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1998 Forester, 2.0 awd
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Discussion Starter #1
Hi, I've just purchased a '98 Forester non turbo and it hesitates on acceleration, hot or cold. Also fuel consumption seem high but there is no apparent smoking on acceleration.
Have changed the plugs, leads, fuel, oil and air filter. Just done the cambelt and changed everything there.
Knock sensor seems to be fine on the multimeter, timing advances ok when reving when checked with timing light.
Have cleaned out the throttle body and checked every connector I could lay my hands on.
The CEL is not coming up on the dash and my OBD2 reader won't connect but it did momentarily flash that there were no codes.
Any ideas where to go from next? - I will check the fuel pressure next, what should it be? and what volume for a 2.0l motor?
Cheers.
 

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1998 Forester
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213 Posts
Fuel pressure on a 2.5l should be 33-40 psi. Also I would try cleaning the mass air flow and flush the fuel injectors. If checking the fuel pressure it would be a good time to replace the fuel filter.
 

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2001 Forester S Premium
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106 Posts
Probably your problem is the IACV. You can try to clean it first, and reset ecu to see what happens.
 

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377 Posts
Occasionally, I've read of folks w/ similar problems; drivability issues and no CEL, and the fix was eventually to replace the O2 sensor. Apparently, sometimes the sensor provides faulty information, but not bad enough to trigger a code. A new O2 sensor is not expensive, and if yours has not been replaced recently, this may be worth a try. I've had good results w/ O2 sensors I purchased on ebay, either universal (lowest cost) or direct replacement.

good luck
 

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1998 Forester, 2.0 awd
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8 Posts
Discussion Starter #5
Thanks for ideas so far

Would the o2 sensor stiil affect the drivability when the motor is still cold and the other sensors haven't kicked in?
What is the IACV?, I don't know much about modern fuel injection trouble shooting as all my experience in in older cars with multiple carbs.
Cheers.
 

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O2 sensor problem would be sensitive to hot or cold engine, since open loop fuel control is used during cold engine. O2 sesnor controls closed loop fuel control w/ warm engine.

Significant air leak might cause the problem. Check for leaks w/ throttle body cleaner. Idle speed will change when cleaner is ingested.

good luck
 

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04 Forester X, MT
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1,039 Posts
- disclaimer - Most everyone here is talking 2.5L for North America. I have no idea how similar or different to 2.0 L you have there.

IACV is Idle Air Control Valve. It is mounted on top of the throttle body with a blue sticker. I'm not sure it would cause hesitation on acceleration, but I suppose it is possible. Mine acted up with inconsistent idle speed (no code). You can try carefully taking it out and cleaning it with a carb-throttle body cleaner. Also take care to clean the throttle body passages. I carefully used paper towels and wore nitrile gloves. A new one may be rather expensive so if it comes to trying a different one you might be able to get a newer one from a junkyard or internet cheaper. I have an '04 and they were used through this year here (on non-turbos).


O2 sensor may be good to replace if more than say 75,000 miles on it. They're usually good to 100,000 but some recommend 50,000 replacement (usually aftermarket manufacturers).

If higher mileage or if frequently driven with less than 1/4 tank of gas in it the fuel pump may be worn out. Not sure how much that would effect pressure versus volume of gas pumped.

Have you checked compression to rule out mechanical problems with sealing (valves, rings, gaskets, etc.)?

On 2.5 2000 Foresters I had previously the computer correctly identified bad knock sensor and crank timing sensor and threw codes.

I'm not sure about sensors there - MAP (manifold absolute pressure) or MAF (mass air flow, would be in air intake ductwork). I don't think my 2000s had either. My 2004 has a MAP sensor in the front side of the air cleaner box.
 

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1998 Forester, 2.0 awd
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8 Posts
Discussion Starter #8
Thanks for the replies so far.
Haven't put a compression gauge on to test the motor but it runs fine apart from the acceleration problem. Plugs that I replaced were the nice tan colour with no sooty or oily deposits. Motor makes no unusual noises or doesn't smoke.
How hard is it to remove the O2 sensor? it looks like it could be quite differcult. looks like it is rusted in from time and heat.
Cheers.
 

