Intermittantly sputtering Legacy

[Mikevan10]

OK. I’m back!

 

I’ll try to keep the story short. Basically, after we last spoke, I went ahead and drove the car to Jones Beach and back. No problem whatsoever. Wife continued to use car on a regular basis. Put over 800 miles on it after changing out the fuel filter with no problem and no MIL. Then one day while I was driving the car it started sputtering about ½ mile from home. MIL came on by the time I rolled into my driveway. Borrowed an OBDII scanner and code P0102 “MAF sensor low input” was up. Let car sit overnight. Started it up and it ran fine. I cleared the code. Drove the car on a 15 mile run. No problem. The car sat for about 5 hours. Attempted to drive home and within 2 or 3 minutes of starting the engine and 1 mile of travel, it began sputtering and the MIL illuminated. I managed to nurse it all the way home (which included climbing over a nice steep ridge-never thought it would make it). It was a hellish ride in the wee hours of the morning… Ignored the car for a couple days. Scanned OBDII. P0102, of course. Cleared the code. Started the engine. Ran fine. Drove a couple of miles. No problem, no MIL. Decided to clean the MAF sensor with the CRC MAF sensor cleaner spray. Also used the same spray to clean the connector plug. Waited about 15 minutes then started the engine. Sputtering badly! MIL illuminates. Code is P0102. I let the engine run/sputter while I jiggled the MAF sensor connector and associated wires until they disappear into the wiring harness. No change. Shut the engine down. Restarted. Still sputtering. Threw in the towel for the night.

 

I have a Subaru factory manual but, in the Troubleshooting section it does not list P0102! It only includes P0100 and P0101. I have not studied those procedures yet but I plan to see if they help.

 

Anyone have a specific procedure for P0102 or any other suggestions?

 

Thanks as always,

 

Mike V.

[unibrook]

don't know if this will help, but when my 2001 Forester (83k) was bucking/coughing intermittently it turned out to be the front o2 sensor needed replacement. I NEVER got a code for the front o2 sensor. Instead, I kept getting PO302 and PO304 misfire codes.

[wtdash]

Time for a new/different MAF?...got any junkyards nearby?

 

Good luck.

[Mikevan10]

Just thought I’d check in again, to BUMP this thread back up, if nothing else.

 

In the mean time, I tried to check out the MAF sensor circuit wiring and function. This was a bit tricky since, as I mentioned above, my circuit does NOT match the one shown in my Subaru factory manual. Anyway, I measured 1.4 ohms between the ground pin on my MAF sensor plug and the engine block (i.e. ground). I measured 1.6 ohms between the ECM and the MAF sensor. I get full battery voltage (like 12.6 volts) at the power input pin on the MAF sensor as soon as I turn the ignition switch on. With everything hooked up, I “back pinned” the EDCM connector plug so I could monitor the MAF sensor output voltage. With engine off it read 0 volts (of course). With the engine idling it was about 1.0 volts. When I revved the engine the voltage would increase proportionately. I saw about 2.5 volts when I would give it a good goose. Of course, while I was doing this testing, the engine was running fine. As I have said, this is a very intermittent problem – most of the time, the engine runs fine, then, for no apparent reason, it will suddenly start sputtering/misfiring badly. And it does not seem to correlate to engine temperature, ambient conditions or anything else. Also, the MIL does not always illuminate, even with it sputtering something bad. Other times the MIL comes right on and the code is P0102.

 

I guess I should just replace the MAF sensor and see if that fixes it. I really hate to do so without KNOWING that that is the culprit. New ones cost about 300 bucks so it will have to be a used one. Not sure how much I’ll have to pay but it aint gonna be a 10 dollar item… I don’t understand how what seems to be a fancy resistor could have an intermittent failure. Do you? Isn’t there a direct test of the darn thing?

 

Also, as I mentioned above, my official Subaru manual does not have a trouble shooting routine for P0102 nor does the wiring diagram exactly match my car. Any help on either of these?

