at times. Within a week I got a Check engine light! Whoopee!!!

Initially I got a couple codes out of the OBD system. 212,121 and 231.

After doing some research I tried the path of least resistance, and cost. I cleaned The idle control valve, throttle body, AMM connectors (replaced by PO a year ago) and recalibrated the TP sensor back to spec. I also jiggled the O2 wires and tighted that connector. Threw in a bottle of techron and changed the fuel filter. Cleared the codes and the light didn't come back.

So now the car is only slightly down on power vs. my memories of my old 740GLE's power. It starts right up but still has a crappy idle when cold. The Check engine light flickers when cold and will brighten as the revs rise on cold acceleration.
Once the car warms up the light is gone and the idle only has a few dips a minute.

The car won't store any codes despite the flickering Check engine light, keep getting 1-1-1 from the OBD(No codes)

I'm thinkin' O2 sensor but want to hear any advice before I plunk down $100 for a new one since I am not getting any codes.

Any help would be appreciated.