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Old 09-07-2016, 07:28 PM
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New member, quick question

Hey guys names Dan I'm from CT, long time jeep owner in the past but just picked up a 99 wj 4.7 in great shape for a steal and figured I'd use it as a winter car.

Long story short it's got the dreaded P0505 idle circuit code and I need it to pass emissions where I live.

I'm a mechanic by trade but mainly work on Italian and German sports cars so I figured I'd throw this one out there for the jeep experts!

So when I pulled the code I cleaned the throttle body and all ports until you could eat off them and replaced the idle control valve. Code returns immediately as well as an erratic idle. Figured maybe bad sensor? Got another from jeep and absolutely no difference.

I noticed it would set a light without even starting the jeep and as the manual states if any of the 4 iac wires short to ground or positive when the ignition is first energized it will set the code within 100ms.

Got the meter out ohm tested the wires from the idle control valve to pcm and found no issues, just because I was pulling my hair out at this point I made a whole new harness from pcm to the idle valve, no difference. All signs point to a bad pcm but runs fine otherwise?


Nervous to buy a pcm and have it make no difference. I've done research on this and have seen mixed reviews. Before I pull the trigger on a new compuTer and advice is appreciated! Thanks

Dan

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  #2  
Old 09-07-2016, 09:46 PM
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Re: New member, quick question

Welcome to the garage.
You have in fact already done all the trouble shooting. In stead of replacing the IAC, you could have disconnected its connector and try again. That the fault continues, shows that it was not the IAC itself and would have saved you some money. You did meassure all four wires for continuity and short to ground or 12V? If so, then there is not more left over then the PCM itself. You could try and remove the IAC wiring pins from the PCM connector and see if the fault continues or not, but you take the change of damaging the connector and creating more problems for the future.
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Old 09-07-2016, 10:28 PM
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Re: New member, quick question

Hi thanks for the response, I did check them and eliminated that as even being a possibility by running my own wires from the pcm to the idle control valve
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Old 09-08-2016, 05:49 PM
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Re: New member, quick question

I was fed up and took the ecu out, hit it with a sledge twice, then threw it off my toolbox and put it back in the jeep.

RUNS MINT!! Idle is perfect
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Old 09-10-2016, 09:00 AM
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Re: New member, quick question

Hi Dannyboost. I have 2 jeeps and a Fiat X19 so I, too, have a sledge in my toolbox. From what I've read, the internal ground in the ecu's on Jeeps can have some ground wires corrode internally and some have claimed to remove the covers and re-solder those to fix problems. Perhaps your sledge and toss method did that
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Old 09-10-2016, 09:26 AM
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Re: New member, quick question

Quote:
Originally Posted by pbruecken View Post
Hi Dannyboost. I have 2 jeeps and a Fiat X19 so I, too, have a sledge in my toolbox. From what I've read, the internal ground in the ecu's on Jeeps can have some ground wires corrode internally and some have claimed to remove the covers and re-solder those to fix problems. Perhaps your sledge and toss method did that
What year x19? I built one at my shop with a Honda k20 engine with the Bayless kit, thing was a beast! Also did another 2liter build a few years ago, always liked those cars
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Old 09-10-2016, 10:47 AM
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Re: New member, quick question

Welcome to the Garage. Get a bigger hammer has worked successfully for many years. I liked the extra added insurance of throwing the toolbox, excellent tip! See you around the forum.
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Old 09-13-2016, 04:04 AM
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Re: New member, quick question

Hey Dan
Glad to hear the percussive adjustment saved the day! In case the problem returns, try this to reset the 'adaptive memory' in the PCM. Sure seems like it could not be the new IAC or the new wiring harness you built, hence looking at you (PCM). They are pretty tough it seems and there was no CEL when you bought it so some thing just 'surfaced'.




This very simple procedure will Erase the“Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to bedeveloped.

After performing this procedure the PCM will re-learn and store into AdaptiveMemory your engines performance characteristics.

Please perform these steps exactly as they are written, in the order they arewritten. This will cause the adaptive memory in the PCM to be erased and causethe PCM to go into Fast Learn Mode adaptive mode.

Disconnect the POSITIV batt Terminal and touch it to ground ( NOT the battnegative terminal ) for 30 seconds. The engine block or the A/C compressor pumpwill work as a ground. (This is to discharge the PC capacitors, which maintainthe Adaptive Memory.

1) Turn Ignition Switch to the “On” position but DO NOT start the engine
2) Turn Headlight “On”
3) Turn Headlights “Off”
4) Turn Ignition Key “Off”


The PCM Adaptive memory has now been flashed, or erased from the PCM.

When you start the engine it will be running off a set of pre-programmed tablesthat come with the PCM from the factory.

When you get the engine up to operating temperature the PCM will start tocollect data for the “Adaptive Memory”.

The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.


Bonne chance!
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  #9  
Old 09-13-2016, 07:34 AM
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Re: New member, quick question

Hi Dannyboost. I have a '76 X19 that is pretty much stock. It's my summer car with my WJ for winter, just like you. I found the last thread about re-flashing the PCM very useful to know...
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