1999 5.9L Rough (bouncing) idle = IAC
Thread Starter
|
Registered User
Joined: Sep 2010
Posts: 13
Likes: 0
1999 5.9L Rough (bouncing) idle = IAC
Hi All.
I have a 1999 5.9L Durango 4x4 SLT. 135k on the engine. It started running rough at idle a few weeks ago and I was finally able to fix it today. I thought I'd share some of the debugging with the forum for future reference.
Symptom: Rough Idle. Low RPMs with the RPMs sometimes bouncing between 400 and 800 RPM. Often the engine would die. With the Drivetrain in Park (or neutral) I could rev the engine to about 2000 RPM to warm it for a while, and then it would (mostly) run fine. Subsequent starts during the day exhibited the same symptoms, although perhaps not for as long of a time (I believe that engine temperature was playing a role in this).
I scanned a number of threads on this forum as well as the internet, and over the last few weeks have checked on these items:
I have a 1999 5.9L Durango 4x4 SLT. 135k on the engine. It started running rough at idle a few weeks ago and I was finally able to fix it today. I thought I'd share some of the debugging with the forum for future reference.
Symptom: Rough Idle. Low RPMs with the RPMs sometimes bouncing between 400 and 800 RPM. Often the engine would die. With the Drivetrain in Park (or neutral) I could rev the engine to about 2000 RPM to warm it for a while, and then it would (mostly) run fine. Subsequent starts during the day exhibited the same symptoms, although perhaps not for as long of a time (I believe that engine temperature was playing a role in this).
I scanned a number of threads on this forum as well as the internet, and over the last few weeks have checked on these items:
- Battery (a bad battery will drag down the alternator after start, putting load on the engine).
- Cleaned the battery posts and terminal connections
- Had the battery (1 yrs old) tested at a service shop
- Double checked battery voltage before, during, after start with a voltmeter (~11.8V during start, rising quickly to 13.5 volts once the alternator is engaged).
- Spark plugs
- Changed the spark plugs to Champion Copper with 0.040 gap. I couldn't tell you when mine had last been changed, so this was something I was going to do anyway.
- The plugs didn't look too bad. Typically light gray/brownish coloration, and few deposits.
- The old plugs had worn, and now had a gap of 0.045 to 0.055 depending on the plug.
- The engine did seem to run better (at speed) after the plug change, but it didn't help with the rough/bouncy idle.
- Idle Air Control Valve
- Replaced the IAC, and this fixed the issue. No more rough/bouncy idle.
- The IAC is located on the back of the throttle body towards the passenger compartment.
- Need to remove the air intake on the top of the throttle body.
- Disconnect the electrical connector on the IAC
- #25 Torx for the (2) screws
- Cost for a new one was ~$40 at Autozone
- After replacement, the truck immediately ran fine. No need to reset the PCM.
- This youtube video shows the IAC location. (http://www.youtube.com/watch?v=oNO8G...eature=related)
Hall Of Fame
Joined: Jun 2005
Posts: 14,228
Likes: 19
From: Riverton, UT
1st. Your using a 2000 Dakota 3.9L but I guess the principle is still the same for the 3.9L, 5.2L, and 5.9L however it is not a Durango.
2nd. The air box stuff and the "whatever this is called that sits over the throttle body" that you take "loose" is called an Air Hat, Air Box, and Intake tubing.
3rd. The PVC Crank Case Breather is 2 seporate and distinct things. You have a PCV valve that goes into the Intake Manifold for vacuum. This is located on the valve cover and each year is different. On the opposite side is the crank case breather line and it attaches to the Air Hat on the back side. This is so filtered air can inlet into the crank case and be drawn out on the other side of the motor to remove the monoxide from blow-by so it does not acidify the oil.
4th. The IAC valve does not say how much air goes into the throttle body. The MAP sensor detects the air volume and the IAC also air to go around the butteryfly on the throttle body as it is closed. During cold start or cold running the IAC opens more to allow more air to go by keeping the stoichiometric air/fuel mixture at approximately 14.7 which is normal and needed. At hot running temperature and hot ambient temperature it allows less air into the combustion chamber to keep at 14.7 as air is heavier when cold and retains a higher mass index. The intake air is monitored by the MAP and exhaust is monitored by the 02 sensor all running in harmony.
5th. When you load up the motor or load up the voltage used for the system normal wattage is not sufficient to run the system. The IAC opens slightly and the TPS controled by the PCM increases fuel delivery to retain the 14.7 stoichiometric air/fuel mixture. This both takes the load off the motor and increases alternator output for the load on the electrical system. The intake air is monitored by the MAP and exhaust is monitored by the 02 sensor all running in harmony.
