# Engine Dies As Soon as MAF Plugged In



## diamono (Apr 26, 2008)

*Intermittent MAF Issues*

Note: Changed title for better clarification.

I have a 99' Beetle with the 1.8t. I did an fluid and filter change on the 01M transmission and after I was finished, I could not get the car to run with the MAF plugged up. Unplugged, it runs pretty smoothly. I can't find any obvious vacuum leaks. If I have the air filter off, the vacuum is plenty strong enough to compress the bellow intake hose if you start blocking it some. I tried a spare MAF I had and it wouldn't run without gassing it quite a bit. I even installed a brand new one with a new housing and it's no better. If I get the RPM up around 4000 where it will get steady and quit bouncing around and very slowly let off the gas, I can get it to idle, but as soon as I touch the gas pedal, it'll die. VCDS shows decent MAF readings and they'll change according to where the gas pedal and rpm are at. Numerous TBA resets with VCDS also do not appear to help. Really confused at this point as to what could be causing this. Prior to the fluid and filter change, I did have two occasions where I started the car and it died immediately. Both times, I restarted giving it a little gas and all seemed well, so the fluid and filter change may not be related, but just happened to occur at the same time something else was happening.


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## rstolz (Jun 16, 2009)

check your fuel trim.

unplugging the MAF results in the ECU to run a default fuel map that ignores the 02 and MAF readings. It adjusts to an overly rich mix. Ok for short durations but you don't want to run for a long time like this, as it will eventually destroy 02 sensors, cats and foul plugs.


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## diamono (Apr 26, 2008)

rstolz said:


> check your fuel trim.
> 
> s.


Would the fuel trim have changed on its own somehow?


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## diamono (Apr 26, 2008)

*Update - Sometimes Works - EPC Light Question*

Found some vacuum leaks, but nothing major. Sometimes the engine runs fine with the MAF plugged, but most of the time it won't. Last night after checking and re-checking stuff, I called it a night after starting the car 3 or four times with the MAF plugged in and the engine running like it should. When it's running like it should, measuring block 033 (short term fuel trim) runs around +/- 4% most of the time, but will sometimes go up to 20, so I am assuming there are still some leaks somewhere. Scanning through with VCDS, I did find an odd code on the transmission for 00529 (Engine speed signal missing - intermittent).

Driving the car to work today, all was well until I got onto the interstate. After about a mile, the car started bucking when the throttle was held steady. For about 10 miles, I would give it some gas and let off, repeating the process to keep it going. Every now and then it would smooth out for awhile, but the problem would return. I figured when I got off at my exit that I would unplug the MAF. However, before I got off, it smoothed out again and stayed smooth another 5 miles until I got to work.

What I noticed from the dash, was that my EPC light was coming on and going off. Whenever the engine was running properly, the light would be off. If it was having problems and I was holding the throttle steady (car bucking), the light would come on. If I was pushing the pedal down, it would be on. When I would let off the gas, the light would go off.

I may have something loose somewhere, but so far, I've tried wiggling and pulling on every wire I can get my hands on, but cannot change the state of the engine running when it's doing fine.


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## diamono (Apr 26, 2008)

Possibly some progress. When car won't run with MAF plugged in, I checked for power on blue/yellow wire MAF and had none with ignition on. Searched all over and found a thread in the New Beetle forums that power for MAF was coming from fuse 43 for engine control. When I pull fuse 43 and check for power with my multimeter, I only read 1.2V. With the fuse removed, I also read 1.2V at the the MAF. Interestingly enough, the car will start and run fine with this fuse removed. While running, I can plug this fuse in and see the voltage meter go to 14.4 at the MAF. There is a slight engine stutter as it adjusts, but will run fine. However, the car may or may not continue running. If it ever dies, MAF voltage shows 0. The car so far always starts with the fuse removed, but sometimes dies when plugged in. Whenever the car runs without the fuse plugged in, I get the following fault codes showing up in VCDS:

