2002 Forester that surges/hesitates/jolts with a rough/low/oscillating idle

[peterh]

Hi All,

 

I'm a new member and have never posted. I have a question regarding my 2002 Subaru Forester. Please forgive me for what might be an obvious question but I'm new at this.

 

My Forester has roughly 60,000 miles on it. Recently it has been surging/hesitating/jolting. It feels as though the car is on and off running out of gas. It happens to most when accelerating (especially up a hill) but is happens more lightly while cruising. Also, it seems to be inconsistent. Some days its worse and other days its not there at all (including the three times I took it to the mechanic). Also, the idle is rough/low. It seem to oscillate high and low every 2-3 seconds.

 

I changed the air filter, oil filter, fuel filter, and the spark plugs (spark plugs were in good condition). The fuel filter seemed to have fixed things but only temporarily. Two mechanics checked my car with a computer and a test drive and told me nothing was wrong with. One suggested I should clean the air intake and the other suggested I use an engine/injector cleaner. What seemed to work is the injector cleaner with a high octane fuel.

 

After driving for one take of high octane fuel, I switched back to the low octane fuel. Immediately, the problem returned. This has led me to believe that the problem is not that the injectors are dirty but that the car now needs high octane fuel for some reason. This is unusual given that have been driving it on low octane fuel since I bought it. Also, this would suggest (based on what I've been reading) that the problem could be engine knock. The only problem is that the term "engine knock" doesn't sound like an appropriate description of the problem. I don't hear any "knocking" or "pinging" sound. I could run it on high octane fuel but this seems like a bandaid rather than a solution to the problem.

 

Any suggestions are greatly appreciated.

 

Peter.

[cookie]

might be getting some water in the fuel. Hard to tell without being there. Try some dry gas in the tank.

[1 Lucky Texan]

I like the dry gas suggestion. And maybe try some Techron as well.(probably not in the same tankfull)

 

 

I'm always amazed at mechanics seemingly not wanting to believe the onwner of a car when they say thy've noticed a difference in their car's performance. Usually, even if they do detect something slight, they'll say it seems normal if they don't have a CEL or otherwise know how to proceed.

 

If your car 'seems' to require higher octane gas now than it has run well with in the past, you could try;

 

an ECU reset (disconnect neg. batt. term., step on brake pedal, wait 30 minutes, reconnect batt., re-evaluate after driving for a coupla weeks)

 

A Seafoam type treatment. perhaps the cylinders have carbon deposits which effectively raises the compression. (inspect plugs for carbon deposits - also, perhaps the system is running rich? possible Engine temp sensor malfunction?)

 

Read the ECU settings and see if the timing is adjusted reasonably.

 

Also, IAC and MAF (MAP) malfunctions might cause symptoms like this.

 

I hope someone else chimes in here. Subtle problems with no CEL codes are tricky.

[Commuter]

Texan covered most of the areas.

 

The only other thing I can think of is O2 sensor. Was it around this time that Subaru has issues with the O2 sensor?

 

The Phase I 2.5L (96-99) has some carbon issues, but I didn't think the Phase II engine did. And I would expect the problem to be much more consistent if it was carbon. I know that the MotorVac treatment fixed things for me. High octane fuel and over the counter additives won't do it if the carbon is really built up. Seafoam might though (from everything I keep hearing about it).

 

Since the car is responding differently to the octane level of the fuel, you may have some issue with the knock sensor. Subarus have been noted for overly sensitive knock sensors.

 

Let us know when you get it resolved.

 

Commuter

[cookie]

with a defective knock sensor? The only time I have had a similar problem was when the local gas station had water in one of thier tanks. The knock sensor scenario makes sense too.

[ferret]

Couldn't find the other thread I replied to....must have been too long ago.

 

I had this on MY02 Forester, My neighbor on his 01 Outback. Both were fornt O2 sensors. Ran great from startup....then 1/2 to an hr later, it acted like bad gas, or shutting the ignition off. Both cars were under warrenty. His was flatbedded to the dealer and ran great, until the next day.

No codes, nothing pointed to the O2 sensor, until I unplugged it and ran the engine in 'open loop' mode. Granted that set a code, but both ran great. We both had the same dealer, and both front O2 sensors were replaced. Trouble gone.

