Intermittent High or Surging Idle - Dodge Magnum 5.9L V8

[DonCurley]

I have a Dodge Magnum 5. 9L V8 (from a 2000 Dodge Durango) that was swapped into my 2000 Jeep Wrangler TJ back in 2006. It took me a while to figure out what was specifically wrong, but about 5,000 miles ago, I suffered the dreaded plenum plate/gasket failure and got a lot of crankcase oil into the intake. I have now completed the work to pull my intake manifold and upgrade the crappy factory plenum plate with a beefy 1/4" aluminum plate from APS Precision, along with the newer design plenum plate gasket. The good news is that my 5. 9 is running great now with plenty of power, no pinging, and no more repetitive P0171 "system too lean (bank 1)" fault codes.



However, I am still having an intermittent problem with a high (~2000 RPM) or surging idle about 25% of the time after the engine is up to operating temperature and I have come to a stop. I have no idea if it is the cause, however, I am wondering about the condition of the original idle air control (IAC) motor unit on the back side of my throttle body (which I carefully cleaned but did not replace). If the IAC is acting up, could that cause my intermittent high or surging idle?



If it's not the IAC, would any malfunctions with the following contribute to my intermittent idle problems?



- Intake manifold air temperature (IAT) sensor

- Throttle position sensor (TPS)

- Manifold absolute pressure (MAP) sensor



If anyone has any ideas as to what might be causing my idle issues, I would sure appreciate getting the input.



Thanks,

Don

 

[leaky gasket]

O2 sensor may be lazy from the oil.

 

[DonCurley]

Just curious, but how would a "lazy" O2 sensor cause an elevated or surging idle? Beyond that, can O2 sensors be effectively cleaned or do they just have to be replaced when they get fouled?

 

[Wayne M.]

I have a Dodge Magnum 5. 9L V8 (from a 2000 Dodge Durango) that was swapped into my 2000 Jeep Wrangler TJ back in 2006. It took me a while to figure out what was specifically wrong, but about 5,000 miles ago, I suffered the dreaded plenum plate/gasket failure and got a lot of crankcase oil into the intake. I have now completed the work to pull my intake manifold and upgrade the crappy factory plenum plate with a beefy 1/4" aluminum plate from APS Precision, along with the newer design plenum plate gasket. The good news is that my 5. 9 is running great now with plenty of power, no pinging, and no more repetitive P0171 "system too lean (bank 1)" fault codes.

However, I am still having an intermittent problem with a high (~2000 RPM) or surging idle about 25% of the time after the engine is up to operating temperature and I have come to a stop. I have no idea if it is the cause, however, I am wondering about the condition of the original idle air control (IAC) motor unit on the back side of my throttle body (which I carefully cleaned but did not replace). If the IAC is acting up, could that cause my intermittent high or surging idle?

If it's not the IAC, would any malfunctions with the following contribute to my intermittent idle problems?

- Intake manifold air temperature (IAT) sensor
- Throttle position sensor (TPS)
- Manifold absolute pressure (MAP) sensor

If anyone has any ideas as to what might be causing my idle issues, I would sure appreciate getting the input.

Thanks,
Don

This has been up a while. Have you found the problem? I really doubt any of the sensors mentioned are malfunctioning (except the IAC). Any irrationale would set a code one way or another. You really need a good scanner to look at the parameters such as fuel trim, IAC counts, O2 graphing and such. I've been spoiled by the DRB (chrysler factory scan tool), and I find having that info is priceless. I'm going to guess that you still have a vacuum leak, or the IAC is hanging. Knowing the fuel trim would tell the tale. Sounds like a nice swap. Pictures?

 

[btggraphix]

This has been up a while. Have you found the problem? I really doubt any of the sensors mentioned are malfunctioning (except the IAC). Any irrationale would set a code one way or another. You really need a good scanner to look at the parameters such as fuel trim, IAC counts, O2 graphing and such. I've been spoiled by the DRB (chrysler factory scan tool), and I find having that info is priceless. I'm going to guess that you still have a vacuum leak, or the IAC is hanging. Knowing the fuel trim would tell the tale. Sounds like a nice swap. Pictures?

