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2001 Forester 5 speed
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Discussion Starter #1
I am getting a weird issue with my 01 Forester seems like its either an O2 sensor or the throttle position sensor(assuming this car has something like that). Sometimes when driving and just about any time I go up a hill the car has a fit. The best way I can describe it is the engine seems to have an epileptic seizure it will stutter and chug and then race and then its OK for a min or two and then it starts again. It idles at around 500-700 with a lobbing miss which makes me think its going to stall at any second.

Took it to a Subaru dealer and had the timing belt changed, found out I needed a knock sensor (CEL). Replaced plugs, air & fuel filters, new knock sensor(made the CEL go out but didn't help the performance).

I have searched through the forums here and things seem to indicate that I have an issues with the O2 sensor which I'm going to try tonight provided I can get the car home. But could something like a throttle sensor cause the same issues and is there a way to test these two sensors before I start tossing money at them.
 

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04 Forester X, MT
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Have you cleaned your throttle body and Idle Air Control Valve? Not sure if this could cause uphill surging or not but it would definitely effect idle speed.
(I believe all '01s had?!) Some other details would help: miles, turbo or N/A (trim), 4EAT or 5MT.

O2 sensors generally go about 100,000 miles before problems. My past 2 '00s had theirs replaced under warranty before I got them and I didn't quite get to the point to replace on the second. I did have to replace on my '04 at about 90,000 b/c the heater circuit went out and threw code.

The do have TPS. I'm not sure how to test as mine have not yet gone bad. I would say it is a definite possibility but then the cars are pretty good at throwing codes (such as the knock sensor you mentioned, crank and cam sensors, misfires for various reasons, etc.).

Have you run it a lot with less than 1/4 tank of fuel? The fuel pump could be on the fritz as well. I got the surge/buck a couple of times after almost running out of fuel but didn't have to replace the fuel pump. Considering the cost and others' experiences, I'll probably do mine about 150,000 mi as preventive maintenance on my '04.
 

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2001 Forester 5 speed
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Discussion Starter #3
The throttle body has been cleaned (at least the best I could do without taking off, should I remove it completely to clean it?) but not the IACV. It's a 2001 2.5L N/A, 5 speed about 140,000 miles. Normally I run the car to about 1/4 tank and the fill it but I never let it get below 1/8 even at the worst of times (I have never seen a low fuel light) today I was driving it and had about a 1/2 a tank of gas and the things was acting horrible. I got a cheap code reader and a Haynes manual for this thing tonight at Autozone and I will check to see if any codes are still stuck in the ECU and I guess I will yank the O2 sensor and test it tomorrow to see what it does.
 

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2001 Forester 5 speed
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Discussion Starter #4
Just checked the codes and its giving me a p301 ,302, 303. Don't know if this is accurate though as I forgot to connected one of my plug wires when I was changing the plugs and started it up and it gave me an error then so it might be the same code. I am going to clear the codes and check my coil pack and the plug wires for a break.
 

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04 Forester X, MT
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Throttle body is OK to clean on car because it still has cable and is easy to open throttle to clean backside and inside with car off (versus drive-by-wire throttle control with electronic module - haven't done one of those on a subaru yet). I cleaned mine last weekend. You clean inside some with the car off and crank it and spray some in with it running too. Be sure it is safe for electronics and not just "carburetor cleaner". I did try to avoid spraying some on the shaft joint at the TPS. It's easy to remove the IACV and clean it and the seat area off too. It's on top of the throttle body with blue sticker, electrical connector and 2 small screws mounting it. Be careful not to drop the screws or damage the o-ring seal if you decide to clean it too.

Sounds like coil and/or wires is a good next step. Be sure and use a light coating of dielectric grease on the boots and connections. Moisture as well as heat often times make some noticeable difference with coil problem symptoms.

Don't forget fuel pumps can cause symptoms with no codes.

If you're still on the original O2 sensor I would plan on changing it when you can afford it rather than waiting for it to go completely bad.

To be clear the performance issue was there both before and after the dealer changed the timing belt and other parts and symptoms didn't change noticeably?
 

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2001 Forester 5 speed
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Discussion Starter #6
The symptons were there to a point before the timing belt change but seemed to have gotten worse over the past month or so (been about 2 months since the TB was changed) it didnt like hills before the change but the stuttering is a fairly new development.
 

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2001 Forester 5 speed
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Discussion Starter #7
Just checked the resistance on the coil pack the secondary looks ok but the primary isn't showing up at all does that mean its dead?
 

