Forester threw a maf sensor code a couple of weeks back, about the same time it started doing this chug chug chug under load. Needless to say I ASSUMED a new MAF would fix it. Got "new" MAF in yesterday and have been monitoring codes for a short while now while waiting on funds for new maf and for the maf to come in the mail.

 

Here's the rub, I threw the new maf on last night and same crap. It's hard to describe other than a cyclic misfire feeling that doesn't happen "every" revolution. its more like a heavy hesitation that comes and goes in rhythm. Looking at my live data before on my scanner, the maf readings were going bonkers... steady under low load. Guess it was just rpm related.

 

Ignition timing is steady through this ordeal too. My second thought was counting knock, but not that I can tell because timing isn't retarding according to live data...

 

The last 2 times I pulled codes last night/last week I got a DTC for long term fuel trim bank 1.

 

Last night when I pulled codes, I got cyl3 and cyl4 misfire but had no bucking to back it up.

 

No o2 codes and my scanner has graph and output looks good on both o2 sensors. I'm stumped.

 

new fuel filter a while back, new NGK plug wires, new NGK plugs.

 

No codes concerning CKP, or CMP sensors.

What's your MAP / Baro pressure value during all this? Throttle sensor values?

map won't show on my scanner but TPS is smooth as glass. did a voltage sweep on it and it is linear. :-\

 

I may need to call in the pros on this one... i sure don't want to take it to the dealer...

bump. at whits end

I'd start by looking for a vacuum leak somewhere.

 

I don't know which years have MAP sensors and which didn't. Yours may not have one. The ECU still uses a MAP value but it calculates it based on input from other sensors. This value should still be visible on a scanner, but it may depend on the scanner.

 

BTW what year is this thing? 2.2 or 2.5?

grabbed a map sensor at junkyard this morning while getting a knock sensor and evap solenoid for my car. threw it on and VIOLA! no more chug chug.:banana: