PeachParts Mercedes-Benz Forum - View Single Post - Rough idle for first 4-5 minutes on start up cold and hot

lsmalley · #8 10-07-2023, 05:05 PM

I retraced the steps last night, and decided to put everything back the way it was. I bought and replaced the air meter boot below the fd. The engine is a 3L and all the seals, rubber, filters, and injectors are replaced, including the fuel pressure regulator. Ecu is the same, but car ran fine before I recently tampered with it, so I put everything back, pre- my adjustments, even the air plate, the one thing that I can say that isn't back the way it was is the air-fuel mixture screw. I thought my method was correct, but though it made logical sense the way I did it, I'm not so sure. I don't have a dwell reader, so I used the voltages on the x11 connector positive lead of multimeter set to vdc to pin 3 and the negative lead to pin 2 (gnd), engine idling the numbers are jumping around from 12.5v to 12.7v. Before the numbers were 2.5v to 3.4v. I am unable to get those numbers now from adjusting the af mixture in any direction. If I try to get the number lower going ccw by minute turns, once it gets to where the numbers will drop, it just continues dropping until it idles way down and stalls out at about .07v or less. Not getting any codes though, however, fsm mentions that you can also get non-stored "errors" in the form of reading the on/off ratio. I know how to get to the on/off reading, but I don't know how to do it with just the multimeter voltage. Pin 2 and 3 shows 8.5v - 8.7v with ignition on engine off when car is not having any issues. I know that doing the koeo reading in a California car with no issues should show 85% duty cycle. So would that 8.5v be the equivalent using those pins on the x11 connector? Now that car has issues the koeo reading shows 6.4v - 6.7v on pins 2 and 3 of the x11 connector. Would that translate to about 65%? I'm not sure and I'm hesitant to go further down into the rabbit hole by making other adjustments without knowing if it would compound the issue. As of now the car is driveable, but I don't think I can make it even 200 miles on a single tank of gas. I will look at the plugs when I get home and try the suggestions from above as well.