The car is a '91 300E 2.6 with 150k miles. Recently had the fuel filter clog up and had to change it. Afterwards, she ran better than ever to be honest. A couple of weeks ago, however the car developed a serious stumble, hesitation and misfire. I thought it might be the fuel filter again since that last one was so clogged, so I changed it again. No better. The car starts with little to no excess cranking every time. There is however no power. Low idle speed, it’s barely 500rpms. When you go to accelerate it will almost stall, jerk and shift hard with sputtering and bucking. Coming to a stop the car will try to stall out. Little to no power.

The check engine light had come on when the original fuel filter failed and was giving me code 17 for O2 sensor heater. Since the car had been running ok after the filter was changed I had taken my time getting to change it. After the car started acting up, it also threw a Code 22. Thinking this may now be the cause, I replaced the sensor. Had to go with the Mustang sensor route because no one had the right one here on the island. Even the dealer was over a week out and at $300. After installing it the check engine light did not go out and the codes remained. Car also ran the same. Went back and resoldered the connections and reversed the white leads. No check engine light, no codes, but car runs the same.

Pulled the plugs. They were fouled with carbon. Cleaned and reinstalled. Still the same. Checked the wires at night and saw no arching. Checked the lead from the coil, blue spark up to 1/4 inch. Replaced the distributor cap, it was toast. Car is still the same. Went ahead and put in new plugs, wires, cap and rotor too, but no better.

Replaced hose to idle control valve because of a leak there. I have a looked for other vacuum leaks, but not found any so far. I did pull the idle control valve and sprayed it with cleaner. This actually gave me the most improvement so far, but only marginally. The car is still not drivable. A few days earlier I had to take it a few blocks to get gas and it was pretty scary. The check engine light came on while driving again, with a code 17. Cleared it and it hasn't returned, but I haven't pushed it either.

Went back to the O2 sensor and checked it following Ps2cho’s guide. I got correct readings for the heater wires, but when I probed the sensor wire, things didn’t look right. I got .45v before starting the engine, but once started; voltage ran slowly up to .8 and stayed there. No drop, only a little fluctuation of a couple hundredths. So I figured that the new sensor was shot and ordered the correct Bosch one. Just installed it, and no difference, and getting the same readings on the dmm as before. Runs up to .80 and holds there.

So, has anything come up that point to a specific direction to follow up on? The one thing that sticks out for me is that the car starts with just a turn of the key. No excess cranking even if it stalls out. When it first starts up, and you put it in gear, it starts to move as if nothing is wrong. But almost immediately it starts to bog down and jerk into the next gear. After that it consistently stumbles on take off and stutters at high RPMs. Seems to be running very rich. The plugs were carbon fouled and the o2 sensor I had first replaced was completely sooted up after only running while I have been woring on it. Parts are starting to add up and each round takes a week or more to get here. I’ve been chasing this for over a month now. Any help will be greatly appreciated.