2006 Impreza EJ201 Flat spot at 1750rpm when accelerating

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frustrated
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2006 Impreza EJ201 Flat spot at 1750rpm when accelerating

Post by frustrated » Sun Nov 08, 2020 2:54 pm

Hello,

2006 Impreza wagon non turbo EJ201 250,000km on the clock.

“Flat” spot at 1750rpm under load
Gutless up hills
Cruise through a roundabout and go to accelerate out - flat spot 1750rpm
Take off at traffic lights - flat spot 1750rpm
Up a steepish incline on a long driveway - flat spot 1750rpm
Take off on the flat - flat spot at 1750rpm
Floor it to get past the flat spot and it eventually jumps to 3000rpm - no in between.
Accelerate quickly when not under load and it sounds like it is gasping for air.

Sitting still with no load, accelerates through the 1750-2000rpm range with a bit of roughness felt through the floor panels, not felt outside that range, but doesn't 'die' like it does under load.

6 months ago:
Scanned O2 sensor bank 1 sensor 1 error. Sensor replaced. Battery disconnected and brake pedal depressed for 10 seconds for computer reset. Ran better for a week then back to the same issues.

Now:
Computer reset has no effect.
No error codes when scanned.
New air filter made no difference.
Catalytic converters in good condition.

Just wondering if anyone else has had this issue and what is the most likely cause?
MAF, plugs, leads, coil, fuel filter (in tank under the rear seat), something else?
Been to 3 mechanics and short of replacing the above items and it “might” fix it, no-one can give me a more specific answer.

Thank-you.

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El_Freddo
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Location: Benders (aka Bendigo) Vic

Re: 2006 Impreza EJ201 Flat spot at 1750rpm when accelerating

Post by El_Freddo » Sun Nov 08, 2020 5:29 pm

G’day frustrated,

Welcome to the forum - I can see why you’re frustrated!

Auto or manual?

One thing that comes to mind is the idle air control valve. Although it may not be open when coasting or under load, it could possibly have a dodgy seal that’s interrupting the air flow into the engine. Also check for vacuum leaks.

Another thought as I write this - variable valve timing and that idle butterfly device on this engine? If so, look into the idle butterfly device. It could be getting stuck, slow to open or not opening via the little servo motor properly.

Subarino had this issue with his GT foz over ten years ago, but I can’t remember the process they used to rectify the issue. I do know the intake manifold had to be removed. I can’t find the thread, but if I do I’ll post a link here.

If it has a MAF sensor and not a MAP sensor, clean the AFM or replace it with a known good one (borrow one if you can to diagnose the issue - then buy a known good one if that turns out to be the issue)

Threads that could be of interest:
2007 Impreza rev issue at around 2000rpm

2006 Liberty with no acceleration - egr issue apparently.

Any other unrelated issues - other things not working, blown tail light globe..? Any maintenance other than what’s already mentioned?

Cheers

Bennie
"The lounge room is not a workshop..."
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El Freddo's Pics - El_Freddo's youtube

frustrated
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Re: 2006 Impreza EJ201 Flat spot at 1750rpm when accelerating

Post by frustrated » Sun Nov 08, 2020 6:36 pm

Thanks Bennie

It's an auto.

I'll check out those links. The IAC valve is beyond my mechanical ability but I will mention it to a mechanic.
Pretty sure it's a MAF sensor Part number: 22680-AA360.
I had the same idea - go and find one that is ok and test it.

The only other 'fault' that I'm aware of currently is the CEL not working (never has since we've owned it). I suspect the previous owner or his dodgy mechanic found a way to disable it. But it wouldn't be on atm because there are no fault codes.
1 headlight blew about 7months ago. Oil change a few weeks ago. Top radiator hose replaced a few months ago. New radiator (but not hoses by the dodgy mechanic before we bought it 8 months ago).

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El_Freddo
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Re: 2006 Impreza EJ201 Flat spot at 1750rpm when accelerating

Post by El_Freddo » Sun Nov 08, 2020 8:26 pm

Yep, that’s an air flow meter of some sort. I thought Subaru stuck with the MAP since 1999/2000 with the Gen3 Liberty.

I don’t know if that can be cleaned like the older Hotwire style afm.

That unit isn’t a cheap part new. Subaru’s typically don’t like non genuine parts the newer they are. They’ll get by with aftermarket units but won’t be the best or they’ll be back in the workshop before long.

Cheers

Bennie
"The lounge room is not a workshop..."
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El Freddo's Pics - El_Freddo's youtube

frustrated
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Re: 2006 Impreza EJ201 Flat spot at 1750rpm when accelerating

Post by frustrated » Sun Nov 08, 2020 9:21 pm

The MAF appears to have ceramic diodes and is different to the wire one I watched on you-tube.
I also had to replace the air con tensioner pulley - the plastic one melted when the bearing seized.
Also drained and replaced the power steering fluid. It had what smelled like gear oil mixed into it and was overfull.

frustrated
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Joined: Sun Nov 08, 2020 6:40 am

Re: 2006 Impreza EJ201 Flat spot at 1750rpm when accelerating

Post by frustrated » Sun Nov 08, 2020 9:28 pm

Can't figure out how to post a pic. The diode things are inside and visible through the hole in the side.
Here's a link of one on ebay. Reasonable prices for ones from the wreckers, but no guarantees they will be any good.
https://www.ebay.com.au/itm/SUBARU-IMPR ... 3649661156

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