OK, I could really use some help with the occasional stalling and bad engine surging. I built the code reader and spent some time under the hood this yesterday. Recently new parts, OVP relay, plugs, coils, wires, and fuel filter. This was all part of normal maintenance over the last couple of months. Recently replaced the fuel pump relay and fuel pressure regulator in an attempt to solve the surging and stalling. I do not have any engine codes as a result of the problems. If I unplug the MAF the car runs well except for a hunting idle do to the MAF being unplugged. Then I get codes on Pin 8: codes 4, 13.


This car is a 1993 49 state model with the 104 2.8. It has 53,000 miles. It does not have a CE/MIL light, does not have a built in DM LED/pushbutton, and pin 3 of the 16 pin connector is empty. So I'm assuming it doesn't have the diagnostic module functionality...

I cleared codes and reset adaptation values and plugged in the MAF. Took car for a 10 minute spin. Ran great for the first 9 minutes. Then all the same symptoms returned: intermittent wandering idle (500 - 1100 RPM), surging at cruise, and a hesitation when first tipping into the throttle. Pulled codes again after drive testing and did not receive codes.

Not quite sure how to proceed from here.
This car has a newish wiring harness being replaced in 2000. No record of O2 or MAF replacement. If I cannot find a vacuum leak perhaps a fresh O2 sensor is the next step? I'm open to suggestions.
Checked the fuel pumps today and one of them is leaking an oily residue? Is it going bad? Would this cause the symptoms?
Thanks,

BILL

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87 560 SL
93 300E 2.8
91 300CE-24