[cookie]

that seems like a good way to test too. If it was bad gas or a knock sensor the problem would not go away. I wonder if you were to disconnect the knock sensor if this would serve as a test for that? You would have to have something handy to clear the code.

[peterh]

Wow ... what a great response. Thanks! Based on your suggestions, I'll step through the following and let you know what worked:

 

1) Dry Gas: I've already tried different gas stations and they all have the same problem. I would guess that water in the gas is probably not the problem (unless my understanding of the phrase "water in the gas" is wrong). I don't think I've tried Techron though so I'll give that a try.

 

2) I'll try the ECU reset. This seems like an easy thing to try.

 

3) I'll try using Seafoam.

 

4) O2 sensor: I'll try this before the knock sensor. Is it ok for me to just unplug the O2 sensor and run the car as is? If it works better then I can assume I have to replace the O2 sensor? What is "open-loop" mode?

 

5) Knock sensor: As Cookie suggested, can I just unplug the knock sensor? Also, what does that mean to "clear a code"?

 

6) Texan suggested looking at the IAC and the MAF. At this point, I have no idea what these are but I'll look into them if steps 1-5 don't work.

 

Thanks in advance (again),

Peter.

[ferret]

4) Unplugging the O2 sensor WILL set a code. Reset it by disconnecting the battery for 15 mins or longer. Open loop mode is when there is no feedback to control mixture for emissions. Usually a vehicle default is to run rich.

 

I did it when the car was really acting up, pulled over, shut it off, then unplugged the sensor. The Ck Eng light will immediately come on, but you can drive away and the bucking is gone.

 

6, IAC is Idle air Control. Once you have the throttle open, this is out of the picture. Your 02 Forester has a MAP (Manifold Absolute Pressure) sensor. It can cause a no start, no run, but doesn't usually cause the intermittent problems seen with a contaminated MAF sensor strip. The TPS (Throttle position Sensor) can cause this, but when I have seen them do it, Subaru's usually set a code. (Mopar 4 bangers of the 80's and 90's rarely did however. And GM and Ford's are just as difficult to troubleshoot)

[cookie]

to get in there from one station or pump and stay until you run the gas out or put a can of dry gas in. If you have swirched stations and get exactly the same result odds are it is not water.

If you have water stay in the gas it stays on top of the fuel. Every time you run down to the same level the car sputters. You can also have it sputter on hills when the water hits the pickup. In the winter it is most miserable when the water can freeze in the gas line.

Throwing a code is when the check engine light comes on. The car computer stores the code that indicates a fault.If you unplug the ox sensor it will store a code that says faulty ox sensor. Maybe PO420. This helps a mechanic locate the problem.

To clear a code is to disconnect the battery or use a code reader on clear code setting. Not all codes will clear on a battery disconnect so I am glad to hear the Subaru ox sensor will clear this way.

I would follow the advice to test by disconnecting the ox sensor first I think.

I and a number of others on the board have my own code reader. At under $100 it is a good investment.

[color-blind]

Hi All,

 

I'm a new member and have never posted. I have a question regarding my 2002 Subaru Forester. Please forgive me for what might be an obvious question but I'm new at this.

 

My Forester has roughly 60,000 miles on it. Recently it has been surging/hesitating/jolting. It feels as though the car is on and off running out of gas. It happens to most when accelerating (especially up a hill) but is happens more lightly while cruising. Also, it seems to be inconsistent. Some days its worse and other days its not there at all (including the three times I took it to the mechanic). Also, the idle is rough/low. It seem to oscillate high and low every 2-3 seconds.

 

I changed the air filter, oil filter, fuel filter, and the spark plugs (spark plugs were in good condition). The fuel filter seemed to have fixed things but only temporarily. Two mechanics checked my car with a computer and a test drive and told me nothing was wrong with. One suggested I should clean the air intake and the other suggested I use an engine/injector cleaner. What seemed to work is the injector cleaner with a high octane fuel.

 

After driving for one take of high octane fuel, I switched back to the low octane fuel. Immediately, the problem returned. This has led me to believe that the problem is not that the injectors are dirty but that the car now needs high octane fuel for some reason. This is unusual given that have been driving it on low octane fuel since I bought it. Also, this would suggest (based on what I've been reading) that the problem could be engine knock. The only problem is that the term "engine knock" doesn't sound like an appropriate description of the problem. I don't hear any "knocking" or "pinging" sound. I could run it on high octane fuel but this seems like a bandaid rather than a solution to the problem.

