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Old 12-22-2017, 01:05 PM   #1
SurfPine
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Default 2.5L Throttle "runaway" acceleration Drive By Wire DBW

My daughter's car, 2005 Forester X with the naturally aspirated 2.5L and manual transmission, has started to experience a "runaway" throttle situation after it has started to get cold out.

The car has been grounded until this gets figured out. I drove it last night, temp outside roughly 12f, and at first, I thought I accidentally had my foot on both the brake and throttle as I witnessed the RPMs going up while I was braking with the clutch pressed in. I didn't think much of it until roughly 2 hours later when I went to pick her up and the same issue occurred, now about 10f out, braking with clutch pressed in and RPMs surged to 5500 RPMs. I blipped the throttle twice and then the RPMs returned back to "normal" for 5 seconds or so, then RPMs started going back up but only to about 2500 RPMs. Blipped throttle again and then went back to normal RPMs. I experienced multiple similar throttle situations on the short drive back home.

I do understand this is supposed to be a drive-by-wire throttle, so we are not talking about the potential for a throttle binding up because of a cable being cold with lack of grease. I've tried doing some online research and have found some similarly reported situations but most seem to center around throttle "surging" issues, meaning the throttle more pulses at a higher than normal RPMs but doesn't fit the description I am experiencing of a "runaway" throttle going to redline.

Anyway, the info I've found that doesn't quite match addresses changing the TPS or O2 sensor or even spraying WD40 on the throttle body near a spring. Some or the majority of those instances are for forced induction. Some other info found mentions flashing the ECU but those are all forced induction where the owner has tuned mapping on their ECU.

I just went to check for codes with my Scanguage II and no codes have been thrown. No reset has been performed, e.g. ground has not been removed from the battery.

I'm a bit stuck at the moment but may have to bite the bullet and have a Subaru mechanic take a look but I'm not willing to accept them just throwing parts at it to see what sticks.

Any help or ideas will be very appreciated. Thanks.
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Last edited by SurfPine; 12-22-2017 at 03:00 PM. Reason: Changed title to be more descriptive as DBW assemblies are bound to fail
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Old 12-22-2017, 02:53 PM   #2
SurfPine
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Default

UPDATE: I also posted on reddit and a user on there linked me to this video -


I didn't have any Electronics Contact Cleaner but found ECC is made up from isopropyl alcohol and air. So I took some isopropyl alcohol and put it in a spray bottle and sprayed the accelerator in the area where the connections are, where it pivots. The runaway throttle acceleration has not surfaced once since spraying the isopropyl alcohol in there. Immediately preceding spraying the isopropyl alcohol, the runaway throttle acceleration was happening a lot. I'm 100% convinced that accelerator assembly needs replaced and I am going to source it and get it ordered.

Last edited by SurfPine; 12-22-2017 at 04:43 PM. Reason: speeling
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Old 12-22-2017, 06:35 PM   #3
v2rocket_aka944
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Default

it could certainly be a screwy sensor on the pedal assembly but i can't help but wonder if the age/mileage of the throttle body combined with the low temperature is making the throttle motor mechanism stick like you mentioned (not a cable, but the actual motor/drive gears).

even a low throttle angle (cruising throttle) will make the rpm shoot up when the load is taken off (shift into neutral)
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Old 12-23-2017, 08:58 AM   #4
SurfPine
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You do mention a valid point as the car is a 2005 MY and has 147k miles. I appreciate your input.

Prior to me spraying the isopropyl alcohol on the throttle assembly, the car was having the runaway throttle issue almost continually. Since the temps had "warmed" up to 28f, I had taken the car out to verify if the runaway throttle issue was still going to happen, and it did but to a point where before I pulled into my driveway, I had to just about coast in while I kept blipping the throttle, to keep the engine from revving so high, redline. I probably had to blip the throttle 5 times within 100 yards. I then only sprayed the isopropyl alcohol on the pedal/throttle assembly. I again went for a test drive and no runaway throttle issue. The runaway throttle issue has not occurred once since I sprayed the isopropyl alcohol. I even took the car out later in the day, which was approx. 4 hours later, and no runaway throttle issue. I am convinced I've isolated the issue to the throttle assembly and I ordered a new one.
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Old 07-26-2020, 12:09 AM   #5
wakaquick
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Thanks this helped me figure out why my old ETB was surging like that in the winter. I read it awhile back but haven't registrar till now better late than never at least.
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