Hi Wayne - Don was a good friend of mine; he passed away suddenly early last year. My wife and I ended up buying his Jeep from his wife this fall, and with it, inherited the issue he was trying to solve. It is particularly difficult since although he had a lot of records on the Jeep, there are way more unanswered questions than answered. I'm pretty mechanically inclined, but honestly I've never really learned much about the computers and reprogramming. Or Frankenstein engine swaps since I was in high school and there weren't really much in the way of computers.....

I have begun investigating the issue. Yes, there is a bit of a surge at idle still, but I am now seeing the P0171 code coming up with the CEL on that Don had thought he had solved. Those are the two symptoms mainly (although it does seem to ping a bit at higher throttle positions on highway hills.)

I am going to keep this first post to a minimum; I'm not even sure if this thread is too old for me to update it or not.

First, from what I understand, Don DID end up changing the throttle body, as well as the O2 sensors. His wife told me his next theory to test was the fuel pump.

I took it to a good mechanic I use to diagnose the codes and give me suggestions. I'll post an update assuming this post "makes it".

 

[btggraphix]

OK, well that made it so I guess the thread wasn't too old to update. Below is the full write-up of what my mechanic found/did during the "first pass". I have always thought one of the best things about this mechanic is that he does a very good job of documenting everything, and for an issue like this, it is as valuable as any wrench turning.

Goal: Check over as it is new to customer. The idle surges and is erratic; the check engine light is on.

Diagnosis:

Trouble code P0171 set as a hard failure for the fuel system running too lean, no other hard failures or pending codes.

The idle does vary in speed.

Monitoring scan data found the throttle position sensor voltage would vary at idle even when the throttle was never touched.

These systems of this vintage have a long record of TPS failures in this manner causing exactly this problem.

All connections and voltages at the sensor are good.

The long-term fuel trim #’s are fine off idle, averaging +3% under normal loads, but climbs to +25% at idle.

We cannot find any vacuum leaks, externally or internally on the motor that would cause this.

Furthermore the upstream O2 sensor shows good fuel control at all times, even when the trim #’s are at 25%.

If the system were in fact that lean and the PCM really did have to add that much injector pulse width to get the mixture correct, the upstream O2 sensor should be reading below 300mv constantly.

The trim #’s will go into the preferred range of operation [+/-5%] as soon as the throttle is moved as little as 2%.

If there was a vacuum leak anywhere on the motor to cause this big of a lean condition, it would still be evident at 1-2% throttle opening.

Thinking the errant TPS readings will confuse the PCM as to whether or not the vehicle was really idling, we replaced the TPS and performed a relearn of the TPS settings and the fuel trim.

The PCM readily accepted the new TPS relearn, but we could watch the idle fuel trim #’s climb from 0 to +25% again for no reason.

Again, the TPS readings would vary on the scanner when the throttle was never touched.

Backprobed the TPS connector with the scope to monitor Power, ground, and output voltages; all were rock steady even when the position voltage varied on the scanner.

The fuel pressure was a steady 48PSI at all times during testing.



We strongly feel that all of the above conditions are caused by the aftermarket programming done to the PCM.

We have seen discrepancies in input to output correlations many times before with non-stock programming in a stock PCM.

Spoke to owner about our findings; decision was made to get it through emissions before tackling any new or used PCM possibilities or programming.


There was a tag on the PCM from B&G Chrysler Specialists who apparently did the programming.

