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So this is odd...

Discussion in 'Minivans · Pacifica' started by CudaPete, Jul 1, 2017.

  1. CudaPete

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    Getting ready to weld some patch panels on the 02 GC today. Had just disconnected the negative terminal on the battery when it looked like some storm clouds were rolling in. Electricity and water don't mix so I decide to table the welding and move on to another project on the "honey do" list. Reconnected the ground and went to start the van. Cranks fine, starts, and then promply dies. Try it again, same result. Try holding the gas down a little (normally don't have to do this) and it starts, runs, and idles roughly in park at 500 rpm. Shift to drive and stays at 500 rpm. Shut off the van and remove the batter cable, clean it and battery post. Reconnect, start van same result, 500 rpm in park. OK, maybe throttle body is dirty. Remove intake hose and clean throttle body. Start van, 500 rpm. No CEL and engine revs up fine. The van drives and does not stall, just low idle in both park and drive, 500 rpm. So, I decide to go for a ride. Slowly, it starts to come back to life. It now idles in park at 800 rpm and in drive at 600 rpm. Pretty much where it normallly is. Not so rough anymore either. It ran fine just before I initially removed the negative battery cable. No codes ecept 1684 which is expected. Any thoughts?
     
  2. dana44

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    2002 is, and I assume this is for all Mopars starting then, have learning computers that can detect a driving style basically. Now, when a battery is disconnected, after a short period, between 15 and 30 minutes, the computer will reset to factory default settings. The reason I mention this is because the computer learns, calculates, and adjusts parameters to sensors, exhaust output, throttle positions and shifting speeds, and taking all these factory settings and starting over makes the computer recalculate all the driving parameters. Not sure why the idle itself would be as low as you noted, unless the intake air control (for idle) or the throttle position sensor is worn, the computer should correct for that through rpm itself. It is a case of, once she warmed up and was driven, things went back to normal, as it should be, and kind of leave it at that, the computer did what it was supposed to do in the end.
     
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  3. Crawdaddy

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    The PCM adaptives had corrected for carbon build up in the throttle body and IAC. So when reset the idle was too low until the PCM could readapt.
     
  4. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Other possibility is that it didn't have a good connection when you reconnected. To test, measure voltage between the negative post and the negative clamp with headlights on. Then measure between negative clamp and block with headlights on. Voltage reading should be 0.1 volts or less. If more than 0.3 volts, there is a bad connection.
     
  5. CudaPete

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    Ran fine this morning so it must have been the relearn as suggested. Thanks.
     
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  6. valiant67

    valiant67 Rich Corinthian Leather
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    Of all the Chrysler products I've owned, there were two that consistently "forgot" how to idle any time they lost battery power. I had to help them idle a minute or so after battery replacement then they were fine.
     
  7. CudaPete

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    It seemed "confused" is the bet way I can describe it. I did clean up the battery posts/cables and the throttle body. Just needed about 10 minutes of driving before it figuered things out. Ran fine all day today.
     
  8. vipergg

    vipergg Well-Known Member

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    Once you pull power the pcm resets and loses all the operating parameters it had learned and goes back to factory defaults, it will then slowly relearn the as you drive.
     
  9. dana44

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    Yes. This is why when a check engine light finally pops and a sensor is changed, it will run like garbage for about the first half hour sometimes, because the computer had compensated for the problem as long as possible, then had to relearn. Same thing happens after you change the part and if you disconnect the battery for the 15-30 minutes, the calculating by the computer takes less time because it has erased all those recalculations and is now adjusting from factory settings.
     
  10. CudaPete

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    I'm planning on trying to do the welding on it again this weekend. Any thoughts on how to prevent it from getting stupid when I disconnect the battery?
     
  11. dana44

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    It might not get as crazy this time around, given it might not have to adjust as radically next time around. One can hope. Otherwise I have no means of being able to keep things connected and still disconnected to make corrections after the fact. At least you know it has the ability to correct itself after the battery is disconnected.
     
  12. CudaPete

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    It did not get allout stupid this time, just a little dopey for a few minutes
     
  13. CudaPete

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    So, I may have spoken a liitle too soon. Running rough at idlel today, 500 rpm, and CEL pops on. P0172 Bank 1 running rich. Could htis be caused by the btterey disconnect or just a coincidence? Never had this one before.
     
  14. CudaPete

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    Also seing a P0456, small EVAP leak. Wonder if they are related.
     
  15. CudaPete

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    Just got back from a 20 minute ride. CEL went out on its own. P0172 is still stored. P0456 is gone. Idling at 650 rpm in drive now. Maybe a stuck injector that freed itself up?
     
  16. CudaPete

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    Runs better with the AC on????
     
  17. CudaPete

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    I still have one more side to do.
     

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  18. CudaPete

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    Fixed the P0456. One of the hoses had a crack in it. But now P0172 just came back. I'm thinking upstream O2 sensor since this car does not have a MAF sensor. Any ideas?
     
  19. CudaPete

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    Code 172 comes and goes along with a rough idle in gear. Not an intake leak and not the converter.
     
  20. ImperialCrown

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