Engine Stubles & Misses ?

[00Legacy]

Here's one the dealer can't figure. Maybe some of the "Gurus" on here can help. I have the 00 Legacy 4 dr sedan with the 2.5 engine w/auto trans. Here's the problem. There are times that the car will run great, engine runs nice and smooth, trans shifts normal. Then, out of know where, the engine starts missing, shaking, looses power & has stalled once. Does not matter what the weather is. Can happen at any time.

I took the car to the Subaru dealer & explained what was going on. They kept the car for to days. They said there was no trouble codes showing. They finally said the injectors needed clean & gas filter changed.

So, after $175 I get the car back, & in 2 days started acting up again just like before. Took it the dealer, and then they said the throttle body needed cleaned & that would cost $105. They had already did that before my approval. So, at least I didn't have to pay for that.

I ask the service tech if maybe the throttle position sensor could be bad, and he said no, that it would show up on the on the code readout. I said you can't rely on computers completely. (He didn't like that remark)

This has been getting worst as time goes on. But, there are still times that the car runs like new.

I have installed new plus, wires & both o2 sensors.

Hope someone can give me and idea what to look for or test. I really don't want to go back to the dealer. Anyone can change parts & eventually fix the problem.

The car has 134,000 miles.

Didn't mean to make this post so long.

thanks

[Dynamic Entry]

I didn't realize the more modern Legacy does this too. Mine is extremely tempermental also, and I am not alone.

Some days it is a champ, and others it seems to be in limp mode.

The more parts I clean and replace the more consistently better the car runs. But my experience is that no one can point to one or two definite parts for the stumbling/missing symptoms.

Some people have had luck by cleaning/replacing/upgrading the electrical grounds

some people have solved their stumbling with a new alternator

new plugs and wires will always help (I realize you have done this already)

so electrical is a big thing, but also the vaccum lines are critical

you can check/replace all the breathers that connect the intake and block. the PCV system and the PCV valve itself are also commonly in need of some attention

we also have the fuel pump and fuel filter to pay attention to....


and you are right in being frustrated, dealers like to just replace things and hope it works. good way to make money. but many of the things I mentioned above you can check/clean yourself and see if it makes a difference

last weekend I drove to the coast and back (~2000 KM) and while there my car began to have trouble starting. the solenoid would just click furiously without the motor turning at all, then sometimes it would catch. And the electrical was acting really strange; the battery wasn't weak but acted weak when ON/START, and the tach and stereo seemed to short/freak out.

I cleaned the terminal connections and it went back to firing up on the first turn.


I also didn't mean to make this post so long, and especially since it isn't very helpful.

Good luck and maybe someone else can be more resolute about where you should start. Any N/A guys out there?

[00Legacy]

Some good advice taken and will try these things. One thing, when this starts acting up, the idle is erratic. Goes from around 500 to 1000 rpm. But when put in drive, it is stable until I get to any speed.

Also, when in neutral, I rev up the engine a bit, say to around 1600 and quickly release, it stays at 1600 or 1500 for a few seconds before idling back down.

Again, I've explained these things to the dealer, and they look at me with a "DUH" look.......

I will try these things you mentioned.

If the alternator is failing at times, wouldn't that make the accessories act weird?

I'm old school when it comes to cars. Give me back the days when all you had to do is look under the hood of a vehicle and say, there's the engine!! Now let me go to work on it with my hammer & pliers.........

I'm getting to the point of doing just that with this problem......1st time I've ever had any thing wrong, so I guess I can't complain to much.

[Legacy777]

MAF Sensor.

Been there, done that....and cussed a lot.

[00Legacy]

The MAF sensor could do that & not show a code? Man, if that would be it!! Btw, I've been saying more saying more than my share of cuss words.......

[00Legacy]

Is this MAF sensor something you clean, or replace? Is there a way to test if it is in fact bad?

[206er]

first thing to try would be to spray it out with maf cleaner. DO NOT touch the element in any physical way you will break it for sure. also what kind of air filter are you running?

on my dad's sohc legacy 2.5 automatic it began misfiring one very hot day. the ecu had detected a misfire or knock or something and apparenly cut spark to the cylinder(???). I pulled the codes and misfire on cyl 1. cleared teh codes and new plug and it went away. we thought head gasket at first because it was blowing white smoke and misfiring badly.

[00Legacy]

Is the MAF & MAP the same thing? The reason for asking is that my Haynes Manual doesn't say anything about a MAP Sensor until the 2004 year & up. It shows the MAP Sensor for my 2000 Legacy located on the intake manifold.

It goes on to say that the MAF is on the throttle body for the turbo charged engines.

So, is the MAF & MAP one in the same?

Hope this isn't getting to confusing......

[mike-tracy]

They are similar in that they measure air coming into the engine. MAP measures Manifold Absolute Pressure while MAF measures Air Flow.

[Legacy777]

If your Legacy is MAP based only then my theory on the MAF sensor is not correct.

The MAF sensor should be near the airbox and airfilter

[00Legacy]

I located the MAP attached to the intake. I removed it and was somewhat dirty. I then installed it back. There isn't anything sensor connected to the air box.

While I was at it, I removed the PVC (I think) and it was really dirty & wasn't rattling. After a good clean, I reinstalled that. I checked all the vac lines & electric connection with a touch of die-electric grease.

After doing this, the engine idles smoothly at startup, but after a few minutes, the same thing is happening......

I tried something different. While in gear & brakes on, I gave it gas up to around 2000 RPM. Then the engine started shaking & loosing power. I even floored it while braking. Not long, as I didn't want to hurt the tranny.

[tahiti350]

Sounds like you have the same problem I'm having... Fun isn't it.

[mike-tracy]

On my newer Legacy, I had similar problems. No codes either. And very intermittent.

I cleaned the grounds in the engine bay and unplugged the ECU (under the front passenger's seat), tried a different known good ECU, and it worked good. Put my ECU back in and it worked good also. So between the grounds and reseating my ECU, the problem went away and hasn't come back.

[tahiti350]

Just fixed mine!!! swapped MAF/upper aircleaner housing with my other Leg, went out for a 50 mile drive around town and no stumble!!

[00Legacy]

Ok, i'll clean all the grounds I see, and pull the plug off the ecu and re-plug. Would it be ok to put die-electric grease on all the electric connections?

Thanks so far for all the input on this......

[mike-tracy]

I did that (dielectric grease) on the grounds & plugs in the engine bay. It's cheap insurance to avoid connection problems in the future. I didn't put any on the ECU, because due to it's location mine looked as new as the day it came from the factory.