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P0505, IAC, high idle woes, and bee smokers.

 
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  • 1 Post By rob342
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  #1 (permalink)  
Old 21 Nov 2015, 04:44 pm
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Default P0505, IAC, high idle woes, and bee smokers.

Hey guys,

I've got a 2002 PT, normally aspirated base-as-heck model with a 5 speed. Last week it threw a P0505 code with no noticeable symptoms other than a mildly elevated idle (about 1000ish instead of the usual 750-900). I checked the IAC motor wiring for voltage, and the circuit itself seemed fine, and as a result I replaced the IAC motor (wiring is good, so it seemed logical to be the motor itself).

Once I replaced it the engine started and went to about 3000 rpm, then settled down and surged around 1500 a little bit. After about 5 minutes the idle dropped to around 750 and held. Drove around about 30 minutes, check engine light was gone.

Fast forward 2 days and the light comes back on about 30-40 minutes into the drive. Coming to a light and depressing the clutch pedal I got to about a 3000 rpm "idle". It wouldn't come down, so I pulled off. Started it up to head homeward and on the way home it started behaving. Another 30-40 minute drive and the light goes off again. Today was a repeat of the above, but now the idle isn't returning at all, and/or it's surging around 1500 rpm.

I probably looked crazy when I pulled out my bee smoker (I'm a beekeeper) and started smoking the engine bay looking for a vacuum leak, but I couldn't find anything...

Any suggestions or similar experiences?
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Old 21 Nov 2015, 05:51 pm
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Location: Thousand Oaks, CA
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Default Re: P0505, IAC, high idle woes, and bee smokers.

P0505 - Idle Air Control Motor Circuit issue

Possible Causes:

Stepper motor Coil No. 1, 2, 3 or 4 circuit open or shorted to ground
Stepper motor coil circuit(s) shorted to system power (B+)
Stepper motor is damaged or has failed
PCM has failed

I would suggest double checking the wires from the Stepper motor to the PCM. Make sure the wires are not shorting each other.
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Last edited by ptcruisersteve; 21 Nov 2015 at 06:11 pm.
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Old 22 Nov 2015, 10:41 am
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Default Re: P0505, IAC, high idle woes, and bee smokers.

first thing is to verify the TB actually closes all the way and check the wires as he suggests.

then

remove the IAC, verify it is closed, reinstall it, and leave the electrical connector unplugged. if it seems better, leave it unhooked and see how the car behaves.

personally, i always liked my PT better with the IAC disconnected, as it made the RPM drop quicker and decelerated faster when i downshifted. particularly in the summer when the AC was on.
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Old 18 Jan 2016, 05:44 pm
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Default Re: P0505, IAC, high idle woes, and bee smokers.

I just wanted to update this with my findings so nobody is left hanging. The end result was a bad PCM. The wiring to the IAC checked out fine from the PCM end to the IAC itself via resistance and wiggle testing. After replacing the PCM everything worked, no codes, and a clean idle. Unfortunately a few days after replacing it I now have another issue for another thread...
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Old 19 Jan 2016, 12:37 am
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Default Re: P0505, IAC, high idle woes, and bee smokers.

Where did you get your replacement PCM ?
It takes about 45 miles of driving for the PCM to become ready for all monitored systems.
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Last edited by JoeX; 19 Jan 2016 at 04:42 pm.
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Old 19 Jan 2016, 10:48 am
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Default Re: P0505, IAC, high idle woes, and bee smokers.

Quote:
Originally Posted by rob342 View Post
first thing is to verify the TB actually closes all the way and check the wires as he suggests.

then

remove the IAC, verify it is closed, reinstall it, and leave the electrical connector unplugged. if it seems better, leave it unhooked and see how the car behaves.

personally, i always liked my PT better with the IAC disconnected, as it made the RPM drop quicker and decelerated faster when i downshifted. particularly in the summer when the AC was on.
The engine light would probably stay on if the IAC was disconnected.
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Old 19 Jan 2016, 06:43 pm
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Default Re: P0505, IAC, high idle woes, and bee smokers.

Quote:
Originally Posted by JoeX View Post
Where did you get your replacement PCM ?
It takes about 45 miles of driving for the PCM to become ready for all monitored systems.
I installed a reman unit from Ebay, and after installing it drove approximately 75 miles. My fiancee then drove the car about 500 miles (250 each way) and once she pulled off the highway (home bound, thankfully) the car started missing and shuddering. The first 325 miles were fine.

So, since I hadn't shipped back my PCM yet I stuck it back in the car and the engine was behaving the same way as with the new PCM (except of course the IAC circuit is bad). It's running like it's misfiring on a cylinder, but isn't throwing any codes. I've got the replacement PCM back in, and I'm doing some investigation (pulled plugs (new) to inspect for fouling etc.)...
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