Rough Idle but seemingly fine while driving?

[SUBRACY]

Hoping someone could impart some knowledge my way, Seemingly overnight last week my car developed a really rough idle not just on cold startup but whenever i come to a stop or clutch in, so much so that at time the idle will drop so far that it'll stall. Now i have a rubbish Bluetooth OBD adapter and the torque app that i used to pull a p0508 code from the ecu (P0508 - Idle control system circuit low input) i took the IACV off and thoroughly cleaned it and replaced the gasket, this did nothing to remedy the idle problem so i actually purchased a new IACV and gasket to try that out (wanted to fix it asap and on my own if possible), this also did not help at all.

now ive read that this can be attributed to a number of things including vac leaks and bad plugs / fuel filters etc, So i thought i would change the plugs and filter and see if this remedied the issue. to my dismay it did not help at all. next i pulled the throttle body off and cleaned it out (was filthy to say the least) also did nothing, and now i am feeling a little lost as to what it might be.

Can anyone shed some light as to what it could be? again the car seems to drive perfectly fine when under acceleration but when idling its very rough and when the Fans kick on it really struggles to keep idling.

Any help would be much appreciated!

oh btw the car is a 2003 wrx wagon

[Marky]

Does it have a venty blow off valve?

[SUBRACY]

Quick reply thanks! no it doesn't just the factory one, sorry shouldhave mentioned its practically stock apart from a farty exhaust tip

[Guest]

Would point finger at maf.

[SUBRACY]

I gave it a clean with maf cleaner as i though that might be the issue but did not help either! how would i diagnose a dead MAF? would this also throw the p0508 code?

[Joker]

sounds like its running on 3, hows the fuel consumption?

I knocked the plug off an injector once : had a mean as idle, seemed to run ok but drank like a fish

[Marky]

I'm in TGA too, I can swap out the MAF with you sometime if you want to test it

Can also do a leak test, sounds like a vacuum leak

[SUBRACY]

Just had a look and the plugs on the injectors are all plugged in.

Thanks Marky, I have a mate here who has a Bugeye ill see if i can borrow his to test out.

How is a leak test done? ive seen read that you need some sort of Smoke machine ?

is it dangerous to be driving around with the rough idle? (apart from the horrible mileage i seem to be getting)

Thanks for the Info guys this has been bugging me!

[Leufkax]

A stuffed MAF won't necessarily throw a code, had a similar experience recently

[Marky]

Nah, just block the intake and jam a compressor into a vacuum hose

It amazing how many cars have minor leaks, it's a two minute test to do (if you have a compressor anyway)

I wouldn't say it's dangerous as such, but it'd pay to be nice to the car till you find out the reason for it. Poor mileage also points towards a bad AFM or leak too

[Andy_Mac]

Thats my backyard solution, intake blocker and connection fitting all in one.

Would have sworn mine had a leak but got a smoke test done on it whilst up in auckland yesterday and absolutly nothing showed up.

[SUBRACY]

So all that's happening is your pressurizing the intake to listen for a hiss? ill have to make something similar with some PVC pipe from Bunnings and give it a go!

[Andy_Mac]

Basically yea. Doesn't always work but its certainly a start.

Just gotta make sure whatever you use is the same size as the intake pipe that it can be pushed in and tightened with the hose clamp.

[Subirex Automotive]

sorry to hijack a bit old thread but have you checked your vvt solenoid? the filters do break and gets stuck to the solenoid and advance the pulley timing sometimes to 50 degrees and gives the same symptoms as you are experiencing.

[KingCole]

I have the exact issue. I need to find someone who can help me out with a Vac/boost leak test around Auckland. I replaced the IACV gasket, the IACV itself and cleaned the MAF. Idle is still very low and rough. I got 140km from half a tank from normal driving so it is pretty bad haha. I do have a venty HKS SSQ BOV though.

[hijacka]

Moneys on afm too

[Marky]

 subirex said:

sorry to hijack a bit old thread but have you checked your vvt solenoid? the filters do break and gets stuck to the solenoid and advance the pulley timing sometimes to 50 degrees and gives the same symptoms as you are experiencing.

Ooh that is a thing too isn't it

[Subirex Automotive]

 KingCole said:

I have the exact issue. I need to find someone who can help me out with a Vac/boost leak test around Auckland. I replaced the IACV gasket, the IACV itself and cleaned the MAF. Idle is still very low and rough. I got 140km from half a tank from normal driving so it is pretty bad haha. I do have a venty HKS SSQ BOV though.

Pm me and ill be able to help you out.

[SUBRACY]

Hey! i tried a friend of mines AFM fro a v7 bug and did not fix the issue that actually sounds like it could be my problem as when i start the car it makes a strange rattle like somthing is loose for a second then that sound goes away.. are they pricey parts? and where are they located?

(in regards to the VVT solenoid)

[Rosssub]

http://clubsub.org.nz/forum/showthread.php?22885-New-AVCS-Issue-(V7-on)-oil-feed

[SUBRACY]

 subirex said:

sorry to hijack a bit old thread but have you checked your vvt solenoid? the filters do break and gets stuck to the solenoid and advance the pulley timing sometimes to 50 degrees and gives the same symptoms as you are experiencing.

THIS ^^^

after weeks of checking the simple things like leaks, Plugs and replacing the IACV (although i did pull a P0508) the issue turned out to be the Filter from the bango bolt above the oil control valve dropping the filter directly on top of the Valve. this then caused the filter to be ripped to pieces by the valve and jam it so that it could not function.

I pulled the Bolt off and fished the pieces out of the recess where the bolt lived, I was worried that there may have been more of the filter stuck in the Valve so i pulled that out too and sure enough small fragments were lodged in the Recesses of the Solenoid, Picked those out put everything back together and the car is now smoother than i can remember it ever being.

A massive thanks to Subirex for the tip and Rosssub for the link!.

[Subirex Automotive]

Glad i could be of help.

[KingCole]

 subirex said:

Glad i could be of help.

Thanks Subirex for helping me out with mine too! All fixed.