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1998 Forester
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39 Posts
Just checked the resistance on the coil pack the secondary looks ok but the primary isn't showing up at all does that mean its dead?
When you test the primary, does the meter show infinite resistance i.e. it's open or no resistance at all i.e you have continuity? I would expect the primary to be almost a dead short.

Since the car runs, albeit somewhat badly, I would suspect a fuel system problem, since a misfire or spark problem would likely throw a code.........
 

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2001 Forester 5 speed
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Discussion Starter #9 (Edited)
When I test it I get 0L ohms on all the meters I have tried 2 cheapy pocket multi-meters and 1 pretty good one that I use for everything at work, all of them at giving me 0L. But when I go to the secondaries I get about 13kohms which is in spec according to the Hayens manual. I tried doing a continuity test and I get nothing. But if I test between pins 2&3 I get a resistance of 1.3Mohms don't know if that is supposed to happen or not.

As far as the codes it actually did throw the coded for misfire on 1,2,3 but im not getting a CEL just the codes from the reader so they might be old.

I guess I can get a fuel pressure gauge to test the fuel pump but I didn't want to buy more tools if I didn't have to.
 

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1998 Forester
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When I test it I get 0L ohms on all the meters I have tried 2 cheapy pocket multi-meters and 1 pretty good one that I use for everything at work, all of them at giving me 0L. But when I go to the secondaries I get about 13kohms which is in spec according to the Hayens manual. I tried doing a continuity test and I get nothing. But if I test between pins 2&3 I get a resistance of 1.3Mohms don't know if that is supposed to happen or not.

As far as the codes it actually did throw the coded for misfire on 1,2,3 but im not getting a CEL just the codes from the reader so they might be old.

I guess I can get a fuel pressure gauge to test the fuel pump but I didn't want to buy more tools if I didn't have to.
I don't know what 0L means. Is that what you see when the probes are not connected to anything? What is displayed when the probes are touched to each other? There may be a diode that blocks the current in one direction or it may be a transistor junction. Try reversing the probe leads.

Regarding the CEL, perhaps it's burnt out or disconnected. Erase the codes from the ECU, take a drive, then do a code reading. That will give you a real view of whats happening.

For a pressure tester, it's possible to assemble one from fittings, fuel line hose, hose clamps and a 0-100 psi water gauge for about $30. How much does your local mechanic charge an hour?
 

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2001 Forester 5 speed
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Discussion Starter #11
I don't know what 0L means. Is that what you see when the probes are not connected to anything? What is displayed when the probes are touched to each other? There may be a diode that blocks the current in one direction or it may be a transistor junction. Try reversing the probe leads.The 0L is what my multimeters display when they read nothing (open circuit) when I touch the leads together I get a reading. As to the diode I checked it in every way possible so I don't think it has a one way diode. The only other thing I can think of is that maybe my meters don't have enough juice to push through the coils and that's why reporting that its an open circuit.

Regarding the CEL, perhaps it's burnt out or disconnected. Erase the codes from the ECU, take a drive, then do a code reading. That will give you a real view of whats happening.Thats a good point I did notice that my code readed said it the CEL was on but its goofy with that sometimes. I will clear the code and run it here after while when i get a chance, stuck at work right now.

How much does your local mechanic charge an hour?MY local Subaru shop was less than helpful I took it to them they charged me about 100$ for diagnostics and told me nothing and then insulted me and told me to "quit fiddling with the with the car", so I am avoiding them like the plague.
I'm going to change the plug wires and check the plugs again for good measure and run it after clearing the codes to see if I get the error at least I will eliminate the cheap parts as the problem.
 

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2001 Forester 5 speed
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Discussion Starter #12
Ok just changed the plug wires restarted the car with the OBDII scanner connected and I get all 4 cylinders misfiring and a P0172 error which tells me bank #1 is too rich. Is this because of the O2 or could it be the MAP/MAF which ever this thing has. The idle did level out some and the resistance on the new wires is about 8.5 ohms vs the 18ohms I was getting from the old ones.
 

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2001 Forester 5 speed
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Discussion Starter #14
well I think Im going to try and test the O2 sensor on the car just to be safe. hate to buy a new coil pack at 200$ if its actually ok and the O2 is the thing thats bad. O2 is way cheaper
 

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04 Forester X, MT
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wow, $200 is pretty pricey. sounds like a good plan.
 