Daimler P/N P56040368AE, S/N 25GCP07F14, module S/N TEH130007V16

The following is programmed info in the PCM:

P/N 56040410AG, Federal Emissions, Chassis-RWD, A/T, Aspiration-NATASP, Injection-EFI,Fuel Unleaded, Year 2000, Engine 5.9, Fan-none,Hardware-JTEC+,Body-BR, Trans-4AT

 

[btggraphix]

So his thoughts were to either, try to find a stock PCM to test or to attempt reprogramming the existing one. He doesn't do programming (he is pretty much an OEM guy.) Soon after, Don's wife came across some more Jeep parts, including a box labeled 2000 PCM for Jeep TJ with 2000 Dodge 5.9L. It might have been the one that came with the engine when he purchased it, or it could have been the OEM from the Jeep...wasn't sure. But I took it back to my guy to have him try swapping it out and see what would happen. Not much as it turns out......the PCM was in fact from a Dakota R/T with a 5.9L, but it includes the Central Timer Module [CTM] and the Vehicle Theft Security System [VTSS] which would shut it down after 2 seconds of running, and lock-out after 3 failures for 20 minutes. I'll type up the diagnosis text for this round in a bit. I'm getting closer to my "what should I do now?" point, honest!

 

[btggraphix]

OK, so, here's what my mechanic came up with, when trying to install the PCM from (apparently) a 2000 Dakota R/T:

Installed the “extra” PCM.
The vehicle would fire up and die.
Data parameters showed the PCM would not allow the injectors to operate after 2 seconds of running.
Repeated this 3 times thenn would not turn on the injectors at all until the theft deterrent system times out
The problem here is the Jeep was not setup from the factory with a Central Timer Module [TCM] that tells the PCM it is not being stolen and that all is OK for engine operation.
The Dodge Dakota R/T was equipped with this and much more; this is what the OCM is programmed to see but is not on the data stream on the Jeep.
The theft deterrent portion of the “reprogrammed” PCM has been erased; this is why it fires right up and runs when it is installed.

We ran the numbers of this “extra” PCM through the dealer and it came back as a PCM for a Dakota/Durango RWD, Automatic R/T model with federal emissions programming.
This concurs with the Programmed Module Info in the PCM that can be accessed with the scanner.

Interestingly enough, the working PCM’s numbers were run through the dealer at the same time as the “extra” one and they came back for a 2000 Ram 1500 Pickup with a 5.2L engine, Auto, federal emissions programming

 

[btggraphix]

So that's all the info I have. It seems like Don must have gotten the Dakota R/T PCM to use with the engine....it may have even come WITH the engine when he did the swap. But for some reason, they instead used a PCM from a 2000 1500 pickup for some reason; maybe because B&G or the engine builder thought that it would be easier to reprogram without all that CTM/VTSS stuff? They apparently "told" the PCM it was from a Dakota R/T with a 5.9L.

It seems clear that there is NO stock PCM that would work without programming of some kind, at the very least to wipe the CTM/VTSS. Unless there is some flavor of a pickup that came with the 5.9L engine but none of that other stuff........so it seems to me I am left with trying to find a magician with PCM's.

I guess unless I get some more suggestions or more information, my next step is probably to try to get a hold of B&G since they did the programming on the "nearly" working PCM. I'm pretty leery of reprogramming the one I have that actually works (other than the surge/idle/P0171 issue.) I guess since the "extra" I have is in fact for a Dakota R/T with the 5.9L it seems like that would be the ideal one if we can get it to forget about the CTM/VTSS.

If you actually made it through all that description and have any thoughts, please let me know. It would be greatly appreciated. Wayne, I'll try to post a few pictures of it soon too.
To stoke your interest in this sweet Jeep, if you want to see some pictures from a trip we did with Don out in Moab back in 08 or so, check them out here

 

[Wayne M.]

Hey! Wow, so sorry to read what happened. I guess you're gonna carry on this project. Ok. I see the fuel trim numbers, and if this PCM has really been "tuned" I still think there's a vacuum leak of some sort. Can you tell me exactly how a vacuum leak was eliminated from the DX?

