P0505 - Idle Control System and a High Idle - Call for help.

Hi guys...I’m running out of ideas on this, need some input please?

2002 3.4L V6 5spd 4WD.

Trying to get my POS smogged, I have had multiple system codes that I have worked though...

I was getting Throttle Position Sensor and Idle Control System errors all while my idle was running high (1150-1350)

I searched for the issues, and based on what what I read it sounded like a simple fix so I pulled the throttle body and went to work cleaning …

I removed and cleaned the throttle body thoroughly and removed and cleaned the IAC which was pretty gunked up and not moving at all. I cleaned and tested the old IAC. Testing indicated it was working properly. Reassembled... No difference.

Then, I replaced the IAC (and gasket) and the Throttle Position Sensor. TPS error gone, but no luck on the P0505

Next I replaced the IAC a second time, no change.

I read that the computer somehow needs to [re-learn] about the new components to I cut the battery for an hour or so...nothing.

I read that the linkage can be sloppy and a thin washer can be added to take out the slop...I don’t have any slop so that didn’t help.

Currently have a high idle and throwing [P0505 - Idle Control System] and the idle is hovering around 1150-1350.

I’ve had the throttle body off at least 6 times, tried 2 different IAC units after I tested the old one...not sure what to do next...I checked vacuum lines, they all seem connected...thinking it needs to go to a real mechanic...sigh.

Any input or ideas will be greatly appreciated.

 

as a test, disconnect and plug the vacuum line to the brake booster and see if the idle drops. Then check/replace the PCV valve. These dont take long or cost too much money.

 

Thanks for your input sir, I will give that a try tomorrow. Didn't get a chance to work on it at all today.

 

You need to remember it is the Complete circuit not just the IAC !!

The wiring and the ECM/ECU what ever you use .


Seems like the IAC has not worked for some time.

Was the coolant temp sensor sending a faulty signal keeping the IAC open ??

Air being sucked in up stream of the MAF sensor ?

Having worked through this The ECM did not need a learning process .

In my case it was the ECM on my 3.4 swap got wet

 

The water temp sensor was suggested yesterday by a mechanic...more things to try, thanks!

 

Ive had a similar issue i've been battling on mine (I have the 2.7). I essentially went through the same steps you did, replacing the IAC multiple times (I was never getting a TPS code though). I since have done the cylinder head (Unrelated issue) and during that replaced the Engine Coolant Temp Sensor. Now my truck behaves really weird and is not getting any codes. When I start the RPM are very low and it lopes, so you have to open the throttle a little bit to get it to idle around 1,100 to warm up. Once warm the idle stays around 1,000-1,100. It is behaving opposite cold starting at low RPM and transitioning to high RPM once warm.

Ive checked all the vacuum lines and it isn't the MAF. So i'm thinking mine is either a bad ECT (Cant remember if the one I got was OEM or not) or an ECM that has gone bad.

I will have to disconnect the brake booster and see if that does anything at idle, haven't done that yet. Also haven't replaced the PCV, but shouldn't it draw a code if the PCV is malfunctioning?

The only other thing I have, which I cant figure out is I have what sounds like a vacuum hiss, but it is coming from the back side of the block around the area where the EGR pipe comes off of the exhaust (Drivers right side of the block). I don't have any vacuum lines around there, so i'm really not sure what that is. Anybody have any input here?

 

OK, mine is fixed and running well now, waiting for systems to be reset. Turned out to be the throttle body, after putting an ebay one on and finding it to be not exactly the right one, then got one from a bone yard that came in with a broken TPS...good thing I already had one of those on hand.

BIG THANKS to all who offered suggestions and support!

On to the next issue...