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Really need some help. Intermittent problem with electronic throttle not responding. Often I stop at a red light, etc. & then when I step on accelerator the engine doesn't rev normally. It has loping idle between 800 & 1000 rpm. When I step on gas pedal engine slowly revs up to around 1500 rpm. Check engine light comes on & cruise control light flashes. I have pulled two error codes: P2109 "Throttle /Pedal Position Sensor A Minimum Stop Performance" & P0638 "Throttle Actuator Control Range / Performance (Bank 1).

After I shut off the engine & turn it back on a few times, it revs normally. Then it often drives fine for a day or two. I don't own a WRX (I wish I did!) but I believe my '05 Subaru Forester 2.5X (normally aspirated,no mods) has the same "throttle-by-wire" system as the WRX& you guys are often very help on tech stuff.

Any recomendations on where to start? Throttle position sensor & throttle body appear to be one unit & sell new for $570ish. I was planning to take it off intake manifold & clean everything (I have new gasket). Mabe try to clean sensors on throttle & pedal with electric contact cleaner spray?

Any help is really appreciated!
 

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Hey there! Unfortunately, I've had this problem a few times, perhaps I could offer some insight after learning from my experiences.


For 2109 theres a few things you could check:
The electronic throttle relay
the gas pedal (Theres a stopper under it that if it is missing would cause the code)
the wiring (check for frayed/exposed/crushed/vampire tapped wires around the ECU or in the engine bay harness as the DBW system is VERY picky to voltage shifts. I had eletrical tape go bad on a splice and it caused the p2109)
the connectors
check ground wires
the ECU (last resort/rare)
and the throttle body.

A lot of older cars that had things like utec piggybacks/eletronic boost controllers/etc had a lot of splicing and what not so theres a greater chance of wire issues.
Also if you do use throttle body cleaner on a DBW throttle body, Ive heard that you need to use very little as too much can supposedly kill the sensor, fly/drive by wire systems dont seem to enjoy TB cleaners much...

If your really handy with a mutli-meter this could be relatively easy for you, if not try to find someone who is. I Can post the step by step diagnosis from alldata for the codes if you wish.

Basically the failsafe invoked in for this code fixes the eletronic throttle body to an opening angle of 15 degrees, so you will esentially need a tow home if you cant wipe the code by other means.

Best of luck! This code is a bugger, the fail safe invoked makes it all the more frustrating

Also, do you just have p2109 or do you have any others?
 

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Sorry. The site just truncated my lengthy reply to 2 lines. Lessons learned from P2109 that can "sneak up" after a battery disconnect or code erase. Adaptive learning may keep an "out of spec" sensor working fine until a code erase defaults back to factory specs. Then,BOOM, you are in limp-home with a code that won't go away because it resets in 80 ms after erase (and makes your Cruise light blink, to boot). This code can be set by either the Throttle Position Sensors (redundant pair of them) in the throttle body or those on the gas pedal. Some probing with a voltmeter will tell you which is at fault. (Check 2007 Legacy shop manual page EN(H4SO)(diag)-18 for spec voltages at closed throttle.) In my case the throttle body sensor had crept out of spec after 294k miles and a fraction of a turn of the 2 mm allen screw on the top of the assembly (and buried in epoxy threadlock) cured everything. (It is easier to buy a new throttle body than to remove the threadlock.)
 

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Hey there! Unfortunately, I've had this problem a few times, perhaps I could offer some insight after learning from my experiences.


For 2109 theres a few things you could check:
The electronic throttle relay
the gas pedal (Theres a stopper under it that if it is missing would cause the code)
the wiring (check for frayed/exposed/crushed/vampire tapped wires around the ECU or in the engine bay harness as the DBW system is VERY picky to voltage shifts. I had eletrical tape go bad on a splice and it caused the p2109)
the connectors
check ground wires
the ECU (last resort/rare)
and the throttle body.

A lot of older cars that had things like utec piggybacks/eletronic boost controllers/etc had a lot of splicing and what not so theres a greater chance of wire issues.
Also if you do use throttle body cleaner on a DBW throttle body, Ive heard that you need to use very little as too much can supposedly kill the sensor, fly/drive by wire systems dont seem to enjoy TB cleaners much...

If your really handy with a mutli-meter this could be relatively easy for you, if not try to find someone who is. I Can post the step by step diagnosis from alldata for the codes if you wish.

Basically the failsafe invoked in for this code fixes the eletronic throttle body to an opening angle of 15 degrees, so you will esentially need a tow home if you cant wipe the code by other means.

Best of luck! This code is a bugger, the fail safe invoked makes it all the more frustrating

Also, do you just have p2109 or do you have any others?
 
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