1998 Legacy Outback Wagon 2.5 Auto

My car started to develop a severe miss or stumble whenever I pull out from a stop. It is so bad it feels like it is going to stall. Then it clears up and runs fine. I also notice it when I am cruising along, barely giving it any throttle, and then try to accelerate. Or if the car tries to downshift when I am barely giving it any throttle. At high speed it runs fine and I dont notice it at all. Its only in a very narrow area right above idle.

The check engine light came on, and the only code it was showing was a musfire on cylinder 3, so I had the coil pack replaced. The check engine light went out, but the miss is still there. I also tried several bottles of fuel system cleaners when this all started, without any effect.

What would cause this behavior? My mechanic wants to replace plugs and wires as the next step, but I'm thinking it is some type of fuel or sensor problem.

you get a code for a misfire on cyl 3, but think it is a sensor or fuel related issue? really?

misfires can, and do, foul and/or damage the spark plug.. change them. it is relatively cheap...

same with wires... not that expensive - but do NOT use the cheap parts store brand wires... OEM or NGK ONLY.

Then, and only then, do you look for other causes if the issue still persists.

It's most likely spark (plugs/wires) or sensor related.  there's a lot of possibilities....if it's closely related to throttle input or a narrow band I would suspect the idle controller or throttle position sensor or dirty throttle body.  

1. spark plugs and wires - what brand and how old are they?  if not NGK, unknown age/mileage, or they're old - then that's an even more likely starting point.

2. knock sensor - ebay specials are $8 and it's one 12mm bolt to replace it.  so easy and cheap and by far the most common failure on that engine i would routinely replacing them when working on someone elses car. 

3. MAF or TPS

I also think TPS needs to be checked. along with catching-up on any maintenance.

look for oil on plug wire boots, could need VC gaskets.

 

TPS is what signals the ECU that you are wanting more fuel, if that signal is wrong, the car can lean-out too much.

If you can duplicate this at idle, spray some starter fluid into the intake when the engine stumbles just above idle -  if it runs smoother, probably some fueling issue.

Edited December 5, 20187 yr by 1 Lucky Texan

Thanks for the suggestions. I travel 65 miles to work, sometimes up to 80mph on the expressways, and it runs and accelerates fine at those speeds. It's just at that one particular point that it misses, so I didnt think plugs or wires would act that way.

ah - that is interesting - if it's at a precise point that sure sounds like it could be TPS 

they can be tested 

i might have a TPS for that car - post a picture.  i know i have a 98 automatic TPS, but I removed it for someone else who never got it so not sure where i put it. 

Update: I noticed that it does not stumble if the car is cold, or if I pull out very slowly. I just grabbed some plugs and wires and headed out to my mechanic, and on the way there, the check engine light began to blink again, then stayed on solid. Code came back misfire on cyl 3 again. He is looking at it now.

He said he is going to clean the throttle bidy and look at the injectors.

How do you check the TPS?

injector - that's a wise suggestion.  i'm not sure why i suggested TPS, Knock, MAF when you have a cylinder misfire. 

cylinder misfire the plugs and wires need tested/swapped, or replaced.  injector is a good next step since those are cylinder dependent. 

flashing CEL means "multiple cylinder misfire".  might have had a momentary time of multiple misfires. 

the mechanic could swap injectors from cylinder 1 and 3 and see if the misfire "moves" to cylinder 1, then you'll know it's the injector causing it. 

 

an analog ohmmeter might show jerkiness/drop-outs as the tps is moved thru its range. Your mechanic may be able to monitor for voltage jumps while idling the car....not sure on that.

Final update:

Mechanic tested injector and didnt find any issues. Cleaned throttlebody. Replaced plugs and wires. Noticed that plug wire #3 had several burn marks on side facing motor.

Car is running perfectly now, so must have been wire #3 arcing that caused the issue.

Thanks again for everyones input.

The second poster "Heartless" had this problem nailed immediately!  And then none of the subsequent posters even asked the OP to specify how old the SP or wires were,and he never specified.   Almost everyone besides Heartless missed the easy, first step.

Heartless is intelligent and logical.  (Love ya, Babe!!!)

thanks guys, but that was experience talking there.. been there, done that a couple of times now, LOL

first time it happened was on the old GL, bad parts store wires, one started arcing through the boot at the plug end.. was a good couple hours away from home when it started.. a few good wraps of electrical tape got me home. Ordered some NGK wires right away.

2nd time it was on the 95 Legacy - the coil pack had gone bad.. would only do it (stumble/misfire) when it was damp out, too...I could see the arcing, even in broad daylight, when i popped the hood.

 

Edited December 8, 20187 yr by heartless