 

Driving the 25 year old, 300,000 mile VW van to Maine this weekend because the Subaru is not reliable.

 

Mike V.

[McDave]

You're fortunate to have that trouble code. I've had to gamble on more expensive mafs with even less to go on. Go for it.

[OB99W]

[...]Anyway, I measured 1.4 ohms between the ground pin on my MAF sensor plug and the engine block (i.e. ground). I measured 1.6 ohms between the ECM and the MAF sensor.[...]

Assuming you "zeroed out" the meter lead resistance, those readings seem a bit high -- I'd expect them to be under 1.0 ohm.

 

 

As I have said, this is a very intermittent problem – most of the time, the engine runs fine, then, for no apparent reason, it will suddenly start sputtering/misfiring badly. And it does not seem to correlate to engine temperature, ambient conditions or anything else.

I wonder if the cause could be a failing contact on the main relay. The MAF is one of a few things fed by it, but it may be the one that the ECU is particularly sensitive to.

 

 

Also, the MIL does not always illuminate, even with it sputtering something bad. Other times the MIL comes right on and the code is P0102.

The P0102 MAF code causes the MIL to light immediately, while other problems that can cause "sputtering" might require a restart before it's lit.

 

While the MAF itself certainly could be intermittent, you might try rapping on the main relay and see if engine running condition and/or MAF voltage changes when you do.

[Mikevan10]

Replaced MAF sensor yesterday. Car ran "fine" for about 10 miles and then began sputtering again.

 

Does anyone know how I can fim=ne the ground connection in the MAF sensor circuit. Maybe tghe ground connection is shaky.

 

Grasping at straws. A bit desperate. Very poor.

 

Mike V.

[OB99W]

Mike, did you try what I suggested in the last sentence of post #31, concerning the main relay?

[Mikevan10]

Not yet, OB. But I will try that tonight. If I recall correctly, the Main Relay is located in the pasenger compartment, under the dah to the left of the sterring column, right?

 

I just got back to work after "rescuing" my wife with the broke down Legacy. It had stalled and would not start. Actually, when I tried to start it, it would make a half hearted attemt to run but would stall immediately. I disconnected the MAF sensor and the car started up, although it ran roughly. This tends to make me wonder about the condition of the used MAF sensor that I installed last night. Of course the guy at the independent Subaru repair/used car/used parts shop told me he was sure it was good...

 

Thanks for the thoughts!

 

Mike V.

[McDave]

I would go back to the junk yard and tell him the one you bought failed after 10 minutes and you would like to exchange it. That shouldn't be a problem if he has another one.

 

In the meantime, if you can get the car to act up again, try disconnecting the front O2 sensor and see if it straightens out.

[OB99W]

Not yet, OB. But I will try that tonight. If I recall correctly, the Main Relay is located in the pasenger compartment, under the dah to the left of the sterring column, right?

That should be the location, and it's typically square and brown in color. You should probably still try tapping on it to see if running conditions change, but I'm less inclined to consider it given the additional info you've since provided.

 

 

[...]This tends to make me wonder about the condition of the used MAF sensor that I installed last night. Of course the guy at the independent Subaru repair/used car/used parts shop told me he was sure it was good...[...]

Often if the engine runs better without the MAF connected than with it, the MAF itself has problems. As McDave suggested, if another MAF is available, it could be worth trying. Then again, both MAFs may be good and the problem due to poor connections or otherwise.

 

You had previously mentioned that the car ran "fine" for about 10 miles with the used MAF, but until things are warmed and the ECU isn't running open-loop, that period isn't very telling. As has been already mentioned, if the front O2 sensor is disconnected, that will also cause the ECU to go to default settings, since it will look like the sensor hasn't warmed up.

 

Mike, please check your Private Mail.

[McDave]

As has been already mentioned, if the front O2 sensor is disconnected, that will also cause the ECU to go to default settings, since it will look like the sensor hasn't warmed up.