 

Any suggestions are greatly appreciated.

 

Peter.

 

Sounds like your air fuel ratio sensor has failed. Basically it is the front oxygen sensor. Good luck

[peterh]

Hi All,

 

I tried resetting the ECU and it seemed to work for a day but the problems quickly returned.

 

In the mean time, the engine light turned on. I tried checking the code and it returned,

 

P0172 System too Rich (Bank 1)

 

I'm not sure how to fix this? An error for the oxygen sensor wasn't sense; however, could this still be the oxygen sensor?

 

Thanks in advance,

Peter.

[Storydude1]

to get in there from one station or pump and stay until you run the gas out or put a can of dry gas in. If you have swirched stations and get exactly the same result odds are it is not water.

If you have water stay in the gas it stays on top of the fuel. Every time you run down to the same level the car sputters. You can also have it sputter on hills when the water hits the pickup. In the winter it is most miserable when the water can freeze in the gas line.

Throwing a code is when the check engine light comes on. The car computer stores the code that indicates a fault.If you unplug the ox sensor it will store a code that says faulty ox sensor. Maybe PO420. This helps a mechanic locate the problem.

To clear a code is to disconnect the battery or use a code reader on clear code setting. Not all codes will clear on a battery disconnect so I am glad to hear the Subaru ox sensor will clear this way.

I would follow the advice to test by disconnecting the ox sensor first I think.

I and a number of others on the board have my own code reader. At under $100 it is a good investment.

 

 

Just to clairify..Gas floats on water. Otherwise oil spills would not be a big deal..it would all sink.

 

Water in a gas tank will sink to the bottom, and be picked up by the sending unit.

[sea#3]

Hi All,

 

I tried resetting the ECU and it seemed to work for a day but the problems quickly returned.

 

In the mean time, the engine light turned on. I tried checking the code and it returned,

 

P0172 System too Rich (Bank 1)

 

I'm not sure how to fix this? An error for the oxygen sensor wasn't sense; however, could this still be the oxygen sensor?

 

Thanks in advance,

Peter.

 

Replace the Front A/F sensor( 02 sensor ) and it will fix your problem

 

SEA#3

[1 Lucky Texan]

Replace the Front A/F sensor( 02 sensor ) and it will fix your problem

 

SEA#3

 

This seems quite possible. The fact that the car ran OK for a little while after the ECU reset probably means a sensor id bad, and the ECU is trying to alter it's map with bad input. If it isn't the O2 sensor, it's still quite likely another one.

[cookie]

I'm getting more senile. This is also why water drains for fuel tanks are on the bottom. Sometimes I type faster than my brain works.

[Storydude1]

I'm getting more senile. This is also why water drains for fuel tanks are on the bottom. Sometimes I type faster than my brain works.

Happens to the best of us..

[muse]

Peter-let us know what finally happens. I will be curious to hear the end result.

[trxeslr66]

I had a similar problem. I'm not clear if your having the hesitation when already in motion or not. Mine did it when taking off from a red light for example. Also sputtered when driving at a low speed in a parking lot or similar situation. I had the throttle body cleaned. It seems to have helped alot but after having it cleaned the check engine light came on. And it came on at a very convenient time, at the beginning of a 250 mile trip. Light went out after 250 miles and stayed out for the drive home. Came back on and off since then. Going to get codes from the mechanic next week. What a pain in my rump roast. Our mileage is the same also which makes me think it could be the throttle body. Its easy to do yourself.

[Lesbaru]

My gf has an 02 Forester (manual) that had a very similar problem. John at Williams Subaru in Lansing MI diagnosed it as a bad oxy sensor. Apparently the oxy sensors on those critters were exposed a bit more to the elements than usual and "burnt out" occaisionally. He replaced the bad sensor and no problems since.

[peterh]

Hi All,

 

I appreciate all the help I got from everyone! It turned out to be the front oxygen sensor. The good news is that I found out it's still under warrenty. I originally bought it in California and apparently California Foresters have an extra long warrenty for the emissions system.

 

Peter.

[cookie]

nice to hear it was simple and covered!