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Howdy! So I have a 2017 Impreza sport, and I put about 80,000 miles on it in a year commuting to a job. I moved way closer to work, but after about 2 months of city driving instead of highway, my RPMs started dipping form the normal 700-900 to just above 500. The only thing I have traced the issue to is when I push all the way down on the break pedal my rpms dip, but when i let off it just a little, my rpms come back up. Maybe it has something to do with the push to start? It even stalled out on me in an intersection, and it's an automatic. Ive gotten an oil change, replaced all the spark plugs and replaced the air filter. The dealerships I went to said that someone over filled my oil when they were replacing it and thats why I initially replaced the spark plugs. It's not a head gasket issue so I'm thinking its either the idle fuel valve or the MAF. Its nerve racking when im in traffic and my rpms dip and the whole car starts shaking. It also doesn't pick up the way it used to when I first got it. I am just at a loss and if its something super easy to fix let me know because car hunting in this market is just atrocious.
 

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Hello there. I just read this. That is not a fun happening with your Impreza.

I was thinking one of the sensors could be shot but…I noticed your "80,000 miles" point. Have you had your intake valve carbon cleaning done? The idle problem could be because of the caked intake valves.

If valves are clean, then maybe an idle relearn could do the trick?

If anyone else has ideas, please jump in. I am still learning about cars in general, and what I suggested are based off of the most common Impreza problems. Curious to know your actual solution.
 

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2017 Subaru Impreza Sport
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I too was going to ask if he ever had his valves and injectors clean. I use LiquiMoly to clean both Injectors and valves. I alternate between the two products every two fill ups. I know my car doesn't have 80k on it and I am using those products as preventive maintenance.
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I too was going to ask if he ever had his valves and injectors clean. I use LiquiMoly to clean both Injectors and valves. I alternate between the two products every two fill ups. I know my car doesn't have 80k on it and I am using those products as preventive maintenance. View attachment 29075 View attachment 29076
I know I have to do some carbon cleaning soon because I haven't done any preventative measures with 34k miles on the clock. Has LiquiMoly been working out for you?
 

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I know I have to do some carbon cleaning soon because I haven't done any preventative measures with 34k miles on the clock. Has LiquiMoly been working out for you?
It's too soon to tell. All I know is that is starts up and runs smooth. I don't have any rough idle or unnatural drop of RPMs but then again I have the manual. I am pretty sure the products I have been using are working as advertised. Also I see engine oil additive from Liqui Moly, which I put in after my first oil change and then again just this last oil change at just shy of 30k.
 

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I too was going to ask if he ever had his valves and injectors clean. I use LiquiMoly to clean both Injectors and valves. I alternate between the two products every two fill ups. I know my car doesn't have 80k on it and I am using those products as preventive maintenance. View attachment 29075 View attachment 29076
Keep in mind that our cars have direct injection. That Liquid Moly will clean the injectors and the exhaust valve, but not the intake valve....
 

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Keep in mind that our cars have direct injection. That Liquid Moly will clean the injectors and the exhaust valve, but not the intake valve....
I see and shouldn't be a issue since the top part of the intake valve won't be exposed to the gas when they are closed. Only the bottle part facing inside the chamber will have contact with gas and in turn be treated with the additive and remain clean. That is my logic towards that.
 

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2022 Sport 5-Door
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I see and shouldn't be a issue since the top part of the intake valve won't be exposed to the gas when they are closed. Only the bottle part facing inside the chamber will have contact with gas and in turn be treated with the additive and remain clean. That is my logic towards that.
Ideally in a port-injected car you would have the injectors clean the top of the valve, and especially the valve seat. The cleaner in a direct injected engine won't reach the valve seal, nor the runner where it can restrict flow of the air. Hence why Subaru makes a cleaner and tool for doing the top engine cleaning (intake valves and runners). It would reach what the liquidmoly can't.
 

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Ideally in a port-injected car you would have the injectors clean the top of the valve, and especially the valve seat. The cleaner in a direct injected engine won't reach the valve seal, nor the runner where it can restrict flow of the air. Hence why Subaru makes a cleaner and tool for doing the top engine cleaning (intake valves and runners). It would reach what the liquidmoly can't.
Thank you for that information.
 

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Here's a YouTube video showing how to use Subaru's maintenance kit which only costs less than $30. It's got all the product information in the video description also. I did my 2017 at 80K just a few months ago and the throttle assembly really wasn't that dirty, but it felt good to get this done. It smoothed out some of the rough engine idling, but changing the spark plugs made a bigger difference.
 

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I see and shouldn't be a issue since the top part of the intake valve won't be exposed to the gas when they are closed. Only the bottle part facing inside the chamber will have contact with gas and in turn be treated with the additive and remain clean. That is my logic towards that.
the intake valves get gummed up because of the EGR it brings the carbon that will deposit on them.
 
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