I've also seen O2 sensors short out intermittently and cause the engine to run so bad I was sure it needed a coil. I was reminded of this yesterday when a Dodge truck came in with an occasional miss and no CEL. While test driving it with the scanner monitoring for misfires, it started missing so bad I didn't think it would make it back to the shop. Oddly no misses were showing on the scanner. Fortunately it finally set a code for a shorted O2 sensor and I checked and saw the O2 voltage zero-ed out. Problem solved!

 

I was also reminded that misfires can set codes that aren't directly related to the problem. A misfiring Chevy Vortec V8 is prone to set a MAF code just from the disruption of airflow, when the real problem is ignition related. With that in mind, I'm now less inclined to believe that you have a MAF problem, Mike.

 

It would still be worthwhile to try another MAF if you can get one free, but then I would start looking in other directions, like an O2 sensor shorting out. Unplug it when the car is acting up to see how it runs.

 

Edit: It would also be worthwhile to check the maf voltages and ground while it's acting up, if possible, before ruling out the maf. Check for ground the same way you checked running voltage, by backprobing the connector.

[Mikevan10]

Seems like I have y‘all stumped. Well, here’s some more clues in case it shakes something loose:

 

First off, for the “troubleshooting” I was doing last night, the car cooperated in that it sputtered consistently. What I mean is that although the trouble has been intermittent, it stayed with me throughout my test session. The engine will start and idle, but it is VERY rough. And it is very difficult to coax it to rev up. Tends to stall.

 

I disconnected the front oxygen sensor. This made no difference whatsoever. I disconnected before starting the engine and it made no difference. I also disconnected it WHILE the engine was running and there was no change in the (lousy) running condition.

 

With everything connected and the engine idling (very roughly), if I disconnect the MAF sensor, the idle immediately smoothes out, the revs pick up a little (probably to normal idle speed) and then the engine stalls. This all takes place within about 5 seconds.

 

With the MAF sensor disconnected, the engine starts right up and idles smoothly. However, if I try to rev it up it misfires/stumbles. It does not stall and I can get it to rev as high as I want (though it is rough). If I plug the MAF sensor in while it is running the engine stalls immediately.

 

Spanking the Main Relay (brown cube) has no effect on the running conditions. I also back pinned the power feed wire at the MAF sensor connector plug and monitored the voltage there and the voltage was rock steady while spanking the relay.

 

I plan to visit the shop that sold me this MAF sensor on my way home from work tonight and see what they say. Like I said, they specialize in Subarus.

 

Any more ideas?

 

Thanks guys.

 

Mike V.

[McDave]

 

Any more ideas?

 

Thanks guys.

 

Mike V.

Yes, try disconnecting the tps the next time it acts up.

 

I understand funds are tight, but you might consider springing for a proper diagnostic scan, one that can read and store the data in movie mode while it's acting up. Then if the problem isn't obvious at the moment, it can be downloaded and studied later. Our shop charges 1.5 hrs for this and includes the labor to replace something simple like an O2 sensor or maf.

[McDave]

I just thought of something else. It sounds like once this new maf acted up it stayed messed up. Clean it with your cleaner and try again. If it's still messed up, put your old one back in.

[Mikevan10]

I neglected to mention that i did clean the MAF sensor (with CRC MAF sensor cleaner) last night. Made zero difference.

 

"It sounds like once this new maf acted up it stayed messed up."

 

Actually, after stranding my wife yesterday, I was able to collect the car and bring it home. It was acting up when I first started it but it then pretty much smoothed out and I was able to drive it home (about 6 miles). It ran ok until I was just about home, then began sputtering, then stalled and I coasted into my driveway.

 

Always grateful,

Mike

[Mikevan10]

Quick update:

 

I got another used MAF sensor from the Subaru repair/salvage shop. It has been in the car for about 130 miles so far without any problems. So far so good, but this problem was intermittant and I have gone over 300 miles between occurences of trouble before (on the original sensor). Will take a while before I will assume that it is fixed.

 

Mike

[korrupt66]

I've got this same problem with my 97 leg wagon 2.2 Looks like its safe to say you needed a new maf.