VCDS-Lite Version: Release 1.2
Saturday, 28 March 2015, 11:15:59:6238
Control Module Part Number: 06A 906 032 B
Component and/or Version: 19MATA31.HEX 230G 2846
Software Coding: 10143
Work Shop Code: WSC 00066
VCID: 1D4D422984A9
8 Faults Found:
17833 - EVAP Purge Valve (N80): Short to Ground
P1425 - 35-00 - -
17525 - Oxygen (Lambda) Sensor Heating Circuit: B1 S2: Short to Ground
P1117 - 35-00 - -
17843 - Secondary Air Pump Relay (J299): Short to Ground
P1435 - 35-00 - -
17829 - Secondary Air Injection Solenoid Valve (N112): Short to Ground
P1421 - 35-00 - -
17606 - Oxygen (Lambda) Sensor Heater Circuit: B1 S2: Electrical Malfunction
P1198 - 35-00 - -
17880 - EVAP Leak Detection Pump: Short to Ground
P1472 - 35-00 - -
16486 - Mass Air Flow Sensor (G70): Signal too Low
P0102 - 35-00 - -
17523 - Oxygen (Lambda) Sensor Heating: B1 S1: Short to Ground
P1115 - 35-00 - -

I do not get these fault codes running without the MAF Plugged in. I only get these codes running it without the fuse #43 plugged in.

Is there a relay somewhere that is providing power to fuse 43? I'm trying to understand why I only read 1.2V with the fuse unplugged, and yet when plugged in, I'll get 14.4V showing at the MAF when running.


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## diamono (Apr 26, 2008)

Oh well, this is all the ravings of a mad man. Still no progress. Having the fuse out appears to do the same thing as unplugging the MAF.Still no clue as to why this issue is intermittent.


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## ticketed2much (Feb 18, 2012)

Read in some other posts multiple short to ground could be fuel pump relay/fuse, corroded grounds(probably not), or bad cam chain tensioner sensor.


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## diamono (Apr 26, 2008)

ticketed2much said:


> Read in some other posts multiple short to ground could be fuel pump relay/fuse, corroded grounds(probably not), or bad cam chain tensioner sensor.


I'll definitely look at those, although if I had a short to ground or an issue with a hard part, I would think it would show up when the MAF was unplugged too. Any idea of what to search for to find out what items (sensors, etc.) are used when the MAF is plugged in and when it's not? After a clearing of codes and driving a couple of days, I never have anything show up for the engine other than the MAF signal.


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## diamono (Apr 26, 2008)

ticketed2much said:


> Read in some other posts multiple short to ground could be fuel pump relay/fuse, corroded grounds(probably not), or bad cam chain tensioner sensor.


In "bad cam chain tensioner sensor", is that referring to the cam sensor that is partially under the timing belt cover at the top, or something else? I've tried another cam sensor there and it didn't affect anything. The only oddity that I have found right now, is that I measure 5V across the left and right plug wires that go to the sensor when there is no key in the ignition. On a Jetta I have, I do not have any power going across those wires until the ignition is turned on.

The other thing that is odd, is that when I pull a fuse, say those around #43, I have around 2 volts measured from the left terminal to ground and have 12 volts from the right terminal to ground (some of them have to have the ignition on for the 12V reading). Could be some short somewhere causing this, but don't know where else to look for this to narrow it down. Also wondering if a relay somewhere could be causing this condition. Lastly, on a scan of the Central Conv, I get 01329 - Convenience System Data Bus in Emergency Mode. Could that possibly be related. I haven't been able to narrow that one down either as everything seems to function as it should.


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## Jadiel18 (Dec 16, 2012)

My buddy had an O2 sensor that melted on the Cat shorting out and causing the fuse #43 to pop.

the car idled badly and he got all those codes you listed. I Fixed the O2 and replaced the #43. got everything up and running like normal.

hope this gives you some ideas, hope you get this sorted out :thumbup:


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## diamono (Apr 26, 2008)

O2 sensors and wiring appears good (at least around the CAT area and connectors). Boy, this sure is fun.


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## rstolz (Jun 16, 2009)

> code on the transmission for 00529 (Engine speed signal missing - intermittent)


This is triggered by the crank sensor. Normally I don't promote throwing parts at cars without knowing things for certain, but in this case, those sensors are finnicky, and cause lots of odd symptoms.

Change your crank sensor. It's one bolt, down near the oil filter. easy to do, hard to reach, and if you shop around the sensor is cheap.

beyond that you have a short in your emissions control circuit somewhere. All of the items on that scan are fed by the same 2 sources. In the box where the main power relay sits under the hood, there is a second large relay, that one is for the emissions controls. That relay likely isn't your problem, I'm just saying that the each one of those codes has power flowing through that relay; except for the 02 sensor and MAF, those flow through the other relay. they are tied to emissions controls, but primary function is A/F control, which is on a different circuit

It actually looks like you've done an SAI delete or bypassed the N249.


