1998 Impreza OBS 77K 4EAT

At a stop light or stop sign, if I take off a little more than light throttle (say 20-30%) The car will stumble. Once it partially backfired when I let off the gas to prevent it from stumbling. It will come out of the stumble as soon as I let off or 3000 RPM's. I have drove impreza's since 1996. I have no CEL coming on, and I havn't pulled codes, but I think it may have to do with fuel.

Max

 

Today, it did it while in idle. I noticed that I can get around the problem by barely touching the gas just enough to start moving, then proceed as usual. This one has me stumped.

 

Just a thought but has the fuel fillter been changed.

 

I will change the fuel filter on saturday. Last night it threw a CEL. It come on while driving, then it flashed, now it just stays on? I wonder what the minutes worth of flashing meant? Thanks for the comments.



Max

 

Yesterday, before I was going to get a fuel filter, I went ahead and cleaned the TB with TB cleaner, then I cleaned the Mass Air Sensor, and the problem went away. Until today anyway, but it is not as intense. Oh well I am going to wait one more week for fuel filter and try to get the CEL to come on. Thanks for the comments.

Max

 

Just a thought but try running a good all around fuel system cleaner through the tank and see if you get an improvement. Also check the plugs, at 77k miles you surely need something...

 

Finally CEL light came on flashing. I believe the flash means misfire, now it stays on steady. Got the code pulled and it flashed p0302- Cyl #2 misfire. I suppose I will start with spark plugs, wires. Thanks for the replys.



Max

 

oh yeah i nearly forgot. You have a couple Oxygen sensors on the exaust pipes. I kinda doubt they are to the point where it would cause that but it can't hurt to change them.

 

Today, I replaced the spark plugs. CYL 2 & 4 had a problem. The washer on the NGK's were not flat against the cyl head. One side was against the seat of the spark plug, and the opposite side of the washer wasup a few placeson the thread. Both 2 & 4 show carbon past the washer. Obviously this would likely be the problem.

So I put new NGK's in, and I took the car for a spin. Wheew! No more hesiation. Then at the end of the day, it hesitates, and stumbles bad. especially with A/C on.

So if we review, a couple weeks ago, I clean the TB and MAS...

Problem goes away, good driving car. Until the end of the day.

Today, I replace spark plugs...

Problem goes away, good driving car. Until end of the day.

Then the same stumble comes back. I will still say with a long time of driving soobs, this is not the normal hesitation. Something is wierd if the car seems great after fixing other parts then goes back to driving bad.


Any info is much obliged!

Max

 

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max, did you get the coil tested, and when was the last time you had the wires replaced? Usualy fouled out plugs wouldent be that inconsistent but a bad wire, loose connection, or a coil pack going bad might. Almost every time i have had a probablem like that it was a cyilinder not fireing (especially when its cold). and most of the time it was wires.

 

Finally replaced fuel filter, it still happens but it is musch better. Bust still staying on course, it is still worse than the normal Subaru hesitation. I am going to get spark plug wires next, but wanted to ask a question about oxygen sensors...

If I needed to replace 1 oxygen sensor first which pertains to my problem which one would I need to replace?

IIRC the front O2 sensor tells whether the engine is rich/lean and is the one that adjusts the fuel (i think this is the one that need attention!) and the 2nd O2 sensor reflects the status of the cats, if they become crappy the CEL pops up right?

Pretty sure that how it goes.

Thanks for your responses!

MAX

 

yes you are correct...... it may be a bad cat..... cuz the front O2 sensor is like a before reading.... and the second O2 is the after reading.... between the two reading the ECU should read different. it doesnt it will set a fault which may end up being a bad cat(misfires are VERY harmful to the cat)-just keep that in mind. hope this helps you man.

 

I don't really see the o2 sensors being the culprits. The easy way to be certain is see if it ever does it when you floor the gas- if it still bogs, then it isnt the sensors since they weren't referenced.

Unplug the maf and drive it. If the problem goes away, there you go. This will make you run pretty rich, and give you some poor mpg while unplugged.

Because they're easy to do, i would give it an italian tune up and the Windows treatment. Run the **** out of it for a couple short trips (like go 35 in 2nd and floor it when possible) and unplug the battery and plug it back in after an hour, clearing the memory.

The last one i'd try is unplugging the knock sensor.

Beyond that, it gets harder to identify.