Heres the deal,
My 206k mile 99 ML430 was pulling some MAF and fuel trim codes (170, 173). It made the car run poor, so I ordered a brand new original Bosch MAF (OE). The car ran slightly better after I replaced it, but the codes that were in the car wouldn't erase from my scanner, even if I went into the ECM. I unplugged the battery to reset the computer and fuel maps so the fuel trim wouldn't be an issue.
After a test drive, the car still acts poorly. Shakes on idle and sometimes acts like it wants to die out at idle RPM. A week ago we tested the car without the MAF in and it ran great. It was almost buttery smooth, its just that the throttle response was a bit wonky and the car would want to die sometimes at stoplights.
Did I just get a bad MAF? When I scanned for codes after the test drive P0100 came back . We reassembled it to make sure we didn't mess up the installation but it still acted the same, I also sprayed the MAF plug with contact cleaner and the MAF with MAF cleaner but really no difference.
Does the car just need a few more drive cycles to act normal or should I return this MAF, since it seems defective.
Also, this car doesn't act wonky after you unplug the battery like other cars. So its not acting weird because of that.
Something I forgot to add, I was looking at the live data and the load and intake manifold pressure seemed to be acting weird.
(All in Park)
The load % only would go up to about 13% at 3k RPM and the manifold pressure seemed to go down the more RPMs I gave it. Is this normal? Im not a data junky but I don't think thats supposed to read out like that. Does this car get it's data from load and intake manifold pressure from the MAF or MAP?
The load % only would go up to about 13% at 3k RPM
the engine shouldn't be working very hard in Park.
and the manifold pressure seemed to go down the more RPMs I gave it. Is this normal?
MAP depends on engine RPM and throttle position.
If you open up the throttle, and the engine hasn't revved up yet, you will have very close to atmospheric pressure (high). As the engine speed picks up, more manifold air will be sucked into the cylinders, and manifold pressure will drop. If you then snap the throttle shut, it will resist the air flow and pull a vacuum (low pressure).
Does this car get it's data from load and intake manifold pressure from the MAF or MAP?
the MAF measures the number of air molecules moving past the sensor (mass)
put the old MAF back in and see if the P0100 code goes away
Thank you for the comprehensive explanation.
The old MAF was pulling P0100.
so in that case the problem might be electrical, and not the sensor.
Either the wiring or ECM
I've had suspicions the ECM might be bad, though they usually never go bad on these cars. I'll have fun digging this problem.
yep dig up some wiring diagrams and get to continuity testing with a meter