6th. Your Check Engine light is illuminated indicating an issue. You might want to look to see what the issue is.
*noted*-----P0138 1/2 O2S Shorted To Voltage----is a 02 code and you need to change out the pre-cat 02.
7th. You disconnect the IAC an not expect it to idle low or have issues.....hmmmmm....It almost stalls because you disconnected it and it can't tell the PCM to add more fuel!.....Well of course it's going to stall! Then you add even more load and you expect the PCM to compensate even though the IAC is disconnected? If it is doing what yours is doing then the user has absolutely no input NOT a incorrect, floating voltage, or intermediate reading.
8. You state that your IAC is bad and in need of "new one" then tell others that if it acts like yours before it is unplugged then it's good.....Um....wtf?
Not to drive ya into the ground on this one, but where did you learn this stuff cause you are all over the place? You don't fully understand MPI injection? Then you tell people that yours is running properly?
2nd. The air box stuff and the "whatever this is called that sits over the throttle body" that you take "loose" is called an Air Hat, Air Box, and Intake tubing.
3rd. The PVC Crank Case Breather is 2 seporate and distinct things. You have a PCV valve that goes into the Intake Manifold for vacuum. This is located on the valve cover and each year is different. On the opposite side is the crank case breather line and it attaches to the Air Hat on the back side. This is so filtered air can inlet into the crank case and be drawn out on the other side of the motor to remove the monoxide from blow-by so it does not acidify the oil.
4th. The IAC valve does not say how much air goes into the throttle body. The MAP sensor detects the air volume and the IAC also air to go around the butteryfly on the throttle body as it is closed. During cold start or cold running the IAC opens more to allow more air to go by keeping the stoichiometric air/fuel mixture at approximately 14.7 which is normal and needed. At hot running temperature and hot ambient temperature it allows less air into the combustion chamber to keep at 14.7 as air is heavier when cold and retains a higher mass index. The intake air is monitored by the MAP and exhaust is monitored by the 02 sensor all running in harmony.
5th. When you load up the motor or load up the voltage used for the system normal wattage is not sufficient to run the system. The IAC opens slightly and the TPS controled by the PCM increases fuel delivery to retain the 14.7 stoichiometric air/fuel mixture. This both takes the load off the motor and increases alternator output for the load on the electrical system. The intake air is monitored by the MAP and exhaust is monitored by the 02 sensor all running in harmony.
6th. Your Check Engine light is illuminated indicating an issue. You might want to look to see what the issue is.
*noted*-----P0138 1/2 O2S Shorted To Voltage----is a 02 code and you need to change out the pre-cat 02.
7th. You disconnect the IAC an not expect it to idle low or have issues.....hmmmmm....It almost stalls because you disconnected it and it can't tell the PCM to add more fuel!.....Well of course it's going to stall! Then you add even more load and you expect the PCM to compensate even though the IAC is disconnected? If it is doing what yours is doing then the user has absolutely no input NOT a incorrect, floating voltage, or intermediate reading.
8. You state that your IAC is bad and in need of "new one" then tell others that if it acts like yours before it is unplugged then it's good.....Um....wtf?
Not to drive ya into the ground on this one, but where did you learn this stuff cause you are all over the place? You don't fully understand MPI injection? Then you tell people that yours is running properly?
Hall Of Fame
Joined: Jun 2005
Posts: 14,228
Likes: 19
From: Riverton, UT
I see,
Like I said I'm not dissin on ya or anything, just layin down the facts. Ya know I wish somebody would make a video on how to properly clean the whole Throttle Body incuding the dissasembly and tuning as well.
Like I said I'm not dissin on ya or anything, just layin down the facts. Ya know I wish somebody would make a video on how to properly clean the whole Throttle Body incuding the dissasembly and tuning as well.
THE ULTI-MOD
Joined: Jan 2007
Posts: 19,797
Likes: 36
From: Union NJ
someone get me a good video camera, and be willing to donate some downtime for their 5.x series D and ill get one for 4.7 and one for 5.x series 
Trending Topics
Hall Of Fame
Joined: Jun 2005
Posts: 14,228
Likes: 19
From: Riverton, UT
Now that would be SWEET!
Now you wouldn't need a really good camera to do it. Personally, I think you want a good camera is because the camera always adds a few extra pounds and you want to edit it.....ROTFMAO
Now you wouldn't need a really good camera to do it. Personally, I think you want a good camera is because the camera always adds a few extra pounds and you want to edit it.....ROTFMAO