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Old 09-09-2018, 02:11 PM
oldskewel oldskewel is online now
Join Date: Nov 2014
Location: SF Bay Area
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Originally Posted by mpouliot View Post
But oldskewel,
Running the vehicle while in "limp mode" is bad too, isn't it?
The fact that it "runs" better would point to the MAF, wouldnt it?
It "drives" worse without it plugged in, due to the tranny issue, but it "runs" better with the computer estimating the Air Flow without the MAF Sensor.
My basic comment / thinking is to try to help you to consider the problem in a simpler way to help you solve it.

"limp mode" - does that mean "TRANS. FAILSAFE PROG"?
If it does, from what I could tell from watching my car idle and drive, the engine ran perfectly. I doubt it was harming anything. Like I said, surely it was less efficient, and less powerful if I were to floor it. But the ECU is apparently capable enough to estimate airflow based on all the other sensors it has to make things run well enough. There was a noticeable clunkiness in the AT shifting, and I would be concerned about driving it with more power in that mode - worried about the AT getting damaged.

And I am absolutely NOT suggesting you don't have a problem with your MAF. You might have a crap MAF as upallnight and others are suggesting. I am not disagreeing with that at all. If I had one of those crap MAF's in my car, it would run like crap. Then I'd unplug it and it would run perfectly except for the AT failsafe trigger. How easy would that diagnosis be?

By unplugging the MAF, you take it out of the problem. Once unplugged, unless it is physically blocking airflow, the car should run fine - as I've explained and tested for you on my own car. So if you still have engine problems with the MAF unplugged, you've got problems other than the MAF. And if you find and fix those problems to make the car run well again (yes, again, this should be possible), at that point you can plug your MAF back in. Maybe it will run fine, or maybe like crap. At that point, diagnosing the MAF should be pretty simple.

So the debugging concept will have taken one complex situation, and reduced into two simpler ones just by unplugging a connector.

If the MAF is fine and working, then it may be able to mask some of the problems with the rest of your engine - again, making it harder to find them.

And I really don't follow your questions quoted above. Are you talking about my car, your car, or in general?

For example, separating "drive" and "run". It's easy for me to feel changes in this, since my car basically does everything perfectly right now (just finished engine rebuild). But in my explanations, I tried to separate how the AT shifting feels (would lump that into "drive") vs. how the engine rev, smoothness, power feels (would lump those into "run"). Separating variables might help your diagnosis.
2001 X5 3.0i, 190k miles, AT, owned since 2014
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