P0506 Idle Air Ctrl Sys and Failed smog test

[Homeoboxter]

Dear All,

I hooked up my code reader which revealed the following code: P0506, idle air control system failure. The engine has a stable idle when cold, ~800, when it warms up it goes a bit over 1000 and fluctuates between ~1100-1200. I`ll look into this tomorrow but I thought I ask the Community first if there`s anything obvious to look at with these symptoms. Intake plenums and throttle housing are cleaned, the whole engine has just been freshly put together.

Not sure if related, but the car failed the smog test yesterday. Emission is fine, I was told the reader could not reveal the fault code history because the battery was disconnected for too long, for 13 years actually. So I was told to put a couple hundred miles into the car and go back and it would pass...

Thanks for any insight.

[JFP in PA]

P0506 code is for idle speed too low, common issues is the IAC valve sticking or a blocked air filter element.

[Homeoboxter]

Originally Posted by JFP in PA

P0506 code is for idle speed too low, common issues is the IAC valve sticking or a blocked air filter element.

Thanks, JFP, for the quick response. I`ll check the valve tomorrow. I also noticed that when I operate the throttle and the engine is revving the intake plenums get a bit "inflated" like some "lungs". Is that normal? I would expect the opposite..

[JFP in PA]

That does not sound correct.

[Homeoboxter]

Update: I fixed the code issue, it was indeed the IAC valve, thanks for the suggestion. It wasn`t really dirty, but I think it was stuck. I disassembled and cleaned it out and now idling is stable and the code s gone.



I made a video of the intakes expanding, uploaded it here:
https://www.youtube.com/watch?v=8C2ZBcO4WZY&feature=youtu.be

Perhaps the new rings need to wear in and not seating perfectly yet..

[911monty]

My 98 "breathes" exactly as yours does. At first I was concerned until I realized what is happening. With throttle closed and max vacuum in intake plenums, everything is drawn together. When the throttle is opened intake manifold vacuum drops and the intake manifolds relax appearing to expand. I may be wrong.

[Homeoboxter]

Originally Posted by 911monty

My 98 "breathes" exactly as yours does. At first I was concerned until I realized what is happening. With throttle closed and max vacuum in intake plenums, everything is drawn together. When the throttle is opened intake manifold vacuum drops and the intake manifolds relax appearing to expand. I may be wrong.

Oh, yes, that totally makes sense. These plenums are pretty well made that they withstand so many expansions in so many years.

[911monty]

Originally Posted by Homeoboxter

Oh, yes, that totally makes sense. These plenums are pretty well made that they withstand so many expansions in so many years.

A bit inverse to the normal thought process. Any insight to that IACV? I'm thinking I'll put that on my to do list!

[Homeoboxter]

Originally Posted by 911monty

A bit inverse to the normal thought process. Any insight to that IACV? I'm thinking I'll put that on my to do list!

It`s a super simple 30 mins job. I didn`t remove the throttle body but I knew it was clean. Just pulled the AOS-to-throttle body hose off, removed the two torx screws and the connector and pulled the valve off. Be sure you don`t damage the paper gasket if you don`t have a new one. For cleaning it`s not necessary to disassemble the valve unit but it`s easier to inspect and clean the parts if you do so. There`s a copper/brass pin that has to be pulled out, I used a wood screw and a plier to grab it. Then you just need to twist the two halves against each other to unlock the bayonet lock and they come apart. There was a little dirt and dust in the valve unit and also around the magnet that made it stuck. I dropped both into a jar with gasoline, shaked for a minute then dried them with compressed air and reassembled.