Driving without MAF sensor?
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  1. #1
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    Driving without MAF sensor?

    I've had P1127 & P1138 error codes for a while. A few days ago, my car drove like total crap with misfires in all 4 cylinders. I scanned again and the P300, P301, P302 & P303.

    I ran a course of Techron to clean the injectors and that didn't help. Driving home last night was CRAZY. It would misfire at any slight acceleration.

    Well, I disconnected the MAF sensor this morning, and boy, did she drive smooth - not even a misfire or jerk. I ordered a new MAF sensor, but won't have it over till a couple of days.

    How safe is it to drive with the MAF sensor disconnected?

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  3. #2
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    bump

  4. #3
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    You can be fine indefintely, but you'll have to get used to a CEL and you won't know if there's a second code for the CEL either. May just run a tad richer in some driving conditions and overall mpg may drop a few. Fuel trims should level it out for the most part.

  5. #4
    (insert title) Moderator Steve in Chicago's Avatar
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    Quote Originally Posted by ddgbosi View Post
    How safe is it to drive with the MAF sensor disconnected?
    Well, in your particular case, it's probably better for your engine if you do drive with the MAF disconnected. Your ECM "guessing" how much fuel to provide is more accurate than your ECM calculating off the bad data provided by your faulty MAF (that's why it's running better this way).

    When you get the new MAF installed, it should run even better.

  6. #5
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    If you have a auto you might get a really brutal 4-5 upshift with the Maf disconnected. My car ran great with the Maf disconnected. But the 4-5 upshift was so brutal I had to pull over and connect it again.

  7. #6
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    Well, got a remanufactured MAF from AutoZone for $55. Car runs smooth, it's unbelievable. This would be the 4th I've replaced in the last 2.5 years.

    By the way, I changed my air filter last week, and today when I go to change the MAF, it looks like it's being soaked with some mixture of oil from somewhere. Any ideas?




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    Space for rent
    Last edited by ddgbosi; 11-13-2009 at 02:00 PM. Reason: Duplicate post

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    thats weird.

    is there oil on the inside of the intake tubing?

  10. #9
    (insert title) Moderator Steve in Chicago's Avatar
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    That stain does not look normal. I run a 4" COAM from my lower grill up to a 3" reducer that enters the bottom corner of my airbox and I've driven in heavy rain and not had my filter liquid-stained like that. Is your intake path stock?

    I wonder if that's why you're going through MAF's at the rate you are. Could it be that the MAF sensor is becoming dirty/contaminated with the oil and dieing? Have you ever tried cleaning the MAF sensor with MAF sensor spray cleaner?

    I'd pull things apart and start examining really closely to see where that oil is coming from. It's bound to be leaving oil traces along it's path of travel.

  11. #10
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    Hockey puck valve?

  12. #11
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    Quote Originally Posted by jhorkey View Post
    Hockey puck valve?
    It's full.

    Carefully disconnect it and dump it.

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    Quote Originally Posted by jhorkey View Post
    Hockey puck valve?
    Quote Originally Posted by ONE8T View Post
    It's full.

    Carefully disconnect it and dump it.
    What and where? By the way, 3 years, 4 MAF's and 80K miles later, my check engine light finally went off.

    I didn't even reset this time

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    The puck valve is downstream from the filter. I fail to see how it could overcome gravity and send oily residue UP and thru the maf, then onto the filter.

    Are you sure there are no problems with your SAIP? The stain looks to be on that side of the box. would also stand to make sure the coimbi valve is working too.

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    Quote Originally Posted by VAGguy View Post
    The puck valve is downstream from the filter. I fail to see how it could overcome gravity and send oily residue UP and thru the maf, then onto the filter.

    Are you sure there are no problems with your SAIP? The stain looks to be on that side of the box. would also stand to make sure the coimbi valve is working too.
    Had SAIP issues in the past. Indy said it was not working at all, but I got home and found out it was disconnected, and the fuse was out. I connected it and replaced the fuse, and it seems to be working fine - at least I hear it come on when I turn the car on for a cold start.

