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Hi All,
Car in question is a 2.5L 98 outback.
Been meaning to post up a thread on what i've done to improve the fuel economy (and the reading on the fuel gauge).....
Anyway, since I've had the car, I've run the 'upper engine cleaner' through it, some injector cleaner, and of course, oil, oil filter, spark plugs.
It seems to have a fairly consistent 'minor' surge. I do a lot of highway driving, and I'll have the cruise control on, sittling at about 100-110 (depending on speed limit), and I experience small 'surging'. It also does it at almost any spped/RPM. More of a slight, intermittant loss of power that any thing else. Actually, it's more like a 'lugging' sensation, like trying to drive up a hill in the wrong gear. It's not tossing up any error codes.....
I immediately thought 'vacuum leak' (from running old carbed cars). but at idle it's pulling plenty of vacuum. Again, if it was my old Plymouth, I'd be thinking that the timing might be jumping around, as that's pretty much whatit feels like.
Long story short, is there something that these cars/engines are known for that might cause this issue?
A simple MAP or O2 sensor or something?
Cheers!

Damned67 wrote: I immediately thought 'vacuum leak' (from running old carbed cars). but at idle it's pulling plenty of vacuum.

G'day Damned,

I hope your problem doesn't have anything to do with your username Did you physically check your vacuum lines or rely on a guage? If you didn't physically check the hoses I suggest you get under there an check it all out, you'll be surprised what one hose can do under there yet not show up on a vacuum guage!

As for your other questions, I'll leave that to someone who has/had the same outback as you do

Cheers

Bennie

EGR Valve causing it to go slightly lean on cruise? Had it on a
Mazda 3 once... Just a thought.

EGR valve could be the culprit.

Bennie, when doing the upper engine cleaner, I did find a broken vac hose (which I replaced).... With the vac gauge, it did seem to be pulling a decent amount of vacuum. Then again, I'm used to old V8s with decent cams, so I guess it could still be low.
Anyone know what sort of vacuum the 2.5 should be pulling at idle?

Between 18 and 22inHg is where it should be.

Have you tried watching the vacuum gauge while you are driving to see if it changes when it surges?

Vac was certainly between 18-22, if not higher.... (22-25?)
Watching the vac gauge while driving would be ideal, but it's just a hand held gauge.

Next question. I assume there's O2 sensor downstream of the cat? If my cat was crapped out, what's the likelihood that could be the culprit of the surging?

In the last week, the car has developed a high pitched buzz/rattle when under certain load conditions, which I'm pretty sure is either the muffler or the cat falling apart.

Cheers!

Subaru's didnt get a 2nd o2 sensor till after 2003 on NA models (when OBD2 came in)

OK then, so my crapped out cat isn't going to be affecting my lugging/surging...
back to the drawing board...