Hello all! Longtime lurker, first time poster.
I have a 94' e500 with 110k miles on the clock that could use your help. It has an updated upper wiring harness, original lower harness.
Over the past month or so I've been experiencing an issue with an engine misfire while driving. The vehicle would be at cruise (say 45mph) at light throttle to maintain speed and the engine would suddenly feel lean for just a moment and then return to normal. Over the course of a month this issue manifested into a more prominent but momentary "blip" in power, and now to a rather severe lurch while at partial throttle. Heavy or WOT the car pulls fine. So I don't it's a fuel starvation issue.
I started with the usual suspects: caps, rotors, plug wires, and plugs. I installed new bosch caps & rotors, and F8dc4's. The insulators are original but in fine condition. The wires had already been replaced by the PO with Bremi wires. All appear and feel new, though in typing this I just realized I haven't actually checked their resistances. No improvement with the issue after the above changes.
Next I suspected the ETA. It's original to the car (93' production date), so I replaced it with a shelved unit that I picked up from a junkyard a year or so ago. It's an old unit as well, but since I had it on the shelf I figured I'd try it out. Once installed and calibrated, I test drove the car. No change in run quality (though it does rev' a bit higher on startup which is neat). I replaced the throttle body boot and the the PCV hoses during the change too.
So next I did what I should have done from the start and pulled the codes. This was new for me, as I've only ever used the DM module LED blinker. This time I tried out the HFMscan software/ adapter to pull the codes across all the modules. Two codes were stored: 004; and 010. I've paste'd the readout below:
4 Voltage at air mass sensor with hot wire.
Voltage too large/small or ground cable at air mass sensor
open circuit. (The fault may be ignored on vehicles up to 07/91)
Verify voltage at air mass sensor with hot wire.
While IGNITION=ON = 1,0-1,2 V - ENGINE=IDELING = 1,3-1,7 V.
Verify also the ground cable for sensor. (While IGNITION=OFF < 6 Ohm)
10 Idle speed recognition from electronic accelerator pedal faulty.
Control unit has short circuit.
Verify idle speed recognition signal voltage from EA pedal actuator.
While IGNITION=ON, and accelerator in idling position < 4,8 V
While IGNITION=ON, and accelerator in full throttle position > 5,5 V
On vehicles up to 7/91 fault may be displayed although no fault exists.
Looks like a fault with the MAF sensor, and what I believe is the momentary switch above the pedal? I think I saw another post on here about an issue with that. I'm new with HFMscan, but I'm pretty sure it pulls fault codes from all modules right? Not just the diag module.
Before I throw more parts at my problems, what do you guys think?
I did try driving around with the MAF unplugged. But I experienced the same issue.
Open to all thoughts and criticisms lol. Thanks!