Rough rich idle and can not catch its self after rev

Irishtoaster

Irishtoaster

Member
Hi All,

The car is a 2001 forester st/b sti with an ej205 looks to be similar to 1999 Impreza After replacing half the cars sensors it feels like it is still idling roughly. when hot if you pull the vacuum line from the blow off valve it will idle much more steadily and not as rich. Here's the logs for the running normally
Screenshot_20221113-161401.jpgScreenshot_20221113-154918.jpg
Link for video of it running with vacuum lines and warmed up
https://imgur.com/a/p2p5fOm
and link for video of warm but with one vacuum line unplugged when checked it was at 700+ revs
https://imgur.com/a/40sRtMo
So far i have checked: Coil pack, Spark plugs, MAF, o2 sensor, corrected throttle position sensor, Checked injectors, New fuel regulator and filter. I did notice that during first start when cold it will raise the revs only for a minute and then instantly go to 500-600. It also struggles to catch its self after revving to about 2-3k

Its come a long way but still not fixed and I've ran out of ideas tomorrow I will try clean the iac but I doubt it will help. The day before we adjusted the throttle position sensor unplugging it made the car idle perfectly if that is any help

Sorry for my formatting
 
oh right so it could be a vacuum leak? ill try smoke it through the break booster and see if that shows anything. We did it through the intake before
 
So what happened for this to start ? Was it out of the blue or was it getting slowly worse over a while. ?
 
It’s being very slowly getting worst over a long time. When it first got worst it was very bad. It was idling at 100 and super rich. We thought it was maf and iac related
 
yep i tried a spare one i had. it had a different part number than the stock one but it fit and it made no changes. I did find a little vacuum leak with the blow off valve but fixing it didn't help too much. When its warm it will idle around 700 and run rich and then it will correct to a little higher and sound much better but then goes back to rich again after a few seconds. when cold it goes between 1k and 1.5k revs bouncing up and down
 
Vf34. Manual boost controller and no remap ?
. So it has always being missing since you bought it and is getting worse now , as it was running perfect and is suddenly Doing this .
 
Yeah, I took off the manual boost controller as the solenoid broke so its back to stock. It was ok in January to march with a bit of an idle issue but a new Maf got rid of it for a while. Then it got really bad after that so i started doing all this work. The issue looks like its just not adding enough air to the fuel its dumping in. last year though it ran like a gem with the manual boost controller and bigger turbo. I have been meaning to get a tune but i don't think there's any point until its running ok and not rich all the time. Is there any test i can do that can show if its a sensor? I unplug the maf and the car dies straight away. I checked the fuel pressure gauge and with this its not steady like it shakes violently between 41-45 psi but i just replaced the regulator and pump
 
did You buy this about 2 years ago or so having had a manual swop done and advertised as not running right ?,
I remember there was one for sale D18 area that seems similar
Could be anything really,get someone to look at it who knows them inside out would be the cheapest option rather than lashing more parts at it would be my 2 cents
Fitting a different turbo and not maping it is probably the answer if it wasnt already there before that was fitted I would guess
Hope You get sorted anyway :thumbsup:
 
Ye it’s really hard to know really with out standing in front of it and doing a few tests .
Sounds like your after changing a lot and still no joy
 
Yep that was this car. we bought it and then spent a good few months replacing parts that needed it (Coilovers, turbo, exhaust). Also way to much research into these Japanese ecus and the lack of documentation. Would there be any one you could recommend for this in the Dublin area? I have already gone to one specialist but he gave up on it. I cleaned the Pressure exchange solenoid today and it now runs ok still rich and a bit limpy but it catches its self now and wont die on idle meaning i can finally drive it to someone if needed. Yep we did a compression test all 4 are good and inside the tolerances PXL_20220418_154215074~2.jpgPXL_20220418_155318463~2.jpgPXL_20220418_154608018~2.jpgPXL_20220418_154959180~2.jpg
 
See your black and white connectors on the coil packs , black ones need to be connected to the rear most cylinders on both banks .

I did see a legacy once with a bad earth on the alternator once that ran bad , the alternator doesn’t have a dedicated earth , it earths through the ac bracket , we had to remove this and sand down the contact points on the alternator and the bracket and that sorted it, was very strange and we were clutching at straws at that point
 
Oh right i had a look at the ground for the alternator and it did look a bit dirty ill try sand it down a little. Il try that coil pack thing as well. We got the Subaru dealership reader there so hopefully it helps to look at trims and all. Disconnecting the Throttle position sensor makes it idle pretty good but looking at the fuel correction it goes straight to -25 oddly so maybe we need to adjust it againScreenshot_20221116-164558.jpg
 
What should the throttle position sensor voltage be at idle ?
Doesn’t look right anyway to me
 
according to service manuals its about 0.3 volts and with the new subaru reader i can see its wayy to high, It says its running at 0.48v and will go up to 3.38v with the throttle flat. I ran it there but i will check again and oddly the neutral signal was not getting activated with the car in neutral but that may be grasping at straws.IMG_0330.JPEGIMG_0331.JPEG
 
ok perfect great. Would a stuck open/closed Vapor Canister Purge Solenoid cause bad idles and running super rich? Its the only part left of the fuel system that i haven't looked at
 
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