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major hesitation on low revs


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hello all need some help if anyone can


i got a my98 wrx jdm


had recent rebuild engine works perfect the problem got is when intial pull off from 1k revs to 2k revs jumps and kangeroos like a really bad misfire, after 2k-2.5k revs it feels good under boost, fromcold it runs low idle and lumpy,when hot tends to settle down,hoping someone got some ideas


work done


new irridium plugs and leads

newfilters all round

checked allboost pipes are in correct postion (3 port solinoid)

no vacum leaks or boost leaks

checked all intercooler/turbo pipes

disconnected maf engine cuts outs

dsconnected lambda sensor has no change still does same


wondering if anyone nows what to check next thanks

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everything is totally standard, basically bought the car last month with no.3 knocking, so new rebuilt engine everything has been plumbed in correctly no leaks or plus loose,been double checking everything ova and ova.

on the 3 port solinoid ive left the bottom hose to vent and blanked off the pre turbopipe it slightly improved but still there on verylow revs

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Have you done a classic self ecu code check ?

Maybe Check the plugs to the tps and icv maybe give the icv a clean as well

I don't think a v4 jdm wrx is supposed to have a 3 port boost solinoid and I just did a quick Google and come up with this

MY98 WRX (JDM) ... 2 port solenoid 0.9mm restrictor fitted between the turbo and the tee piece

I only mentioned the solinoid as to change from 2 port to 3 port requires a map tweek.

Symptoms do sound like a possible air leak from the inlet but start with the ecu Check as it could be something totally different

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Well throttle body has been replaced, so no leaks so that's that sorted but still same no difference, still hesitates, lumpy when cold start, when hot idle levels out and not so lumpy, sometimes when pull up to junction revs hold to about 1200rpm for 5-8 seconds then slowly drops back to normal, when turn car off then go to restart it idles lumpy and really low revs like ready to cut out then picks back up after about 3-5 seconds, checked everything possible, boost on idle sits at 0.6 then when fully boost goes just above the 1.0 on my gauge. Any body got any thoughts where to go next

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Have you done a classic self code check? If not there's a how 2 in the tech section on here

Have you tried cleaning the idle control valve and checked that the little gauze filter isn't perished?

If it's not been remapped it should only boost to 0.7 bar ish ,so it's over boosting a bit .

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Yeh I've done that comes up with no faults just constant flashing, I've reset ecu, cleaned the icv the orange gauze is like new all cleaned as well, there's no remap or mods everything is standard, I got a hks gauge u saying that when I checked sometimes it went just below the 1 then in ova gears it went rite up to the 1.0 bar and slightly ova, if it's ova boosting any ideas wot the likely cause could be thanks

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Over boosting is usually caused by someone fitting mods that let the turbo spool more freely (Decat downpipe, cone filter ect...) but it can also be caused by vacuum ,boost solinoid, actuator or map issues .

Sounds like your best bet is (as tidgy said) to check your timing marks and get it on a dyno .

As a decent dyno operator might be able to diagnose the issue and save you spending a small fortune on random parts trying to stumble across the fault .

You don't want to be giving it full boost until you know your afr is correct cos if it runs lean it will go bang again [emoji53]

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  • 5 years later...

I am driving a Subaru Impreza 5Door 1.5R 2009. Recently when I drive on the high way at 2,000RPM and try to over take others vehicles, So I accelerate, The RPM will jump up to 5,500rpm. But Now it will cut off at 4,000 rpm or 3,000rpm. 

If at 5,500rpm that's mean my fuel consumption will be at 11.5km per liter, But if it's at 3,000rpm that my fuel consumption will drop to 6km per liter. 

Can anyone experience it? why? ? is the injection issues?

Once drop till 3,000-4,000rpm it is very difficult to go back to 5,000rpm until now my car still at 4,000rpm or below. 

It can be ram up to 4,000rpm but it take more time like another 3-6 sec . 

any one know what happen?



Edited by Robin Koh
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