Hello,

I have a 2001 Dodge 1500 pickup with the 3.9L V6 engine. It has approximately 60,000 miles.

The problem is the truck idles fine when it starts up, but after about 5 mins or so when idling, the truck starts to shake and idle low (about 300-400 rpm). The engine does not stall. I can hear a sucking noise from the Idle Air Control (IAC), and it gets louder. Eventually, the noise, rough idle, and shaking disapears and the engine runs very smooth.

This also occassionally happens when the truck is idling at a stop in drive position. When this happens and I try to accelerate, the truck hesitates and I hear backfiring from the exhaust. The truck loses power and will not accelerate. I have to pull over and try to baby the truck to return to normal. I still hear the sucking noise from the IAC when this happens.

I have gotten a Check Engine Light with the P0132 code (O2 signal wire shorted to voltage) a couple of times. I checked the O2 wiring before the catalytic converter, and the wire seems fine. I have replaced IAC, spark plug, ignition wires, throttle position sensor (TPS), and fuel pump. What could cause this problem? This is happening more often, and it is starting to irritate me. I would like some suggestions. Thanks.

What could

 

The IAC leaking could definitely cause a rough idle as you described. To my knowledge there is only 3 things that could cause a leak or suction noise from the IAC and that is that the Oring that seals it to the throttle body is bad allowing air to get sucked it when it shouldn't be. The IAC itself being damaged as in a hole straight through it allowing air to pass through its body, or the throttle boddy its self being damaged. And to be honest I've really never heard of any of those three scenarios occuring.

I would check all of your vaccuum lines and make sure to replace any of them that may be cracked or dry rotted. I'm curious how you identified that the IAC is whats causing the sucking noise? If it turns out not to be coming from the IAC, TPS, MAP, or throttle body which all 3 sensors are bolted to the throttle body meaning it would usually be hard to tell where it was coming from without something being visibly wrong. If it turns out to be none of those things then you may need to pull the intake manifold and replace the gasket that seals the plenum plate to the bottom of the intake. An Easy way of checking to see if this is a possible issue is to remove your throttle body and shine a light inside the oppening on top of the intake manifold to look for oil inside the intake... this plate that I speak of is dirrectly above the lifter valley and due to where it is with the oil and heat cycling through that area sometimes that gasket will go bad and will cause the same condition you've described.

But do not do what some people would do and just jump straight to pulling off parts when it may in fact be nothing more than a slightly cracked piece of hope that is sold for around $1.00 per foot hope this is helpful. let us know what you find!

 

if you've already replaced IAC and TPS with no change, you need to look elsewhere.
the loud sucking sound from the IAC is just a symptom of your problem, where the IAC is opening up more to try and keep it running.

you have a CEL code regarding 02. don't ignore it, as its likely the root cause of the problem. either the 02, the wiring, or the pcm. the 5 min warm up is significant. when cold, the truck runs a rich mix in open loop. after warm up, in closed loop, the pcm uses the 02 signal to tune the fuel ratio. your's is wandering too far rich or lean.

if you haven't yet replaced the front 02 sensor, do that. NTK/NGK has good reputation. be sure and get the ones with oem plugs, not universal, to avoid potential wiring problems. it will have a long lead and connect on top of the trans, which eliminates any existing damaged wiring.

 

Thanks for your replies!

When I replaced the IAC, I made sure the o-ring fit properly so there was no air leak. When I heard the air sucking noise, I placed my finger in the hole and that is how I found where the noise was coming from. I just replaced the MAP sensor today and experienced the same problem. So off to something different.

For the gasket that seals the plenum plate to the bottom of the intake. Are you talking about the gasket where the intake plenum and the block meet or the throttle body to the intake plenum? I replaced the gasket where the plastic airbox mounts to the throttle body? You mention the lifter valley, but I don't know where that is? If you are talking about the gasket between the intake plenum to the block, there is going to be some work involved. Also, I did look through the intake plenum and there is some oil residue inside the plenum but that is normal from what I have seen in other vehicles.

