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1998 Subaru Forester mystery stalling

We have a '98 Forester S 2L (not the 2.2L) with 169,000 miles. It’s been extremely reliable, but recently it’s started stalling a lot. It starts up fine, we start driving, and then suddenly there’s a severe loss of power and stalling (while driving or while stopped). We know that it’s not the ignition module, and we’ve had the spark coil replaced. It seems to have something to do with the fuel-air ratio (the air meter reading is impossibly high), but we haven’t been able to locate the source of the problem. It also seems worse after driving, turning it off for a few minutes (i.e., stopping for gas), and then starting again.

Is the Check Engine Light on? If so, have you had the computer scanned for diagnostic codes? What are the codes?

Thanks for responding. The computer was scanned, and the only code that came up was for the ignition module, so we had that replaced - but it didn’t fix the problem or even lessen it. However, the Check Engine light has not come back on.

Please explain “the air meter reading is impossibly high.”

How old is the fuel filter?

Of course the car has no air meter - but the mechanic’s diagnostic computer read 60 cfm. I have no idea how old the fuel filter is (we’ve never had it changed), but apparently it’s working fine. Is there something usual we should be looking for? By the way, my husband is an aircraft mechanic and our car mechanic is someone who knows Subarus. We also have a '93 Legacy wagon.

If you have no idea of how old the fuel filter is, that means that you need to change it now. The schedule for this maintenance is every 3 years/30k miles (whichever comes first). Fuel filters are much cheaper than fuel pumps, and an old partially-clogged fuel filter will effectively shorten the life of your fuel pump.

Thanks for the suggestion. The fuel pump doesn’t seem to be even partially clogged, but since it’s old it may be much less efficient than it should be. We’ll do that, and let you know what happens!

If changing the fuel filter doesn’t correct the trouble I would look into something possibly going on with the MAF sensor.

Thank you both for your suggestions. The MAF sensor has been checked. Still waiting to hear back from the mechanic, but we’ve narrowed it down to either the fuel filter or the crank case breather & pcv valve.

That is interesting. I will be surprised if that really is the trouble here. It would be any easy fix if it is.

Hi, there.

I’m not particularly knowledgeable about cars, but I also have a 1998 Subaru Forester and encountered a similar problem this summer. My mechanic replaced my mass air flow meter, and it did the trick. It wasn’t a cheap fix - he replaced it with a new part and it was still in the ballpark of $700 - but it did the trick. So, that’s another option you might consider. My car stalled a few times, and I thought little of it and kept driving and within a few weeks, the problem got bad enough that it would hardly start or drive at all.

Hmmm… I sure hope it’s not that, since we don’t have that kind of money right now, but I really appreciate your comment. The mechanic said that he check the MAF sensor - but then again, he also replaced a couple of things that ended up having nothing to do with the problem at all.

Since you’ve never changed the fuel filter I would suspect this little oversight is killing the fuel pump.

It’s quite possible, and very often the case, that an engine can run perfectly fine with a clogged filter. The unseen damage is that the pump is having to work harder and the pump life is shortened.
And a pump can be a come and go thing like this.

Filters should be changed about every 15k miles and even more often if any contamination is suspected.

Couple of examples.
I change my fuel filters every 15k miles and about 2 years ago just before taking an out of state trip I pulled the filter off of my Lincoln (12k miles on it) and it was plugged up solid. I changed the filter and made the comment to my wife half a dozen times I hoped the pump was not harmed.
So after a 1500 miles trip and about 20 miles from the house at night during a driving thunderstorm the fuel pump died on me.

My daughter in law and son were visiting and while doing maintenace on their car I discovered that the fuel filter on her Lincoln was also clogged, and apparently not changed by the lube facility they were using in another state. (original Ford filter still on it)
I told them they may have pump trouble in the future and about 6 months later while coming back to OK to visit the pump died on them in western KS; leading to a tow and spending the night in a motel.

I’ve also seen near new cars towed in due to clogged filters and these cars had less than 2k miles on them. One had a measly 400 miles on it.

I’d recommend pulling the filter off, draining it, and allowing it to sit for a couple of hours to dry out.
Try blowing through it. If you can blow easily through it (not likely) the filter is good. If it takes a little, or a lot, of effort then the filter is bad and the pump is likely right behind it.

Changing the fuel filter is certainly a very good thing to do and hopefully that will fix it. If that doesn’t work you may want to try cleaning the MAF sensor next. Maybe it is just dirty.

The fuel filter is clear, and the MAF sensor was cleaned. It seemed to improve slightly, but that didn’t last. Now the mechanic has found that 5 sensors are all losing voltage for a few hundredths of a second whenever the stalling occurs. We are now looking for what could cause a multiple loss of sensor voltage. I personally suspect the ignition relay - next to be checked. Will keep you posted…