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hedine
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May 18, 2010, 7:19 PM
Post #1 of 6
(1712 views)
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99 ram IACV problems
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1999 dodge ram 1/2 ton, 4X4, auto, 5.9/360. 139k.
My idle air control valve does not close. My engine has been running high for quite some time. At idle it was very high, very rich, the air intake is extremely loud. My mileage was reduced to about 4mpg. The CEL came on at the same time as the symptoms. After replacing multiple sensors and small parts, including fixing an open wire between the IACV and the PCM, and replacing the IACV twice, I pulled off the intake down to the throttle body. While on and idling, the IACV is wide wide open. If I partially closed the whole with my finger, the engine speed came down. So far, no one at any auto shop has been able to help me. I have replaced my TPS, coolant temp sensor, MAP sensor, then reinstalled the original and returned the new because there was no change, I have cleaned both O2 sensors, searched high and low for vacuum leaks, and changed IACV. I have also cleaned the throttle body thoroughly, and there is no MAF sensor. I also replaced spark plugs and wires less than a year ago. The associated error code is PO505, idle air control system or something along those lines. A local mechanic used his computer to try and tune the RPMs down to normal but the engine would not slow, but it would speed up if he commanded it to. When I turn the engine on cold, it idles around 1200. After it warms up, if I pull up to a stop, then engine runs around 800. If I shift into park it is also around 800, which is normal. If I turn my truck off and turn it back on hot, regardless of time elapsed, it runs around 1600. Restricting air flow into the intake slows the engine to normal, but cutting off air completely kills it immediately, so I’m skeptical of a vacuum leak. This has been going on over two months because no one has any answers. About two weeks ago, while accelerating to highway speed from a stop, the engine couldnt get passed about 40-45. When I hit about there, it felt like it was possibly starved of fuel, or possibly (worst case scenario) couldnt complete the shift up to the next gear. That has only happened once though, and I have been on the highway many times since then. Also, there is an occasional backfire.
Also possibly helpful (or not), about two and a half years ago the transfer case exploded, quite litterally. the outer case broke into pieces with no prior indication of any problems.
I found out how to test TPS function and did so. The three wires are ground, 5v reference, variable return. On a multimeter, the ground to reference should be right around 5.0v. At idle and idle poition KOEO, ground to variable should be at 0.9v, which it is. At wide open throttle KOEO the ground to reference should be close to 5.0v, around 4.5. My old one that I replaced only reached about 3.3v so i replaced it, but the new one is no different. Continuity is full between PCM and TPS.
I think that about sums it up, please tell me what I should do next, besides a big bullet.
(This post was edited by hedine on May 18, 2010, 7:23 PM)
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Sidom
Veteran
/ Moderator
May 20, 2010, 8:14 PM
Post #2 of 6
(1692 views)
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Re: 99 ram IACV problems
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This system uses a dual coil stepper motor to control the idle, basically one coils goes up & one down....
Normally when one coil goes out you'll get a P0505 and either it won't idle up or won't idle down.....
You said you've already changed the IAC and that didn't help so now the circuit and PCM needs to be looked at..... I really don't know of a good way to test this without a 2 ch scope & a scanner with bi-directional controls but maybe some else has a good trick they know of & will chime in... Maybe your mechanic can help you out with this, he has the scanner maybe he has a scope as well.
pins 1 & 4 are for coil 1 & pins 2 &3 for coil 2 on the IAC connecter. Do one coil at a time, running with the lights one the patterns should mirror each other then command it up & down and you should see the patterns change accordingly........
Sounds like you either have a bad wire or bad driver in the PCM.......
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hedine
New User
May 20, 2010, 9:55 PM
Post #3 of 6
(1684 views)
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Re: 99 ram IACV problems
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So I don't know how I forgot to mention this before , but there was an open wire somewhere between the IACV and the PCM. I cut the wire at both ends and just spliced in a new one to take care of that problem, but there could have been a short that fried something. I also hooked up my multimeter to it. With the key on, pins 1 and 4 at the plug end of the wire had 11.92v constant. Pins 2 and 3 had 4.15v at idle and 4.16 at wide open. It seems like that would narrow it to a PCM, but I'm not a professional so please let me know.
Also, if that is the case, do I need to follow the wire and find where it's open to make sure it isn't arcing across to another, even though there is no current going through it?
Thanks a ton
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Sidom
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/ Moderator
May 22, 2010, 7:45 PM
Post #4 of 6
(1671 views)
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Re: 99 ram IACV problems
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I am going off memory and will have to check my database for the exact voltages, it's been a while since I had to check one.
It does sound like you have a problem on the #2 coil. Since you had that wiring problem it's very possible you have some wires shorting, pulling down the voltage. To check for a short to ground & the continuity of the wires you could disconnect it from the IAC & PCM, make sure the wires have continuity and then probe the wire & ground and there shouldn't be any continuity, if there is then you have a short.........
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hedine
New User
May 23, 2010, 9:40 PM
Post #5 of 6
(1668 views)
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Re: 99 ram IACV problems
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I had a short before, I found it like you just told me to. I fixed it about a month ago by just cutting the shorted wire at both ends and splicing a new wire in. Then, just to be safe, I did the same to the other three wires. That's why I'm thinking that if the problem seemed to be either wiring or PCM, it would have to be PCM. Now all four wires have full continuity and are outside the main bundle, there's not really anything to impede them. If the problem is a bad PCM, should I follow the old wire that had a short and make sure it's not next to another open wire for something else unidentified? If a short between the IACV and another open wire fried the PCM, it seems like that may happen again if I put a new PCM in and don't fix any shorts, if there are any.
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Sidom
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/ Moderator
May 24, 2010, 10:09 PM
Post #6 of 6
(1661 views)
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Re: 99 ram IACV problems
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I'm just a little concerned about that low voltage on pins 2 & 3. It's very possible you have a short pulling the voltage down but the bad thing is, it's also possible you have bad drivers in the PCM....
I would have to reread the post but you should have 12v on pins 1 or 4 and then on 2 or 3 with the it disconnected & KOEO but not on all of them at the same time.......
The only way to know for sure would be to isolate pins 2 & 3s circuits from the PCM (remove the pins from the connecter)and then measure the voltage. If it's now correct, you have a short somewhere, if it's still low then the PCM is bad.
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