 

[btggraphix]

Hey! Wow, so sorry to read what happened. I guess you're gonna carry on this project. Ok. I see the fuel trim numbers, and if this PCM has really been "tuned" I still think there's a vacuum leak of some sort. Can you tell me exactly how a vacuum leak was eliminated from the DX?

Well, that was the first thing he tested/worked on/filled me in on and it was a pretty long conversation.....on that part of the conversation I remember thinking "good, a couple of mine friend's first comments were about a vacuum leak". I think he told me how he did it with a second mechanic and it seemed reasonable to me. I've always used carb cleaner or starting fluid depending on what I had handy back when I was delivering pizzas in college and driving beaters. I also remember being curious about how he checked the internal vacuum in the engine which I hadn't ever heard of before. So as much sense as it would make, I'm pretty confident he did a thorough job on testing for a vacuum leak.

He made several comments that specifically relate to vacuum:

1) We cannot find any vacuum leaks, externally or internally on the motor that would cause this.

2) Furthermore the upstream O2 sensor shows good fuel control at all times, even when the trim #’s are at 25%.

3) If the system were in fact that lean and the PCM really did have to add that much injector pulse width to get the mixture correct, the upstream O2 sensor should be reading below 300mv constantly.

4) If there was a vacuum leak anywhere on the motor to cause this big of a lean condition, it would still be evident at 1-2% throttle opening.

So while I won't say it isn't possible he missed a vacuum leak, he definitely looked for them and his logic on what you would expect if there WAS a vacuum leak seems sound. If you think I should or it would help you theorize, I can certainly check in with him and ask again. I did have a couple of questions that came to my mind after re-typing his DX. I do appreciate your chewing on this problem, thanks!

 

[fest3er]

He changed the throttle body. But are the shafts/bearing sound? Shaft play can cause idle problems. My old F150 couldn't hold idle for a long time. Never mind trying to hold it, just trying to *reach* 1200 RPM for the pollution test was almost impossible. Keep adding throttle and it would keep slowing down. Until it just about reached the target RPM and it would suddenly race. Worn shafts. One of the reasons I decided against buying another gasser.

Get an ohm meter and check resistances between B- and various ground points and other places that should be grounded. When cold and when warm/hot. Explain resistances higher than a few ohms, significant differences between when cold and when hot, and varying resistances. Or use a voltmeter while running; measurements higher than a few hundred mV must be explained, as must varying voltages.

 

[fest3er]

[Google Chrome re-submitted after clicking 'back'.]

 

[Wayne M.]

Well, that was the first thing he tested/worked on/filled me in on and it was a pretty long conversation.....on that part of the conversation I remember thinking "good, a couple of mine friend's first comments were about a vacuum leak". I think he told me how he did it with a second mechanic and it seemed reasonable to me. I've always used carb cleaner or starting fluid depending on what I had handy back when I was delivering pizzas in college and driving beaters. I also remember being curious about how he checked the internal vacuum in the engine which I hadn't ever heard of before. So as much sense as it would make, I'm pretty confident he did a thorough job on testing for a vacuum leak.

He made several comments that specifically relate to vacuum:

1) We cannot find any vacuum leaks, externally or internally on the motor that would cause this.

2) Furthermore the upstream O2 sensor shows good fuel control at all times, even when the trim #’s are at 25%.

3) If the system were in fact that lean and the PCM really did have to add that much injector pulse width to get the mixture correct, the upstream O2 sensor should be reading below 300mv constantly.

4) If there was a vacuum leak anywhere on the motor to cause this big of a lean condition, it would still be evident at 1-2% throttle opening.

So while I won't say it isn't possible he missed a vacuum leak, he definitely looked for them and his logic on what you would expect if there WAS a vacuum leak seems sound. If you think I should or it would help you theorize, I can certainly check in with him and ask again. I did have a couple of questions that came to my mind after re-typing his DX. I do appreciate your chewing on this problem, thanks!

