Hello guys, I came across this forum today when looking for some answers to my peculiar issues on the 99 durango 5.2. Basically to give you an idea of the durangos history, it was owned by my father who maintained it very well, but it has been used to tow heavy boats and drive as a utility vehicle of course. It has been GREAT up until now, besides the rust.

Unfortunately I now have inherited the durango, and its problems. I use it to tow jet skis and get me around in the winter, so it does not need to be "perfect" but it does have to work!! And right now I am beginning to question its usable life. I genuinely hope some people here have had these issues before, and maybe they are related.

First problem is the engine. The idle speed will not settle to the normal 600rpm, it is always 700-800 rpm, but very rarely surges. Rather, it has a major hanging idle. This issue is directly related to a few other issues I believe. While driving, of course the hanging/high idle causes it to accelerate when it should be "coasting". This brings me to my major issue. If I apply any heavy acceleration, or kick down acceration the hanging idle problem become much worse, and then the transmission will become stuck in gear.

This transmission problem seems to be related to the engine problem. This is a typical scenario:

1. Driving normally, shifting normally
2. Apply heavy/full throttle to get out of a tough intersection
3. Now transmission will not shift out of 1st until the redline
4. Now in second, the transmission will not shift into 3rd until close to the redline
4. Now in 3rd the transmission almost immediately goes into overdrive and the engine high idle seems to settle down to a more reasonable level
5. Once I slow down to a speed below lets say 40mph, the transmission abruptly shifts down into the lowest possible gear, typically 2nd, and remains stuck until I accelerate again to the redline area

This process repeats it self EVERY single time I apply heavy throttle, and after about 15 mins of driving and forcing it to shift using my above process, it eventually will start to shift normal again. Normally I would say this was mechanical, but here is the bizzare part. I think it is safe to assume that the issue is related to engine load/RPM in gear right?

Wrong!! Lets say I stop and the durango was just shifting perfectly all day. Now if I engage neutral and rev up the engine near the redline again, but in neutral and then put it back in drive and pull away, the same terrible shifting issue appears again! This is the strange part about it, I cannot say for sure what is causing the transmission to shift like this, all I can say is it has been doing this for a year now.

The hanging idle issue only started a few months ago when I blew a hole in the muffler somehow on the highway. I am replacing the muffler this weekend and I am guessing it is somewhat related to the muffler since it happened IMMEDIATELY after I heard the muffler break open (rusted as heck). Just to be safe I replaced the IAC motor, PCV, IAT sensor, and TB gasket. None solved the problem. Just to add a little more information to the information overload I just typed, if I reset the PCM the engine will run BEAUTIFULLY and idle beautifully for about 20-30 mins, until the adaptations take over and begin to make it run like crap and high idle again.

I have never adjusted the bands, I did not know how, nor did I know they were adjustable. The transmission has had its fluid changed every 15k miles since new. We literally have had ONE problem with this durango since it was new, and that was the speed sensor going bad from too much salt water. I love this machine and hope to get it back into normal operation for years to come. 122k miles by the way. Any advice on where to start!!!!?????

Thanks to anybody who read through this huge post. I can put some cliff notes up for people who don't have time to read that much!

 

If replacing my blown muffler doesn't fix the high idle problem, I forgot to mention what my other thoughts were. I suppose a TPS could cause the high idle problem, although I doubt it would be bad without a code, and that wouldn't explain why the idle problem doesn't exist after you reset the PCM.

The other thought was maybe a bad MAP sensor but not throwing a code. That could also effect how the transmission shifts correct?

Is there any vaccum related controler for the transmission? Or is that what the MAP sensor does?

Looking forward to hearing some opinions.

 

One other thing I noticed is that the idle picks up 100rpm when the ac compressor kicks on. Is that normal? Im really hoping to get this resolved this wekeend. Can a MAP sensor cause these issues?

 

Nobody has any ideas lol? I will report any findings tomorrow, but before then it would be helpful to at least know what a normal idle RPM should be. 600? 700? I am at 700 now, but of course it randomly hangs, which causes the tranny not to downshift when I am braking and makes the problem seem much worse.

 

typical idle for any v8 is 500-700 rpm, turning on the a/c will raise the idle by ~200 rpm

 

Okay cool, I am on the high end of that. I wonder if the computer is overcompensating the RPM increase when the compressor cycles on. I feel it when it compresser turns on while I am slowing down.

Whatever is causing the high idle/hanging idle is quite erratic. It could be the TPS I guess. So I might replace that for the heck of it tomorrow.

 

tps usually causes fluctuations in idle speed, IAC motor (valve) is what controls idle speed when the butterfly valve is closed so that owuld be my best guess however you seem to have already replaced this

at idle (cold, open loop) the PCM monitors the following
Battery voltage
• Crankshaft position sensor
• Engine coolant temperature sensor
• Intake manifold air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distribu-
tor)
• Park/neutral switch (gear indicator signal—auto.
trans. only)
• Air conditioning select signal (if equipped)
• Air conditioning request signal (if equipped)
Based on these inputs the following occurs:
• Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
the injection sequence and injector pulse width by
turning the ground circuit to each individual injector
on and off.
• The PCM adjusts engine idle speed through the
idle air control (IAC) motor and adjusts ignition tim-
ing.
• The PCM operates the A/C compressor clutch
through the clutch relay. This is done if A/C has been
selected by the vehicle operator and requested by the
A/C thermostat.
• When engine has reached operating tempera-
ture, the PCM will begin monitoring O2S sensor
input. The system will then leave the warm-up mode
and go into closed loop operation.


at idle (warm, closed loop) the PCM monitors
:
• Air conditioning select signal (if equipped)
• Air conditioning request signal (if equipped)
• Battery voltage
• Crankshaft position sensor
• Engine coolant temperature sensor
• Intake manifold air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distribu-
tor)
• Battery voltage
• Park/neutral switch (gear indicator signal—auto.
trans. only)
• Oxygen sensors
Based on these inputs, the following occurs:
• Voltage is applied to the fuel injectors with the
ASD relay via the PCM. The PCM will then control
injection sequence and injector pulse width by turn-
ing the ground circuit to each individual injector on
and off.
• The PCM monitors the O2S sensor input and
adjusts air-fuel ratio by varying injector pulse width.
It also adjusts engine idle speed through the idle air
control (IAC) motor.
• The PCM adjusts ignition timing by increasing
and decreasing spark advance.
• The PCM operates the A/C compressor clutch
through the clutch relay. This happens if A/C has
been selected by the vehicle operator and requested
by the A/C thermostat.


more information can be found on page 288 of the 2002 FSM if you would like to do some more indepth reading

 

I just replaced the exhaust, it was totally rotted out. I bet that was causing a bit of a issue with the 02 sensor leaning it out.

Here is what I noticed on the TV cable. The TV cable arm on the tranny seems to be really sticky and not returning on its own. I have not given it much of a look yet because I am eating lunch, but after lunch I will jack it up further and watch it when my friend moves the throttle. I bet that isnt returning all the way after heavy throttle. That would totally cause the issue I am having with the transmission not shifting after I use heavy throttle.