Stumped- IAC- new computer? - JeepForum.com
 
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post #1 of 13 Old 08-26-2019, 05:56 AM Thread Starter
JT58.bronc66
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Stumped- IAC- new computer?

My 97 has only 21K miles on it, is a time capsule and like brand new. It has been running absolutely fine and suddenly threw a code- P0505 (the typical IAC). Reading the forums so many posts- clean the TB, replace the IAC, look for vacuum leaks, etc.


I have done that and then some. I checked for bad grounds, vacuum leaks, none. The hoses are all in fantastic shape and not brittle at all considering it's a 97. TB is extremely clean. There was trace build up on the original IAC, cleaned it and the port, re-installed it. And I have also installed 2 new IAC's- all did the same thing after installing them. I clear the code, started it up, idled high for a few seconds, idle started to drop and the CEL came on again, then as it warmed up the idle climbed and stays at 1500. I drive it around 10 miles to give the IAC a chance to re-learn, it does not, idles still at 1500. Considering the original one looks fine and installing 2 new ones, I don't think it's the IAC. Cleaned original one with 21K and 2 new bad ones in a row seems unlikely. TB and ports are very clean- look brand new. Throttle butterfly is closing all the way. When you put your finger on the IAC port inside the TB and block it off, the idle drops- so it seems the IAC is not closing the air gap and is not functioning.

So could it be the ECM? Perhaps it's not sending proper signal to the IAC? I don't know how to diagnosis this- is there a way to do it? Anything else I could look for? Are the computers suspect on the 97's?


1997 Jeep Wrangler, 2018 Mustang GT, 2017 Ford Fiesta ST
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post #2 of 13 Old 08-26-2019, 08:51 AM
jtec
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OK you said "it is a time capsule and like brand new" The way I love them !!

The code description is
Trouble Code: P0505 (4.0L L6 VIN S Std) idle Air Control Motor Circuit

key word is CIRCUIT - so changing replacing cleaning might not be the solution...
appears you hav done or are looking to do the last 2 and have NOT addressed 1 and 2.
We can help with the diagrams and some suggestions BUT Can you use a DVOM and read a wiring dia?

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

Sorry if it sounds impatient - am here to help. (hangover)

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 13 Old 08-28-2019, 11:03 AM Thread Starter
JT58.bronc66
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Well I had it diagnosed at a great shop in town. The wiring and harnesses and connections are all good. The ECM is bad. And they are hard to get and probe to problems- especially on the early TJ's I'm told. The ECM's were discontinued in 2016 according to the shop and there is only one source that provides them with any kind or warranty and they cost 1K. Yikes.


Is there a way to get it running without using the ECM?


I'd hate to have to buy a new ECM every year if it goes bad.


I thought that parts were pretty much readily available for these early TJ's- I guess everything but the ECM's.


Will an older straight six bolt in that does not require a computer? Trying to look at all options before I invest 1K, then possibly sell it.

1997 Jeep Wrangler, 2018 Mustang GT, 2017 Ford Fiesta ST

Last edited by JT58.bronc66; 08-28-2019 at 11:20 AM.
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post #4 of 13 Old 08-28-2019, 04:27 PM
Rubi4MyMrs
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Any chance you have (factory) A/C?

If yes, try turning the A/C on & see if the idle speed changes. If yes, normally the PCM increases the speed slightly to compensate for the added load of the compressor & that will tell you if the PCM has any control of the IAC. That will not be conclusive but might indicate something other than the PCM is the problem.

I’m not surprised the PCMs are discontinued. They are also discontinued for most, if not all TJ years including the ’05 & ‘06s. Chrysler is not interested in supplying parts for “older’ models. I can still get parts (when rarely needed) from a local Toyota dealer for my 26 year old 4Runner but not many for the ’05 TJ at Jeep dealers.

I would think you should be able to find “remanufactured” PCMs for less than a grand with a Google search but most internet suppliers have questionable reputations so proceed with caution if the PCM is, in fact, bad.

Here is a bit more info on a guy with the same P0505 code & what he found & some of the things tried while attempting to diagnose it.


https://www.wranglerforum.com/f210/c...l#post34443259
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post #5 of 13 Old 08-28-2019, 04:57 PM
drewtj05
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Flagship 1 PCMs are a pretty good company to deal with. I recently ordered a PCM from them for an 06 TJ that was have the dreaded 1 to 2nd shift issue and the new PCM works perfectly. Cost was around $550

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post #6 of 13 Old 08-29-2019, 04:57 AM Thread Starter
JT58.bronc66
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The shop checked all the wiring, connections, etc. All was good. When they just touched or moved one of the ECM connectors the idle dropped, all kinds of codes displayed, then the idle went high again. He's getting the ECM from the dealer, don't know the actual source but it has 1 year replacement warranty- that he knows he will be able to do an exchange. He has dealt with other sources that won't honor or provide warranty on any electrical parts.