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1998 Forester
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39 Posts
O2 sensor removal

The trick to removing an O2 sensor, especially an old one, is patience, patience, patience. You will need a torch that can throw enough heat to make the metal cherry or red hot, a closed wrench (box-end, box socket) that fits the hex perfectly, a wire brush to clean off the rust and some fiddle tools like a dentist's pick and needle nose pliers.

First off, clean up the rusty hex and area surrounding the O2 sensor. Disconnect the wiring harness and slip the wrench onto the O2 sensor hex. Make sure it fits securely. Important! Then heat up the area around the sensor mount hole on the manifold or exhaust pipe with the torch until it is cherry red. Apply a bit of force on the wrench from time to time to see if it turns. If not, continue heating until it does. A light tap on the wrench will help but be cautious as you can damage the threads on the hole.

Let things cool down once you have the old O2 sensor out. Compare the plastic connector housings and make sure they are the same. I bought an after market OEM fit unit that didn't, so utilizing the dental pick and pliers, I was able to extract the contacts from the new unit and substitute the old plastic connector housing for a perfect fit.

Installation is straight forward. Make sure there is anti seize grease on the threads. I use a copper based type. Also make sure that the wire harness is routed away from the exhaust as it tends to melt the insulation and is secure enough that it doesn't get snagged on anything but loose enough so that it can move with the exhaust and engine vibration.

Good luck.
 

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04 Forester X, MT
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1,039 Posts
I also started a few days in advance putting some PB Blaster on the threads in hopes it would soak in good. I think it helped. On a 2000, one I removed without heat took out maybe 1 thread from the bung but there was still a couple left that held the new one. I agree it is a little risky. I am told some muffler shops can weld a new one in if it is too far gone but I have never actually checked. You may want to verify before you start.

The connector is a little different from many. It has to be rotated to unsnap before pulling apart. If your 98 is like my 2000s there is a plastic-coated metal tie-wrap kind of retainer where the wire is routed around the front axle. It would not be good for it to tangle!

Not sure if the supporting vendors ship there or not. I would pay the $ and get OEM from an online dealer vendor to save some $ for the front O2 (A/F) sensor. I have used a Denso replacement in the past for the rear O2 sensor that seemed to work acceptably and was plug-n-play with no rewiring required.
 

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1998 Forester, 2.0 awd
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8 Posts
Discussion Starter #11
I've been checking prices from our local dealer for a new O2 sensor and they want $670NZ, seems a bit steep.
On ebay they are going quite cheap - are they any good and are they compatable? My one is a 3 wire type - the car only has 1.
Does any one know what type the sensors are zirconia, planar or titania?
Cheers.
 

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I've bought several O2 sensors on ebay for different cars and never had a problem. Different vendors, but similar products. The 3-wire is available.

good luck
 

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1998 Forester
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213 Posts
My Forester just set a code for the front o2 yesterday I ordered one of the 3-wires from ebay I hope it works. If not I will only be out 22.00.
 

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1998 Forester, 2.0 awd
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8 Posts
Discussion Starter #14
Thanks for the replies, have ordered an O2 sensor off ebay for $39NZ should get it in about 10 days from the UK. Big difference to the $670NZ ($470 US) for the dealer part, fingers crossed that it is the problem.
Thanks.
 

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1998 Forester, 2.0 awd
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Discussion Starter #16
Haven't received mine yet but will let you know. Hopefully should receive it by the weekend.
 

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1998 Forester
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213 Posts
I installed my ebay 3 wire sensor today. Drove 38 miles home on it seems to run better than before. I hope I can get a couple more miles per gallon I'm at 22.5 the last 2 tanks of fuel.
 

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1998 Forester, 2.0 awd
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Discussion Starter #18
Got mine today and installed it after a battle - removed the exhaust to get it out. Doesn't seem to have made a difference, still hesitates, not a lot but enough to be anoying.
Now I'm stumped.
 

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1998 Forester, 2.0 awd
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8 Posts
Discussion Starter #20
No I didn't reset the ECU, thought about that later. Didn't get the car back together till 10.30pm last night.
What is the easiest way to reset the ECU?. is it just the normal disconnect the battery or is there a better way?
And do I just start and run as normal afterwards or is there a procedure to go through?
Cheers.
 
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