Roger that, but my question still is, how/ what method did he use to eliminate vacuum leaks? Not always an easy proclamation! I don't know much about customizing a fuel map and especially what was done to that one, but I know the basics. If one "block" covers idle to- say 1200RPM, and the fuel was set too lean in that block, then yes, you will have a bad trim at idle, then once you get out of the block and the next block is acceptable, you will get a better trim. It'll be like flicking a switch. Yes trim can respond that fast when looking at it on a real time scanner.

Neal, I remember those Ford SEFI engines. The older electronics, and especially the actuators were a bit slow to compensate causing headaches like holding a no load engine speed.

 

[btggraphix]

Fair enough Wayne. I'll find out. It does seem like if it was a problem with the "block" up to some RPM, if the engine goes into a surge (say from 800, to 1100) that would kick it into that next block. The reality is that cracking the throttle just 1-2% the issue goes away, even though the increase from the little throttle movement only barely ups the RPM. In other words, it doesn't seem like it relates to RPM, only throttle position. But of course, it may be there is one "block" for idle and another if there is any throttle input at all. I just don't know much about how these things are programmed. In fact, I troubleshoot software/networks for my real job and it does sort of smack like an electrical or software issue somehow....so I kind of like Neil's idea about a bad ground. One of the first buddies of mine I described the issue to and he immediately mentioned having had a Subaru (I think it was) that he messed with that had an idle issue and it did turn out to be a bad ground. Everything on this Jeep is spotlessly clean (or was when we bought it) and all the electrical looks very well detailed, cable-tied and brand new.....battery in a new AGM and the ground strap itself is really big and high-end looking. There are big off-road lamps, winch, air-compressor stereo etc. and I don't see any dimming to the lights at all when idling.....but those don't really mean anything.....might just convince me to ignore something like a bad ground. I'm going to see if I can get a chance to run through some testing this weekend on that because it'll be pretty easy and I don't remember my mechanic mentioning checking ground at all in his tests.

You know, one electrical oddity we came across....was when we hooked up the Jeep to our truck to flat tow it back to Colorado, we tried to hook up Don's brake buddy system. There is a 12v cigarette receptacle he put in down near the pedals. When we plugged in the brake buddy, the unit's lights came on, but the compressor didn't turn on. I messed around for a while and then ended up giving up and blowing it off (we have a 19,000 truck and camper combination....a Chevy Kodiak + Lance camper and the brake buddy isn't really necessary.) But for grins, right before we took off, I plugged it in to the lighter in my truck, and the compressor kicked on right away. I only mention that because it seemed pretty odd....SOME power was coming to it since it lit up, but something about the quality or amount of power was preventing the compressor from coming on. Probably not related, but the only electrical oddity I've noticed so far.

We are driving it as a daily driver at the moment (we fight each day who gets to drive it!) and the CEL has been kind of going on at times, and not others. It replaced my wife's 4Runner, so she wins the argument usually.

I'll update this thread when I learn or do more. Thanks again.

PS: Neal, are you suggesting the bearings/shaft on the throttle body? Seems like that would cause a variety of behaviors, not one so specific and limited to ONLY no throttle idle???

 

[fest3er]

Yes. If the 'bearing' area is worn, the throttle plate can stick, it can jump, the plate can open with the pedal then suddenly open a lot more when the shaft changes position. With modern systems, tiny changes in plate opening make for larger changes in RPM.

Also, remember that the throttle plate closes completely at idle; idle air is then totally controlled by the IAC (a small passage around the throttle plate).

 

[fest3er]

Yes. If the 'bearing' area is worn, the throttle plate can stick, it can jump, the plate can open with the pedal then suddenly open a lot more when the shaft changes position. With modern systems, tiny changes in plate opening make for larger changes in RPM.

Also, remember that the throttle plate closes completely at idle; idle air is then totally controlled by the IAC (a small passage around the throttle plate).