Given that Chrysler is not making part for TJ's any more I think it's time for me to consider getting a brand new JL. I hope I can sell this TJ given that it's hard to get parts for. It's such a shame that Chrysler won't provide parts for such a good legendary machine.

1997 Jeep Wrangler, 2018 Mustang GT, 2017 Ford Fiesta ST
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post #7 of 13 Old 08-29-2019, 06:35 AM
bobjp
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No good reason to buy a new computer. Used computers are readily available considering how badly TJ's rot in the north. Ebay. Craigstlist. You could probably offer someone parting one out on Craigslist $50-$100 shipped. Or contact a TJ / Wrangler parts yard like this place:

http://www.cfoffroad.com/

There are plenty of options and no reason to pay very much. No good reason to go to a dealership for a computer.

You are not limited to a 97 computer. I don't know the exact year ranges that will work, but I'm sure you can do some digging. I have a 94 computer that I was given for free. I've used it while diagnosing issues just to "check the box". It's handy to have around.


I have a feeling you are going to be disappointed after they install that $1000 computer. But who knows.

97 TJ sport.
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post #8 of 13 Old 08-29-2019, 07:21 AM
mukluk
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Quote:
Originally Posted by JT58.bronc66 View Post
When they just touched or moved one of the ECM connectors the idle dropped, all kinds of codes displayed, then the idle went high again.
Based on this, I would suspect the connector is the problem, not the PCM.
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post #9 of 13 Old 09-03-2019, 05:59 AM Thread Starter
JT58.bronc66
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OK, to close this out- it was the PCM. New computer installed and the TJ runs great. So great it's like it got a tune up and a tune. It slightly stumbled before on acceleration- thought maybe it needed new plugs, cap. Now it runs better than ever with more power, no hesitation and ultra smooth and steady idle. There are even warning lights coming on at start up that I have never even seen before. They go out right after start up and no error codes present at all. It's nice to have the TJ running great again.

1997 Jeep Wrangler, 2018 Mustang GT, 2017 Ford Fiesta ST
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post #10 of 13 Old 09-04-2019, 09:50 PM
Jimwfl
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Awesome news! Can you post some pictures of your jeep? I've had my 97 for 20yrs and she still looks mint.
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post #11 of 13 Old 09-08-2019, 04:29 AM
Alexandru
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Quote:
Originally Posted by JT58.bronc66 View Post
OK, to close this out- it was the PCM. New computer installed and the TJ runs great. So great it's like it got a tune up and a tune. It slightly stumbled before on acceleration- thought maybe it needed new plugs, cap. Now it runs better than ever with more power, no hesitation and ultra smooth and steady idle. There are even warning lights coming on at start up that I have never even seen before. They go out right after start up and no error codes present at all. It's nice to have the TJ running great again.
Good afternoon, congrats on making it run again, it appears that I have the same issue with mine. Could you please advise on where can I get a new pcm and as well with the original serial number which appear on the pcm? I am not sure if the one I currently have installed is the original one. I have 2.5L EPE engine.
Thank you
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post #12 of 13 Old 09-09-2019, 10:54 AM Thread Starter
JT58.bronc66
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Quote:
Originally Posted by Alexandru View Post
Good afternoon, congrats on making it run again, it appears that I have the same issue with mine. Could you please advise on where can I get a new pcm and as well with the original serial number which appear on the pcm? I am not sure if the one I currently have installed is the original one. I have 2.5L EPE engine.
Thank you
The PCM's for the TJ's have been discontinued. There are a few places on the internet that rebuild them and resell them. The shop that did the work for me advised against this as often the rebuilt units do not work properly and have to be returned and they sometimes do not take them back that easily. They obtained it from the Chrysler dealer- who obtained it from apparently the only source that manufactures them today. They really do guarantee it and they charge a hefty price- pretty much whatever they want. I paid 950 for mine. You may want to look on the internet or as one person suggested obtain one from a wrecking yard up north where the TJ's rust out fast but the weather is not humid. I have a feeling humidity and moisture killed mine- hot, humid and rainy Florida weather for 7-8 months of the year.

1997 Jeep Wrangler, 2018 Mustang GT, 2017 Ford Fiesta ST
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post #13 of 13 Old 09-24-2019, 11:29 AM
Mostpulp
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I have a 97 grand Cherokee 4.0 & had a similar problem, turned out to be the computer. While your car is running, jiggle the three plugs that go into your computer. If it acts like your car wants to shut off (stalls) it your computer. With mine it was the 3rd plug on the right.
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