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## diamono (Apr 26, 2008)

First off, let me say that my prior post showing codes may be a bit misleading. These are codes that show up *only* if pull the #43 codes and drive. These codes *do not* show up if I drive with the MAF unplugged. The only code that shows up is for the MAF

16486 - Mass Air Flow Sensor (G70): Signal too Low
P0102 - 35-00 - -


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## diamono (Apr 26, 2008)

Last night, I tried swapping the crank sensor with a spare. Engine runs as it should. I get off the ramps, head up the drive way and it dies. Won't run. Unplug the MAF, head home and get back up on the ramps and swap the crank sensor back to original.

Next step, pull the DV off and check it, clean the PCV(?) valve and get some junk out of the hose going to it. Put it all back together and the engine starts and runs as it should. Get off the ramps and head up the driveway. Drive down the road, turn around to come home and it dies. Won't start. Unplug the MAF, head home and get back up on the ramps. Thinking maybe it was the crank sensor after all. Swap out the crank sensor again with the spare. Try starting and it won't run.

I've tried tracing every wire under the hood that I can. I've gently traced, tugged and pulled on all the wires under the hood from the top and most under the engine and can't seem to find a bad connection anywhere. I may be wrong, but my gut is telling me, I either have a short or a break that causes mis-reads of the ECU and creates the condition where the MAF plugged up won't run.

One other item of note, when it won't run right. If I have my MAF housing separated from the intake (no air flow through it), I can run the car with MAF plugged up. In this condition VCDS will show 0.0 g/s due to no air flow. As soon as I take the MAF housing close to the intake and it gets some air flow through it, it'll die. Reminder too, that I've tried two other known good MAF's (I've got five VW's at my house) and they don't make any difference.


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## rstolz (Jun 16, 2009)

diamono said:


> One other item of note, when it won't run right. If I have my MAF housing separated from the intake (no air flow through it), I can run the car with MAF plugged up. In this condition VCDS will show 0.0 g/s due to no air flow. As soon as I take the MAF housing close to the intake and it gets some air flow through it, it'll die. Reminder too, that I've tried two other known good MAF's (I've got five VW's at my house) and they don't make any difference.


that's not surprising, leaving the MAF hanging loose with no flow is the same as unplugging it. Your car is running in open loop.

pull all 4 spark plugs, take a close picture and post them here. We can tell if you're running rich, lean or ideal from that, amongst other things.

Have you tested the fuel pump? WHen the car is running in open loop, it runs an enriched fuel mix, so it can mask a bad fuel pump. You would want to do a flow AND pressure test.

I'm still concerned about the engine speed signal, but it doesn't sound like that's your primary issue. To that end, have you ever encountered hard starts or what appears to be RPM hangs and loss of throttle response at specific RPM?


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## diamono (Apr 26, 2008)

Thanks. I have a fuel pressure gauge and will see if I can find out where to hook it up. I'll also check the spark plugs (I know I probably should have checked that first, that's so old school and I guess I've just gotten too dependent upon VCDS to show me what to look for. lol). Along those same lines, I'll see if I can check the fuel filter, power supply, relay, etc., dealing with that portion of the system. Hopefully, I can get to it this evening. I was discounting that part of the system due to running ok without the MAF. I guess I need to learn more more about what all system the MAF uses and doesn't use...


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## rstolz (Jun 16, 2009)

You learn that crap by having issues and figuring em out, most of us hanging around here were in your shoes at one point or another. If they disagree they're lying or do this professionally.


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## diamono (Apr 26, 2008)

Two shots of the spark plugs. A lot of crud. Not sure if it's from running without the MAF plugged up, which has been about 250 miles of off an off driving over 10 days, or if they were already that way.


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## diamono (Apr 26, 2008)

Concerning fuel pressure, I did do some checks, but they probably weren't accurate. I didn't have a proper T, so the first check was just connecting the pressure gauge directly to the line going back to the tank. At this point I had 90 lbs. I don't know if there is anything to it or not, but despite the issue with the MAF, the car did idle with it hooked up, but not really smooth. The second check was by putting a cobbled together T in line with the line coming from the pump to the manifold. I got a reading of 40 lbs., but it was leaking too much fuel at the T, so I didn't let it run very long. I don't know what I would have gotten if I had a T that didn't leak.


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## noggin88 (Mar 6, 2017)

*Engine Dies as soon as MAF is plugged in*

I see this post is from 2 years ago.

did you ever find the solution to your MAF issue? 

I have the same issue, except the car will not run at all with the man plugged in.:banghead:

very curious if you had found a solution since then 

cheers


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## Mr muss (Dec 29, 2020)

You fondo out your maf circuito?


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