I have been troubleshooting this car for three days and want to burn it to the ground.

2002 outback 2.5 137k manual trans.

Headgaskets replaced @ 130k (dealer)

front A/f ratio sensor @132k (dealer)

Alt 120k (dealer)

 

Ok the car has a poor idle and wants to stall / buck from a stop. At freeway speeds it has surges at 2500.

 

Work performed today:

Valve adjustment

new ngk plugs

new coil (aftermarket)

new plug wires (aftermarket changed twice 2 brands)

cleaned throttle body

Inspected and adjusted tp sensor

no codes

performed cylinder ballance test (miss not following cylinders)

new fuel filter

fuel pressure 33 unplugged fuel pressure sensor pressure 39

squeezed off fuel pressure return line (pressure rose to 70) no change to miss

 

Dont know what to try next! Thanks for the help

any check engine lights now or ever?

 

i had a bad misfire once that went away when i swapped the entire intake manifold with another one. that's completely anecdotal but i had done basically everything you did and that was an easy attempt i could make, got lucky.

Codes once for misfire on #3 and #4 but has not returned. I just unhooked the battery for 30 min for a hard re learn we will see.

Well my forester started bucking, surging and poor idel like yours, it was the upstream o2 sensor. If you unplug it and it runs better, that what it is. worked good for me!

 

Good luck!

Well my forester started bucking, surging and poor idel like yours, it was the upstream o2 sensor. If you unplug it and it runs better, that what it is. worked good for me!

 

Good luck!

 

it's only the front sensors, as in his case, that can affect running. the rear is emissions only and can be ignored entirely.

 

good to know you can still disconnect front O2 sensors in newer stuff, i hadn't had to try that yet.

it's only the front sensors, as in his case, that can affect running. the rear is emissions only and can be ignored entirely.

 

good to know you can still disconnect front O2 sensors in newer stuff, i hadn't had to try that yet.

 

It worked great with our it, till the new one came and saved time not having a code reader. Lol

It could still be plug wires..believe it or not.

 

2.5's are moody.

 

"store brand" plug wires? You could try many sets of them with no/little success.

 

Hate it when the obvious things don't fix a problem.

 

The fact that is was 3&4 miss means to me(IMO) it's electrical.

No change after battery disconnect. Dealer wires are the next step... I will try driving it with A/F ratio sensor unplugged.

Maybe put a better location in your profile.

 

Perhaps a member is close and you can swap wires (and maybe other things) to see what's happenning. "Known good" and "verified bad" can both be very helpful.

 

I've done stuff like that for local members. I don't have any of the newer stuff like you need though.

Good idea.

I have had excellent results with NKG spark plug wires in my Forester, FWIW. Does anyone think it's worthwhile checking the vacuum? Checking the vacuum is a cheap and easy test that can rule in/rule out quite a few things. An air leak anywhere behind the MAF sensor can cause a number of strange idle related problems.

No change unplugging the A/F sensor Still bucks still idles poor.

When you cleaned the throttle body, did you take apart the idle air control valve and clean the pintle and the inside of the port it goes into?

my old 110k mile forester had a plugged cat and had an almost cyclic stumble in the low range. I unscrewed the front o2 sensor and drove it around and viola! ran like a champ. $130 ebay bolt on catalytic converter later and she was ready to roll.

 

I looked into the old cat with a flashlight and the ceramic core had melted down and blocked the exhaust flow.

Vacuum check is a good idea. I changed mine- hoses on the Forester and couldn't believe the difference in performance and there was not one visible imperfection in the originals.

Just a question, I have been here for years and never of "front A/f ratio sensor" what part is this.

Thanks

he means O2 sensor

PCV replaced????

Removed and cleaned the idle control valve. No change. New pcv valve and hose last year, checked valve yesterday looked good not plugged.

Cleaned the MAF yet?

Try unplugging it.

 

Symptoms sound like low speed leaness to me.

I would check the O2 sensor output w/a scanner or voltmeter.

Manifold vacuum too.

 

Also carefully inspect the hoses between the MAF and the throttle body for cracks,looseness or leaks.A leak here won`t show on the vacuum gauge but will mess up the low speed mixture.May well reveal itself thru low O2 sensor voltage.

I see this scenario a lot on various cars.Mazda Tribute last week.

How come nobody has mentioned the knock sensor? Even if there are no codes, a bad knock sensor can make your car run like crap. AFAIK, one of the symptoms is the engine has no stamina below 2500 RPM. It's worth checking.

 

PD: when you decide to junk it, let me know. I'll give you $50 more than the junkyard

How come nobody has mentioned the knock sensor? Even if there are no codes, a bad knock sensor can make your car run like crap. AFAIK, one of the symptoms is the engine has no stamina below 2500 RPM. It's worth checking.

 

PD: when you decide to junk it, let me know. I'll give you $50 more than the junkyard

 

I've never seen a knock sensor cause a miss. Which I believe was the original problem.

 

Sluggish performance without a possible CEL - yes. But never seen a knock sensor cause a miss.

 

Guess there is always a first time...

Cleaned the MAF yet?

02 outback is speed-density EFI, no MAF sensor, only MAP. That's why they're super sensitive to vacuum leaks.

The miss may be a red herring... specially if the OP was running aftermarket wires.

 

In any case, it's a cheap intervention that *may* fix the main issue (poor performance)

 

I've never seen a knock sensor cause a miss. Which I believe was the original problem.

 

Sluggish performance without a possible CEL - yes. But never seen a knock sensor cause a miss.

 

Guess there is always a first time...

Thanks everyone for using your brains on this one. I'm swapping the map out with buddys forester tomorrow. I scoped out the knock sensor by hitting the block with a hammer and saw the signal get larger the harder I hit it. The motor mount and trans mount seam a little loose in 4th gear full throttle stab there is movement in the shifter about a inch. I will rescope it while driving and see if it is picking up the bang in the mounts. I did drive it with the knock sensor unplugged and it may no change other than kicking a code for it.

Vacuum update: I checked it with a smoke machine and found no leaks. The vacuum gauge shows 21 hg cold (1-2 lbs flutter) warm 18 hg ( 2-3 lbs flutter) The exhaust smells lean. I wonder if the pcm needs a reflash?