    I doubt it is the puck valve, as I did a complete PCV replacement not too long ago (well, sort of long ago; ~1 yr)

    Maybe the SAIP is really out, then.

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    (insert title) Moderator Steve in Chicago's Avatar
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    If the SAIP isn't connected, that should throw a code and light the CEL. The filter stain looks like it may be coming from where the SAIP air intake connects to the filter box. I wonder if this is why the PO disconnected it. Perhaps he decided it was better to live with a SAIP CEL then to keep buying MAF's?

    If the SAIP system is working properly, it draws air in from that port on the air box and pumps it to the combi valve. It shouldn't be backflowing anything up into the filter box. Problem with the combi valve?

    If you get under the front of the car you can disconnect the two hoses from the SAIP. (1. from air box to SAIP, 2. from SAIP to combi valve)They clip on and if you push on the tabs just right, they will clip off. See if they are filled with liquid. They should be relatively clean and dry inside.

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    Quote Originally Posted by Steve in Chicago View Post
    If the SAIP isn't connected, that should throw a code and light the CEL. The filter stain looks like it may be coming from where the SAIP air intake connects to the filter box. I wonder if this is why the PO disconnected it. Perhaps he decided it was better to live with a SAIP CEL then to keep buying MAF's?

    If the SAIP system is working properly, it draws air in from that port on the air box and pumps it to the combi valve. It shouldn't be backflowing anything up into the filter box. Problem with the combi valve?

    If you get under the front of the car you can disconnect the two hoses from the SAIP. (1. from air box to SAIP, 2. from SAIP to combi valve)They clip on and if you push on the tabs just right, they will clip off. See if they are filled with liquid. They should be relatively clean and dry inside.
    Will do. When I connected the SAIP and replaced the fuse, it drained out some really dark liquid - it was so dark it left stains on my driveway. Just thought I'd mention. I think I'd look for a cheap SAIP from local junkyards

  18. #17
    (insert title) Moderator Steve in Chicago's Avatar
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    Quote Originally Posted by ddgbosi View Post
    When I connected the SAIP and replaced the fuse, it drained out some really dark liquid - it was so dark it left stains on my driveway.
    Probably a bad combi valve. One of the things a bad combi can do is allow moisture (not sure where it originates. exhaust condensate?) into the pump. This kills the pump after a while. The dead pump triggers a SAIP related CEL and the owner will replace the pump to get things working again. A short while later the new pump will die for the same reasons and need replacement. This will go on and on till someone figures out why the car goes through SAIP pumps like crazy and address's the combi valve.

    Do some searches. I know someone here has gone down that path before.

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    Quote Originally Posted by Steve in Chicago View Post
    Probably a bad combi valve. One of the things a bad combi can do is allow moisture (not sure where it originates. exhaust condensate?) into the pump. This kills the pump after a while. The dead pump triggers a SAIP related CEL and the owner will replace the pump to get things working again. A short while later the new pump will die for the same reasons and need replacement. This will go on and on till someone figures out why the car goes through SAIP pumps like crazy and address's the combi valve.

    Do some searches. I know someone here has gone down that path before.
    If I'm not mistaken, indy said he needed to replace the SAIP and the solenoid. Can a VAG-COM scan tell me exactly what's broken, if any?

    If the SAIP or combi valve was broken, shouldn't I have a check engine CEL?

  20. #19
    (insert title) Moderator Steve in Chicago's Avatar
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    Quote Originally Posted by ddgbosi View Post
    Had SAIP issues in the past. Indy said it was not working at all, but I got home and found out it was disconnected, and the fuse was out. I connected it and replaced the fuse, and it seems to be working fine - at least I hear it come on when I turn the car on for a cold start.
    Quote Originally Posted by ddgbosi View Post
    If I'm not mistaken, indy said he needed to replace the SAIP and the solenoid. Can a VAG-COM scan tell me exactly what's broken, if any?

    If the SAIP or combi valve was broken, shouldn't I have a check engine CEL?
    Did he unplug it in order to make you think you need a new one? Does he not know the fuse and relay for it are in the ECM box? Did he read the codes and is simply throwing parts at the car without any testing? Just sounds odd. Ask him to explain his diagnosis.

    If the SAIP is not running at the proper times, it should throw a code. If it's running but the hose from pump to combi is blocked or split, it should throw a code. If the combi valve is not working properly, it may or may not throw a code.

    A lot of times reading the codes isn't as simple as it telling you exactly what part to replace. The codes need to be interpreted. The more familiar you are with the way the car works, the more accurate your interpretation will be. Your mechanic may be the best general mechanic in the area, but if he's not familiar with the particulars of the SAIP & Combi as they are implemented on these cars, he's likely to mis-diagnose and end up throwing parts till the actual problem is found.

    Look up on-line and in the Bentley Manual the procedure for testing the combi valve and the SAIP. Perform those tests. Or dig up the testing procedures for your mechanic and let him perform them.

    ESC lists SAIP's for $300-$400 and combi valves for $160-$200.
    A bad combi can kill a SAIP. And in your case, it may also be killing MAF's.
    If you don't find the root of the problem, this could get really expensive over time.

  21. #20
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    Quote Originally Posted by Steve in Chicago View Post
    If the SAIP isn't connected, that should throw a code and light the CEL. The filter stain looks like it may be coming from where the SAIP air intake connects to the filter box. I wonder if this is why the PO disconnected it. Perhaps he decided it was better to live with a SAIP CEL then to keep buying MAF's?

    If the SAIP system is working properly, it draws air in from that port on the air box and pumps it to the combi valve. It shouldn't be backflowing anything up into the filter box. Problem with the combi valve?

    If you get under the front of the car you can disconnect the two hoses from the SAIP. (1. from air box to SAIP, 2. from SAIP to combi valve)They clip on and if you push on the tabs just right, they will clip off. See if they are filled with liquid. They should be relatively clean and dry inside.
    I think there's a better chance vacuum when off boost is drawing moisture out of the full puck and back through the TIP to the box than any moisture coming from the line that feeds the SAIP. It's all part of that system though. The stain extends as much to the TIP area than the SAIP feed.

  22. #21
    (insert title) Moderator Steve in Chicago's Avatar
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    Quote Originally Posted by ONE8T View Post
    I think there's a better chance vacuum when off boost is drawing moisture out of the full puck and back through the TIP to the box
    That would require the moisture to travel upstream (against the airflow) from the puck located in the TIP, through the MAF and onto the filter.

    Anything coming out of the puck would get sucked along with the airflow (through the TIP and into the turbo).

  23. #22
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    Quote Originally Posted by Steve in Chicago View Post
    Did he unplug it in order to make you think you need a new one? Does he not know the fuse and relay for it are in the ECM box? Did he read the codes and is simply throwing parts at the car without any testing? Just sounds odd. Ask him to explain his diagnosis.

    If the SAIP is not running at the proper times, it should throw a code. If it's running but the hose from pump to combi is blocked or split, it should throw a code. If the combi valve is not working properly, it may or may not throw a code.

    A lot of times reading the codes isn't as simple as it telling you exactly what part to replace. The codes need to be interpreted. The more familiar you are with the way the car works, the more accurate your interpretation will be. Your mechanic may be the best general mechanic in the area, but if he's not familiar with the particulars of the SAIP & Combi as they are implemented on these cars, he's likely to mis-diagnose and end up throwing parts till the actual problem is found.

    Look up on-line and in the Bentley Manual the procedure for testing the combi valve and the SAIP. Perform those tests. Or dig up the testing procedures for your mechanic and let him perform them.

    ESC lists SAIP's for $300-$400 and combi valves for $160-$200.
    A bad combi can kill a SAIP. And in your case, it may also be killing MAF's.
    If you don't find the root of the problem, this could get really expensive over time.
    I'd look into it over the weekend. Thanks for your help.

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