I am thinking about replacing the O2 sensor next. I looked at the old connector and found that mine is a round type plug. Looking at the NGK/NTK O2 sensor lookup on there website, I found that the one for the 2001 is 23139 which has a square type connector. I also found on this forum that the 2001 had two different type of O2 sensors. The one with the round plug, which I have, is 23151. Could you guys confirm this is the correct one? I am going to buy this online and don't want to order the wrong one.

Let me know what you guys think and shoot me some more suggestions to my problem. Thanks!

 

Quote: "Also, I did look through the intake plenum and there is some oil residue inside the plenum but that is normal from what I have seen in other vehicles. "

Oil inside your intake is never normal my friend. Not sure if you've ever pulled an intake manifold off a V6/V8 or not but I'm thinking not by your response to where the lifter valley is at. When you take off an intake manifold the area you will see under it (in the case of a pushrod engine... which is exactly what you have) that houses your valve lifters and pushrods is what is refered to as the lifter valley. The Intake Manifolds on the Dodge 3.9L, 5.2L, and 5.9L are called beer barrel intakes due to their shape. The intakes for the 5.2 and 5.9 are in fact the same part. So basically, they used a V-6 intake manifold and a V-8 intake manifold in these trucks. If you take off one of these intake manifolds and flip it upside down you will see a stamped steel plate that bolts to the bottom of the intake manifold this plate is known as the plenum chamber plate it seals the bottom of the intake manifold/plenum chamber. Plenum chamber describes that big open space inside of the intake manifold.

The gasket between the plenum plate is meant to stop air, oil, and any other substance from being sucked into the engine from any place other than through the air filter and throttle body which are mounted on top of the intake manifold. Which means that if you have oil inside of there you have a leak that is allowing the engine to suck the oil into the intake manifold which is not supposed to happen.

Now just for clarity's sake, when i said to check for oil inside the intake manifold I meant to make sure that you do not have black liquid pooling up in the bottom of the intake manifold. I was not referring to the black residue that forms on the interior of the intake manifold, this residue will appear to be dry not wet and runny. If you have black liquid in their that is in no way normal my friend. If it's sucking oil into the bottom of your intake manifold due to that gasket leaking then the computer is gonna be all screwed up because it's basically going to try to compensate for what it is reading as a vaccuum leak/ false high air temperature reading. This false air temperature reading is caused by the fact that the air temperature sensor is mounted on the side of your intake manifold. Since hot air is being sucked from the crank case (which is the open area of the block where the crankshaft is spinning) and thru the lifter valley and into the plenum through a leaking gasket the sensor will be sending false signals back to the computer telling it that things are too hot and that fuel delivery needs to be adjusted accordingly which can create a lean condition in an attempt to get things back to the factory parameters...

Can you see why Oil inside the Intake Manifold is an indication of something bad going on? Other than thru that gasket and thru the throttle body there is only one other way for a puddle of oil to form inside the intake that I can think of and that is if it is coming back out of the cylinder head intake ports (which means its being blown back thru the valves Which means huge problems. Thankfully that is very very highly unlikely!) However, it is not unheard of that it would be coming thru that gasket if its not sealing properly! It is a paper gasket after many heat cycles and long exposure to oil from the lifter valley along with the other crankcase gasses it will deteriorate and allow things to leak.

Again, there is a Stamped Steel Plate that bolts to the bottom of your intake manifold and to replace the gasket that seals the 2 parts together you must pull the intake manifold off of the engine, flip the intake manifold upside down and unbolt the plate from the bottom. There is a torque sequence and torque rating for each bolt that needs to be followed when re-installing this plate to the bottom of your intake! A new plenum gasket and a new intake manifold set is usually a cheaper fix than the O2 sensor.

And the fix is what I would hope you are after and not just throwing parts at it and hoping one of them fixes it which is what I've seen and made a living off of in my past. Nope, I dont feel guilty about that either because I was always a good boy and advised my customers the same way I am you now so no guilt trips about making a living off of people just throwing parts at their vehicles lol!

Now the post about the O2 sensor as far as brands... I too would recommend one of the direct fit ones. However, since Bosch made your original O2 sensor and they have not been known for going bad frequently I would stick with a Bosch. You can find them at NAPA.

