00' XJ P0505 off and on but runs fine....

First I searched and didnt come up with any posts that had the same symptoms as mine.

I have been getting the P0505, idle control system malfunction, code off and on for the last two weeks. First two I cleared the code stayed away for a few days then returned. It now clears itself at random. Weird thing is that it runs fine, idles with ease. The tach does have a slight blip or drop or rise in rpms on rare occasion at idle, motor doesnt sound to be stumbling.

My thoughts are that it is the IAC on its way out or maybe just a dirty/loose connection. Question is could it be anything else? Thanks

Its telling you that there is a "short" or "open" in one of the IAC circuits. Could be internal to the IAC or the harness. Start with cleaning the contacts and give them a little dielectric grease.

I agree. A good spray of electrical contact cleaner in the connector, a dab of dielectric grease, reconnect and see if that resolves it.

If it doesn't, I'd replace the idle air control.

Thanks thats what I was figuring, but my lousy hanes manual doesnt provide much info and wanted to know if anything else could cause it. Time these days are limited and with this being my DD cant afford to have it not start one morning.

Well, the beauty of OBD I and OBD II is there ability to store codes and give a technician a STARTING POINT in repairs. The downside is that too many people believe the codes indicate a specific problem or component fault. All the codes are telling you is that the PCM is not getting data/results that it expects from a particular data stream under certain conditions, or that is what the PCM thinks is going on.

So, your problem could be a faulty IAC, a fault in the harness between the IAC and the PCM, the PCM itself, or it could be a combination of things. Test and check as a process of elimination.

Dealerships have extra tools the average shop and owner won't, like the tester for the IAC.

Good luck, post up what you find.

well I hosed it down with electrical contact cleaner and greased her up. Code is still popped but dont know if it needs cleared. Thinking with how it reacted before that it will clear itself when it sees what it wants. I suppose I could have cleaned the contact with something abrasive but dont have anything that small. Guess its time to dig deeper, damn, was hoping for a quick fix.

replaced IAC now a new problem has risen....

see link for old post
http://www.naxja.org/forum/showthread.php?t=1043679
So I just replaced the IAC as it was beginning to have trouble idling now. Idle would drop down around 400. Now with the new IAC it idles fine but the throttle is all messed up. If I tap the throttle it, the engine, keeps accelerating on its own. Say another 600 rpm, then slowly drops back to idle. Kind of like your foot is still on it and you are slowly lifting off the pedal. This obviously make for a dangerous ride as I have to keep a heavy foot on the brake.

I cleaned the throttle body and IAC port still doesnt help. Im wondering if I got a bad IAC or does the computer need reset? Also I checked the throttle plate and it is returning to normal. Seems like the IAC is slow to respond and causing this. Any other ideas aside from trying yet another IAC? Thanks

Re: replaced IAC now a new problem has risen....

Ok, you need to test the harness between the IAC and the PCM.

I don't have access to the 00 PCM pin out today, hopefully someone else will post up with the info.

Re: replaced IAC now a new problem has risen....

Okay Ill look in my Hanes not sure it is that detailed in the wiring.

Re: replaced IAC now a new problem has risen....

Ah, the dark side of the Force!

Haynes, that is.

Too generic, attempts to cover too many years, and too many outright ERRORS to be of any real use.

Good luck.

Re: replaced IAC now a new problem has risen....

Yes you are right it out right sucks. I was able to borrow a buddies FSM today and holy chit those things are awesome. Thats what a manual should be. Wish I would have had one along time ago.

As far as the problem goes it is fixed now. There were no bad wires or connections, dirty or corroded. I pulled and cleaned all associated harness and even fuses/relays for the hell of it. I also checked the brake light switch, so I guess you could say I reseated it. I left the computer unplugged for 30 min to reset it. Plugged it all back in and it works like a charm now.

My guess is that the IAC was bad and the computer needed to be reset kinda like with new O2 sensors. I would imagine you could use that as rule of thumb that for any major engine sensor it is a good idea to reset the computer. I havent found that printed anywhere, but as with most anything computer controlled, when in doubt reboot.

Thanks for all the help, I will post if the problem comes back.

A FYI for those troubleshooting IAC or other problems.....

I recently had problems with my IAC, I replaced it and had new problems arise. Ended up the computer needed rebooting, unplug for 30 min. I would imagine you could use this a rule of thumb for all major senors or computer related things. When in doubt reboot.

Another by the way be sure when unplugging or messing with the PCM to first disconnect the battery. FSM warns of this as voltage spikes can be very damaging to the PCM.

For background info on the above see link below.
http://www.naxja.org/forum/showthread.php?t=1043771

Re: replaced IAC now a new problem has risen....

Check to make sure the throttle cable isn't causing the problem. Unsanp it then blip the throttle by hand and see if it reacts correctly.

Re: replaced IAC now a new problem has risen....

Well if it acts up again I will recheck that. I did check that the first time around as stated above, but with the cable attached. It appeared to function properly. Ill try next time with the cable unhooked.

Re: replaced IAC now a new problem has risen....

Unplug the battery and give it 10 minutes. 70% of the IAC's i've installed on late model 4.0's need a computer reset to make them happy. Heck, even on mine it's hit and miss just taking it off and cleaning it (sometime's it will fire right back up normal, others it fires up with a high idle).

I've also had luck with them eventually adjusting after driving it around town for a little bit.