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Hello everyone. I've been having an intermittent acceleration problem. I'll step on the gas and my car won't accelerate like it used to and then it will explode like a rocket. Sometimes it feels like the turbo or whatever isn't kicking in at all. The acceleration isn't constant. I'm thinking it's most likely a transmission issue or something to do with the turbo like the wastgate going out. Problem comes and goes. Any ideas? Car has 184k on it. Thanks.
 

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From a similar issue that I thought I may have (turns out i didnt), I did a LOT of forum searching and online research, one possible issue could be the 'mass airflow sensor (MAF)'. Something to do with it not getting the correct amount of air in at the right time, causing a surge. I'm no expert though, so I could be woefully incorrect.
 

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Hello everyone. I've been having an intermittent acceleration problem. I'll step on the gas and my car won't accelerate like it used to and then it will explode like a rocket. Sometimes it feels like the turbo or whatever isn't kicking in at all. The acceleration isn't constant. I'm thinking it's most likely a transmission issue or something to do with the turbo like the wastgate going out. Problem comes ad goes. Any ideas? Car has 184k on it. Thanks.
Check the basics. Disconnect and remove your MAF, clean it thoroughly with aerosol brake cleaner, replace, reconnect.

Check you air intake box, air filter, ducts. Any leaks? Filter okay?

Start a systematic check of all your vacuum hoses (and there are a bunch). If they are old, cracked, brittle, not sealing well (you'll know because they slip off easily), replace them. If possible, replace with reinforced fuel line. At your mileage, they all need replacing, no matter how they appear.

You have a turbo car, so there are several unique ducts under the intercooler which need checking. Clamps in place? Check the intercooler as well - clean inside? Any leaks? Remove the waste gate, clean, inspect, say a prayer, reinstall.

If you are still using your original TD04 turbo, you might want to remove and inspect it. It's really approaching end-of-life

Put a can of Seafoam in the gas tank. In one tank of gas, it will clean the fuel system and injectors. You can feed another can through the throttle body while the vehicle is running - a 'smoking' experience.

When did you last replace your front O2 sensor? Never? Look on eBay for the genuine Denso part - ~$65-80. Replace it. Don't even look back. Honestly, this replacement ought to be part of the 105k timing belt service.

Is it possible you got a bad tank of gas? Responsible gas stations keep their tanks clean, vacuumed, etc. plus there are final pump filters to catch any debris before it's pumped into your car. With not-so-responsible gas stations (can you spell 'Swifty'?) there's no telling what comes out of the pump. Your own fuel filter is supposed to catch stuff as well.

Buy a case of ATF HD from your Subie dealer. When the car is fully warmed, drain the transmission and replace the fluid. You will have to do this in three separate steps, separated by a few days each, to get 90% of the fluid changed. While you're at the dealer, buy a transmission filter (pricey). It's an easy replacement.

You car is drive by wire. It's possible the throttle position sensor is getting flaky, or possibly just gummed up. In an earlier step, when you had the intercooler off, look inside the throttle body. Clean? The home of several small animals? If the latter, you might remove and inspect the throttle body rather than just spraying inside with an aerosol. If you do remove the throttle body, be sure to coat the attachment bolts with anti-seize when you re-install them.

The solution may not be in the above steps. But, as you're doing the above, you're likely to stumble onto the problem. Good luck.
 

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Discussion Starter #6
Check the basics. Disconnect and remove your MAF, clean it thoroughly with aerosol brake cleaner, replace, reconnect.

Check you air intake box, air filter, ducts. Any leaks? Filter okay?

Start a systematic check of all your vacuum hoses (and there are a bunch). If they are old, cracked, brittle, not sealing well (you'll know because they slip off easily), replace them. If possible, replace with reinforced fuel line. At your mileage, they all need replacing, no matter how they appear.

You have a turbo car, so there are several unique ducts under the intercooler which need checking. Clamps in place? Check the intercooler as well - clean inside? Any leaks? Remove the waste gate, clean, inspect, say a prayer, reinstall.

If you are still using your original TD04 turbo, you might want to remove and inspect it. It's really approaching end-of-life

Put a can of Seafoam in the gas tank. In one tank of gas, it will clean the fuel system and injectors. You can feed another can through the throttle body while the vehicle is running - a 'smoking' experience.

When did you last replace your front O2 sensor? Never? Look on eBay for the genuine Denso part - ~$65-80. Replace it. Don't even look back. Honestly, this replacement ought to be part of the 105k timing belt service.

Is it possible you got a bad tank of gas? Responsible gas stations keep their tanks clean, vacuumed, etc. plus there are final pump filters to catch any debris before it's pumped into your car. With not-so-responsible gas stations (can you spell 'Swifty'?) there's no telling what comes out of the pump. Your own fuel filter is supposed to catch stuff as well.

Buy a case of ATF HD from your Subie dealer. When the car is fully warmed, drain the transmission and replace the fluid. You will have to do this in three separate steps, separated by a few days each, to get 90% of the fluid changed. While you're at the dealer, buy a transmission filter (pricey). It's an easy replacement.

You car is drive by wire. It's possible the throttle position sensor is getting flaky, or possibly just gummed up. In an earlier step, when you had the intercooler off, look inside the throttle body. Clean? The home of several small animals? If the latter, you might remove and inspect the throttle body rather than just spraying inside with an aerosol. If you do remove the throttle body, be sure to coat the attachment bolts with anti-seize when you re-install them.

The solution may not be in the above steps. But, as you're doing the above, you're likely to stumble onto the problem. Good luck.
Wow thanks for the lengthy response will check these things thanks!
 

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did you find a solution? i recently bought a 14 forester xt with 95k miles. i think i am getting a similar problem. when i accelerate from a stop. it seems to boggle or lag then it would be fine. occurs almost at every stop or very low speeds
 

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Do you have an auto or 5spd manual transmission? Reason I ask, if it’s 5spd, the clutch might be slipping depending on how many miles have been travelled. A worn clutch can lower how much boost your engine is getting.

My current clutch is going on it’s way out. Originally I went for a stage2 clutch, but then my engine build took a different turn and I’m making more power. Long story short, I was making 22lbs consistently, now the stars have to be aligned just right and I might see 19lbs.
 

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Do you have an auto or 5spd manual transmission? Reason I ask, if it’s 5spd, the clutch might be slipping depending on how many miles have been travelled. A worn clutch can lower how much boost your engine is getting.

My current clutch is going on it’s way out. Originally I went for a stage2 clutch, but then my engine build took a different turn and I’m making more power. Long story short, I was making 22lbs consistently, now the stars have to be aligned just right and I might see 19lbs.
its an auto. with the cvt transmission.
 
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