01 Jetta mass airflow

New guy here. I have a Jetta that I recently acquired. It will run with the mass airflow sensor unplugged. It will drive. But limp mode is triggered and it will barely run 60. If plugged in it will idle fine. But as soon as it’s shifted into gear (automatic) it runs for a second or 2 then dies. Slow to restart. Unplug it and it runs again in limp mode. The plug seems a little damaged, I have a replacement to splice in to try. I will update when I get a chance to do so. Just curious if this sounds like an expected behavior for maf/plug being bad.


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As is par for problems such as this, I recommend that you purchase or find someone with a VCDS so that solid information can be found that will tell you what your MAF is doing. Or rather, what the ECU thinks it is doing. If you see a damaged plug, then perhaps that is a large part of the problem. However, if you have different performance with the MAF plugged in vs. with it unplugged, then certainly all or most of the problem is due to a failed MAF itself.

The plugged/unplugged performance difference is usually a clue as to a bad MAF, but the sure way to tell is to graph the requested vs actual MAF values while the car is driving. You get that with a VCDS.

Good luck,

PH

Powder Hound said:

As is par for problems such as this, I recommend that you purchase or find someone with a VCDS so that solid information can be found that will tell you what your MAF is doing. Or rather, what the ECU thinks it is doing. If you see a damaged plug, then perhaps that is a large part of the problem. However, if you have different performance with the MAF plugged in vs. with it unplugged, then certainly all or most of the problem is due to a failed MAF itself.

The plugged/unplugged performance difference is usually a clue as to a bad MAF, but the sure way to tell is to graph the requested vs actual MAF values while the car is driving. You get that with a VCDS.

Good luck,

PH

Click to expand...

Thanks for the advice
I have a spare and will install with the new plug if I ever have a day off.


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Update. Replaced MAF with one off my crashed parts car. Spliced new plug in. Deleted codes. No codes again yet but car is painfully slow and at idle stalls when put into gear. (Automatic transmission)

Codes were
P0380 glow plug
P1144. Mass airflow
P1556. Low boost

It’s not throwing an accelerator code but is that possible? It’s just not getting full throttle? In neutral it revs slow but does feel responsive from start to finish. My golf sometimes went less responsive like this but it would be no different from half to full throttle (and only three a code once in 6 months of doing it about once a week).
Any insight is appreciated


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Did the replacement MAF come off a gas or diesel car?

Your low boost is why the car is low on power.
Are all the small vacuum hoses hooked up and not cracked?
You need a vacuum pump to check the turbo actuator if it's working correctly.
Search for limp mode here. It's mostly for over boost but the procedures for testing are the same.

The maf was off my 02 golf tdi.

I haven’t had time to get a vacuum pump and check the vacuum system. I’m sure there is a leak, I feel like I can hear a hiss. It’s kind of random tho. Sometimes it’s fine sometimes it throws a code. (I have been teaching my little brother how to drive with the car and we have been driving around a block or two every afternoon)

Here is what I observed about the stalling,
It only does it when the ac is on, the car is in drive, reverse, or any gear and the car is stopped. Neutral and park won’t stall with the ac on or off. It’s just like it’s not increasing the idle when it kicks on and stalling it out? Anyone had this happen? Could the vacuum leak cause this?



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Maybe torque converter locking up on you.

You really need a scanner but without, you check for vacuum, you should have 19-20", then get under the car and check for vacuum at the turbo, if you have that, then use a vacuum pump to check the can and vanes-check for full movement or any movement. Its possible you have a seized turbo or a bad can.

CrashedGolf said:

The maf was off my 02 golf tdi.
I haven’t had time to get a vacuum pump and check the vacuum system. I’m sure there is a leak, I feel like I can hear a hiss. It’s kind of random tho. Sometimes it’s fine sometimes it throws a code. (I have been teaching my little brother how to drive with the car and we have been driving around a block or two every afternoon)
Here is what I observed about the stalling,
It only does it when the ac is on, the car is in drive, reverse, or any gear and the car is stopped. Neutral and park won’t stall with the ac on or off. It’s just like it’s not increasing the idle when it kicks on and stalling it out? Anyone had this happen? Could the vacuum leak cause this?

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Click to expand...

Does it stall as soon as you put it in gear or randomly while idling or upon acceleration?

jmodge said:

Does it stall as soon as you put it in gear or randomly while idling or upon acceleration?

Click to expand...

When you put it in gear it dies. Just a few seconds later. If you shift into gear then give it throttle immediately it will drive fine. If you give it some throttle (like 1000 rpm, just a real fast idle) then shift it will drive fine. All 4 gears pull (it is a 4 speed right?)
The turbo isn’t seized I don’t think. I can hear it spool and the car has boost gauge that reads around 5 ish. Doubt it’s accurate, looks like a Walmart piece of junk and the installation job looks like a Best Buy speaker installer did it. Regardless, it moves.
Never dies when the accelerator has some input. It starts right back up when it does stall. It’s not a violent stall like dumping a clutch. It’s not real sudden like turning the key off. It’s as if the idle adjustment was just adjusted down to below a running rpm. Just slows to a stop over the course of a second or two. Ac works parked. Ac works riding down the road. If you turn the ac off while coming to stop signs, you’d have no idea it didn’t run perfect.


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so if the ac is off, no issue?

If you have no issue with the ac off, then I’d check the serpentine belt path. While it might be a failing ac clutch or compressor it might also be an alternator or alternator pulley, or belt tensioner or even a power steering pump that is going bad and turning on the ac just puts to much load on the engine at idle.

Tdijarhead said:

If you have no issue with the ac off, then I’d check the serpentine belt path. While it might be a failing ac clutch or compressor it might also be an alternator or alternator pulley, or belt tensioner or even a power steering pump that is going bad and turning on the ac just puts to much load on the engine at idle.

Click to expand...

If you turn the ac on in park it works perfect
If you turn it on while driving over 1000rpm it works perfectly.


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jmodge said:

so if the ac is off, no issue?

Click to expand...

Correct. Hasn’t stalled yet with the ac off.
(Since the pedal replace and the maf replacement )


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Update. Seems to be fixed. The [I’m guessing check valve] between the vacuum pump and the break booster had a port broken off of it that should have a vacuum line. I found the loose vacuum line and replaced the broken check valve and it runs like a champ. Still long starting(don’t remember if I even mentioned that), and occasionally when it is hot started with ac on, it will stall when put into gear. But cold it works fine and 5 minutes after a hot start it works fine. Guessing I’m getting air in the fuel supply line? Any other common long start causes?


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