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1998 Forester
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well I think Im going to try and test the O2 sensor on the car just to be safe. hate to buy a new coil pack at 200$ if its actually ok and the O2 is the thing thats bad. O2 is way cheaper
The O2 sensors don't actually do much of anything until they have warmed up ~5 minutes then the ECU goes from an 'open loop state' to a 'closed loop state' and starts to regulate the fuel flow closely.

I have a random problem similar to yours but I think yours is related to fuel pressure and the electrical issues with misfires. The Haynes manual details how to do a stimulus/ response test for the fuel flow in detail without a pressure gauge.

If you pull apart the O2 connectors you should see the O2 sensors code fault on the ECU.
 

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2001 Forester 5 speed
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Discussion Starter #17
dharmashiv ... sweet thanks for the info I just got my Haynes for it and haven't been completely through it yet. I will try the stimulus/response test next chance I get. I did notice that after clearing the codes and running the car for about 30 miles or so it seems to have gotten a little better, but its still not perfect. Seems to be driveable unless I kick the AC on then it wants to bog down to almost a stall if I'm sitting at idle. I was going to try to just disconnect the O2 and see if it would give me a code but I didn't know if it would run without the O2 plugged in. May have to wait a days or two to test it out between work and the storms we have been getting I haven't had much time to turn wrenches.

On a side note it seems that Autozone and Adavance Auto (the two major parts stores in my area) have a vaccum/pressure gauge that will do fuel for about 20 bucks. But if haynes way of doing things is easy enough I may just go ahead and save the 20 bucks.
 

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2001 Forester 5 speed
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Discussion Starter #18
Just an update. I think I may have figured out the problem (or at least a part of the problem). Oil. The seals around my spark plugs are leaking a bit. I didn't think much of it because I have had a number of cars in the past (not subies) that have had leaky valve pans and never caused any real issues aside from a dirty engine and the smell of burnt oil. I was reading another posting somewhere (maybe here) that talked about the oil getting into the silicone boot of the plug wire and making it conductive. So I have new wires installed (about a week old) and the performance is slowly going back down to how it was before I changed them, so I'm thinking this may have something to do with it. So if work allows for it I hope to be changing the valve cover seals this weekend and apparently getting yet another set of plug wires (gad I got the cheap ones).
 

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2014 Impreza Ltd CVT
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Let me chime in here ..... I was chasing a neighbors 2003 Outback for a problem that sounds similar to this.

Cold start ... all fine

Few minutes after warmup ...... BAD BAD IDLE ... stalling about 300 rpm

After warmup .... All was fine once more until the next cooldown.

After MANY dollars at a dealer ( front O2 sensor, TPS, Engine Temp Sensor, Plugs, Wires, Throttle body Cleaning ), I asked him to let it with me 1 overnight. In the morning, I put my PC attached OBDII reader on it and monitored: MAP, TPS, Ambient Temp and Short Fuel Trim.

As on schedule it started to act up about 5 minutes after startup. Only thing I noticed on the display was the MAP went from 9.8 to 14 and bounced around there.

So it's either a defective MAP ....... OR the idle solenoid closing down, forcing the manifold pressure to go up. Now they CLEANED the throttle body, so I shut it down and removed the IACV ( idle solenoid ). It looked fine, felt the inside opening and there were no sharp edges or burrs. Pintle looked clean, but a little too dry. So I put a thin coating of silicone oil ( could have used brake fluid as that's a good lubricant for seals ). My thought was it MAY be sticking during warmup. Put it back together and called him.

Told him if this doesn't fix it, either the MAP is defective ...... or the IACV. Neither is cheap. That was last Sunday.

This afternoon he was on the answering machine when I got home ....... told me I was a Subaru god of a mechanic ........ Said it never ran so well.

I think a lot of that may be in his mind ..... because what I did was fix a 5 - 10 minute warmup problem he had.

I searched .... the IACV is 22650AA192 and lists for $345 from Subaru. If I needed one, I might just go to Ebay and buy an entire used throttle body with one on it. I see the entire throttle bodies for under $100 with the TPS and IACV at a minimum on them.
 

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2001 Forester 5 speed
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Discussion Starter #20
Thanks for the info I will give that a try. I just changed the the valve cover seals along with the spark plug well seals. That seems to have taken some of the high speed missing issues out. Which I still found to be really odd. But I guess I have some more work to do after I get my CV axel changed (ripped boot)
 
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