Hi Guys

 

I'm having a problem with my 2003 Subaru forester. When I push the accelerator to about 25% or 100% the car pulls well and accelerates at the normal rate. My problem comes when I accelerate at about 45% to 90% of the way. The car seems to loose power and seems to makes a slight jerking motion as if you were pumping the accelerator from 90% to 20%. I really need to find what is going wrong as it is killing me having to use 25% or 100%. I am fairly technically minded. 

 

Fuel filters are clean

Car has about 97 000km on the clock.

 

Any help is much appreciated guys

TPS check would be a good place to start.

knock sensor. Try premium fuel and see if that changes anything. By the mileage and age of the car, a failing knock sensor would be expected.

Edited September 23, 201411 yr by MilesFox

I borrowed my Brother's OBDII scanner. It's a Harbor Freight Cen-Tech. I don't think they're too expensive.

 

It's sure nice to plug it into the easily accessible plug and get a nearly instant read of any faulty codes. I don't know the limitations of the device, but when I got a "check engine" light, I plugged it in and it told me that one of the exhaust  sensors was faulty. 

 

If it it is a knock sensor as MilesFox suggests. I'd think it would throw that code.

 

Really nice feature of newer cars.

 

JW

Would the knock sensor bring on a check engine light? I don't have a check engine light. I have noticed on the higher rpm that there sometimes is a fast ticking sound, could that be it? How would you suggest that I check the sensor? 

because the knock sensor is supposed to signal the ECU to alter engine timing, many times the ECU cannot determine if it is receiving a true signal or not. Plenty of folks have had bad sensors with no code set. Visual inspection often shows the part to be cracked. There MAY be ohmmeter or oscilloscope tests that would help with diagnosis. But, many people just buy the $20 part and put it on. It's advised to note and duplicate the direction the cable points when removing the original and installing the new sensor so the new one isn't stressed. I THINK 17 ftlbs is correct torque - don't overtorque it either.

 

OBDII DTCs are nice to have - but they rarely point directly to a bad PART. Better to think of them as indicating a 'system' that seems to be supplying the ECU wit data outside of the allowed tolerances. Sometimes the sensor is fine and rodents have chewed wires, or alternators are bad, or connectors come loose, or batteries are weak, etc.

Thanks allot for the detailed explanation and for your time. Let me have a look at that this weekend and will get it replaced and will post an update on Monday to let you guys know what I discover and if we have sorted the issue. Your help is much appreciated guys.

Did you ever find any cause for the problem???

Still no fix yet, sorry. Had a look at the tap sensor and it seems to be fine :/ Still not sure what is wrong. Got a check engine light come on when pushing the car a bit on the weekend as I was late for a  meeting, but the light was on for 5min and then hasn't come on again. Will the system hold a log of errors so I can see what the old error message was?

Codes are stored for usually 80 drive cycles so the code should still be stored in the ECU.

 

Run it by an auto parts store. Most will scan codes for free.