However, I'd hold off on the sensor though, until you are absolutely sure that the sensor is actually bad. I used to work at NAPA and have seen many people replace sensors thinking it would fix their issue only to find it didn't and then want their money back because it didn't do the trick. You've already replaced the IAC and the MAP sensors with no luck in fixing your problem. Sensors can usually be tested to verify if they are bad or not.

It has always been my experience that some underlying problem is what caused the sensor to go bad and if it goes unrepaired it will continue destroying sensors. Don't assume that a code indicates a bad sensor. Often times it only signifys a reading that is not within parameters which means no matter how many times you replace the sensor it will never fix the problem because something else is what is causing the sensor to have a bad reading. With a little patience and some good old fasshioned troubleshooting you can verify bad sensors and fix what is causing them to go bad. I think I have given you at least one candidate that could cause the O2 sensor to get some false readings and that is namely the Plenum Gasket allowing hot air into an area it is not meant to be which starts a chain reaction causing the air temp sensor to tell the computer to stop flooding the engine with fuel which would create a leaned out situation causing a stall or near stall out condition and also some codes to pop up about your O2 sensor.

Personally I'm not a fan of ordering parts online but I suppose that would be because I've been behind that counter and have heard just about every complaint you can think of about different parts manufacturers. Plus theres 5 different parts houses in my town. Wasn't often I had to warranty a NAPA Part but I had most of my customers turned into my customers by the parts they were purchasing and frequently changing because they got it else where. If a day went by without a new customer coming from another parts house fed up with buying something due to it having a lifetime warranty that was more like a 2 week warranty because they changed the part every 2 weeks I had had a very very slow day... I can still count how many days we had that were that slow on one hand.

NAPA usually trains their people very well and usually will have the best parts available. Plus if the part goes out during it's warranty period just take it back along with a copy of your receipt and you'll have a new one usually the same day and you're back on the road the same day! Instead of the several days it will take an online source to send out a replacement part. Sure you maybe able to save a few bucks with an online source but if you ever need it warrantied out you just lost those bucks during the time you spend with your vehicle down and awaiting a replacement part from the online source. Which to me Personally spells No Bueno!!!

Keep us informed and let us know what you find we all are feeling the pinch in the wallet area and are here to help!

 

Please keep us updated Maxpusher as I am having the exact same symptoms with my truck. When mine hesitates during acceleration, if I let completely off of the throttle for about 10 seconds and then mash into the throttle, the problem goes away usually for days or weeks at a time. This problem is very intermittent and because of this I have not yet taken it to a Dodge dealership to have it scanned with the DRBIII tool. They told me they may not be able to diagnose it so I have been researching this forum for about 2 months now. I posted a thread and had another problem with this problem, and that problem was fixed but it seems to be affecting my transmission shifts from 1st to 2nd as well. Some of the other forumees were kind enough to give me some wonderful advice and they suggested that I replace the TPS as well. I have not replaced that yet and it seems that may not be the problem as you replaced yours and still have the problem. My biggest fear is that it is the plenum plate gasket, but either way, definitely keep us informed on the outcome and I will provide my results as well. I know I should test my TPS before replacing it, but it is almost easier just to replace it and I found one with a lifetime warranty for $50 so I will probably replace it anyways. Thanks for sharing your problem, good luck in diagnosing it and fixing it, and I look forward to your update.

 

Thanks for replying. I will let you know what I find. I am going to do some tests with O2, crankshaft, and camshaft sensor to see if these are working properly. I have the Chilton and Hayes manuals, and they should how to test these. I will update on what I find.

 

Any updates? Find out whats wrong with it yet?

 

Well, I finally got the problem fixed last weekend. I did some tests using the manuals. I tapped into the O2 sensor plugs and found very little voltage. I bit the bullet and ordered the NTK O2 sensors from Amazon for about $46 and replaced it. Now, the truck runs with no problems. It is kind of strange that the CEL for the O2 sensor did not stay on longer. I appreciate all your help.

 

Glad you got it fixed!