So a CE light came on on my car last month with a P0508 Idle Control System Circuit Low. What the car is doing is that it has a erratic idle. The idle goes from 1000 to 1200 RPM. First thing i checked was my IAC valve removed it cleaned installed new gasket after all that car started to idle at normal rpm. Following day it started idling bad so i checked all vacuum hoses for brittle or cracked hoses all in perfect condition and sprayed them with brake cleaner for a change of idel. Followed the Diag Procedures for that code and found that it had low resistance on the ECM connecter pin for the IAC valve. It said to repair connection from connector and ECM. Checked the ECM pins and connector for any damage all looked ok. Bought a used ECM to see if my old ECM went bad but i guess it did not. I even changed the IAC but all it did is idle the car at 1500 rpm all the time


Car is a 02 WRX Automatic
Engine Mods: 660cc injectors, Walbro fuel pump, VF34 turbo, Perrin turbo inlet. SPT cold air intake, STI TMIC with samco hoses, current ECM is stock not tuned using it for testing only the Old ECM is on stage 2

If anyone has some ideas with fixing this I would highly appreciate the help

 

you got the TB nice and clean too?

 

Hmm, time to take it to a shop.

 

Yea cleaned it well while with TB cleaner engine only has like 14k on it. Its a complete 05 ej20 swap

 

Well im a subaru tech and thats how i got all the diag steps for that code. Not even the experienced techs knw why its doing that

 

Hmm. I had a similar issue a LONG time ago. Samething with erratic idling, but after changing out the IACV it was fine. At this point check connections, bad grounds maybe?

 

+1
im surpirsed it indeed is not the IACV or TB as i too has this issue with erratic idling at a stop. i replcaed IACV with gasket and cleaned TB thoroughly. never had the issue again.

also +1 with the ground or wiring, seeing as it is a swap and a connection could be coming loose. did you check voltage readings on the actual IACV? (see how many Volts drop when you rev engine. same for TB. maybe your TPS is not adjusted correctly?)

 

Im going to have to connect the subaru computer and see if the TPS is working properly. I never thought of checking the harness if it was coming lose ima check that to. I also notice the alot of wrx's have the same problems but they never posted on how they repaired it. But yea ill double all your ideas

 

+1. its sometimes the small tiny things that get overlooked. Like me. almost tearing deep into my engine to find out why she didnt start. my lady's father, who is a big time mechanic, called and said to check all my connections. turned out my primary to coil pack was loose. You know, the one staring you right in the face??? LOL. GL!

 

Do you have an accessport? You can log the TPS and datalog to see what voltage your getting.

 

Haha oh ive had times just like that lol. But yea need to start looking in deeper into that problem

 

I do but its the Version 1 and idk how to do that or if it has that option?

 

Check your throttle and cruise control cables....after my swap, I had them too tight.....also, when you cleaned your IACV, did you remove the motor/solenoid? I cleaned mine one time but didnt remove the solenoid and make sure the flapper spun freely so it still didnt fix the issue. I ran across a thread on nasioc explaining cleaning under the flapper and sure enough, worked like a charm and no CEL's or idle issues. Also, make sure to reset your ECU after you clean the IAVC....sure you know that already though....good luck!

 

Cables are good... I took the IACV that is from my old engine removed those two 5 point torque screws notices that the valve or flap as you mentioned does not even move like it seized up...when i hooked this IACV last time the only thing it did was made the engine idle at 1500 rpm so now if im correct the reason it idle high was because the valve dont even move

 

I've replaced my iacv and that corrected the idle issues check out www.rockauto.com I got my last one from there and haven't had any issues since then, I've also replaced the bolts and got a new gasket. Hope this helps.