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Rough Idle


Sonic11
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Right guys, im a newbie! Literally joined 5 minutes ago! The scoob ive got now is a Subaru Impreza turbo 2000 and its my first ever scoob. 

The issue I DID have was the sensation of the revs hitting the limiter at only 4500rpm! I then got a new MAF and this problem was solved, it now pulls like a train. The NEW problem now is it has rough idle, the revs keep on fluctuating between 300rpm to just over 1000rpm. It sometimes stalls at traffic lights....the other issues is when the car drops to about 300rpm and is about to stall (when im standing by the back of the car) i can see a hint of black smoke? And it is smelling a bit oily? :( Any help would very much be appreciated.

 

Before replacing the MAF i replaced plugs (gapped them to 0.7mm) and leads.

Thanks

Cai  

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Hi mate sounds exactly like the MAF again to me Did you buy it new ?

But from what people have changed before in the past or has caused the same problems 

 

  • Low 95 Ron Fuel 
  • Cone filter (killing the Maf Sensor if it's oiled)
  • dump valve (some subaru engines just don't like them)
  • Spark Plugs ( Wrong gaps would cause it too)
  • IAC (Idle Air Control Valve)
  • TPS (throttle position sensor)
  • Split pipes/vacuum hoses or loose (check them with some warm soapy water with a water sprayer)
  • throttle body ( Gets gunked up, just needs a clean) 
  • 02 Sensor/Lambda Sensor

 

Thats all I can think of at the minute mate I would maybe look at the plugs check that its the right gap. I would always start with the cheaper options 1st have you checked at all for any codes and cleared them from the bad maf before ?

 

Oh and welcome to S.O.C feel free to have a look around and join in good bunch of Ladies and Gentlemen if you can call-em that on here ;)

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Hi and welcome,

Try reading your fault codes. That should point you in the right direction.

Here's a how to guide

http://uk.subaruownersclub.com/forums/topic/2366-manually-reading-ecu-codes/

My guess is the O2, aka lambda sensor but the codes will reveal all. You may have to do a reset first, then drive the car again before check for codes again. Reason is, it will store the code so when the MAF threw a wobbly, the code will still be in there, until it's reset.

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Hey guys, thanks for the replies! Ive highlighted what i have and havent done from gambits list below:

 

  • Low 95 Ron Fuel - I doubt its this as ive filled up in a few stations over the past month. 
  • Cone filter (killing the Maf Sensor if it's oiled) - Replaced this with standard box this morning! 
  • dump valve (some subaru engines just don't like them) - I have standard dump valve fitted!
  • Spark Plugs ( Wrong gaps would cause it too) - Checked gaps a month ago, but will check again. 
  • IAC (Idle Air Control Valve) - I havent checked this, is there a way to test it??
  • TPS (throttle position sensor) - I havent checked this, is there a way to test it??
  • Split pipes/vacuum hoses or loose (check them with some warm soapy water with a water sprayer) - I have attempted this and saw no sign of leaks, are there any hidden ones that arent so obvious?
  • throttle body ( Gets gunked up, just needs a clean) - I'll give this a clean in the next few days.
  • 02 Sensor/Lambda Sensor - I'll try and find a replacement. Does anyone have a spare one going? 

 

What immediately sticks out to me from what you guys have said is clearing the codes from the faulty MAF before. I Havent done this at all. When i fitted my new MAF i did disconnect the Battery over night, but im guessing thats not the right way to go about it?  

 

If anyone knows anyone selling a Lambda sensor let me know, it will be worth replacing. 

Thanks for the replies, i should have joined months ago!!! 

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Thanks for the welcome tom!

Bit of a plot twist now tho, i just drove to work with the standard airbox fitted and now the car runs even worse?! feels like its hitting the limiter and has really bad idle!! Top end was fine yesterday with cone filter fitted?!

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Was the Maf new mate seems strange that changing that has made it worse. Would, make me want to look closer to the maf and the intake pipes a bit more for damage or splits. 

Have you pulled the Maf plug off while the engine is running ? it should stall out if it doesn't sure sign it's dead. I had the same problem when I bought a 2nd hand one from a breakers it was toast they don't take much to brake. and if you're cone induction kit was an oiled based one I would almost put money on it that being what killed the 2nd MAF 

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With what you have done, it sounds like MAF, although its just guess work. Checking the codes takes moments and is an easy job. It will also give you the answer you need.

 

Taking the Battery off overnight will clear the codes so you shouldnt have any stored from before the original maf was replaced.

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Hey guys, rthe codes that came up were 23 & 24. Idle circuit and MAF. The codes kept on going round, as in 23,24,23,24,23,24. I think i timed the pulses right plus the errors that came up are what i expected so i must have done it right. 

 

What i will admit about my MAF is that i bought it off eBay.....new.....but only cost me £50....I dont think it was a genuine OEM part but the part numbers matched. Yes yes i know.....i shouldve dished out the an extra £50. haha. 

 

AND....i just unplugged the MAF whilst is was running and, yep, you guessed it, it kept running. :( 

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I won't judge anyone for trying to save a few quid mate, I have done it myself once with a MAF and I did it more recent with a Hub :( put the hub on thought it was just a dry bearing as it made a noise but had no movement in the wheel so had another bearing fitted was fine for awhile so wasn't until I went to have another one fitted was told the hub was again chewing the bearings up :(  anyway less of my problems :) my list is long at this moment in time but hopefully be sorted any day now.

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Ok update time, so i fitted the standard airbox and the car was running worse! I then cleared the ECU with any errors following the link gambit shared! Tried putting my foot down again.....car still idles terrible & gives the impression your hittting the limiter at 3500rpm?! 

 

So i then put the cone filter back on and the car now pulls like a train again?!! (still has bad idle) So its safe to say i am completely mind !Removed! and im looking forward to 'getting on the beers' tonight!

 

If anyone has an idea whats up with it please let me know! haha 

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If the smoke is black it's probably unburnt fuel if it's greyish blue then that would indicate it's burning oil .

The 3.5 k limiter sounds like "fuel cut " like a sort of limp mode normally associated with overboosting , knock or stored engine codes .

Has it got a dump valve if so try blanking it off to make sure it's not faulty . Double check any plugs injectors, sensors, ht leads ect .

Sent from my GT-I9300 using Tapatalk

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