Idle issues. 03 1500 5.7

[Micah201]

Hi there. I'm new to the site and am having an issue with my truck. Just some background info. It's an 03 ram 1500 with a 5.7 hemi. Truck has aprox 345,000 miles. All original, nothing ever done to it performance wise. About 4 months ago I started having an issue with the idle. When I shift to park or neutral the idle is all over the place. Revs up and down. Varies by about 1000 rpm at times. If I leave it be it will eventually die. Cranks right back up though. If I shift the truck into reverse or drive the idle smooths out, although it does seem to idle low. It will hold a steady 600 rpm. When accelerating, it's not smooth at first. Seems that the first 10% of the pedal does nothing. After that it's smooth sailing. The only dtc's are for the oxygen sensors. Cat "fell" off years ago, and the codes have been there since without causing issues. About two months ago I pulled the throttle body and intake manifold. Cleaned them both very thoroughly. Put it back together and had no issues for about another month. Idled perfectly, throttle response was smooth and instant. About a month after I cleaned everything out it started acting up again. Same issue. I pulled it all apart again and cleaned it out, but this time it made no difference. I'm leaning towards replacing either the throttle body or the throttle position sensor. Just not sure which one is causing the issue. By throttle position sensor, I'm referring to the part that the throttle cable connects to, which transfers the throttle imput electronically to the throttle body. (Not sure if that is the correct name for that part). Just looking for some ideas on how to narrow the problem down. I've turned many a wrench, but I specialize in diesel, gas engines are just foreign to me. I appreciate any help you can offer. Thanks, Mike

I know sometimes it helps to see the problem so I uploaded a video of what it's doing. Here is the link. https://www.youtube.com/watch?v=5AhbBYwdg1w

 

[Hemi8073]

I would start by checking for a vacuum leak anywhere like on the top or bottom of the intake manifold, then replace the factory primary O2 sensor. It's the one before the cat. Then pull throttle body, clean it, reinstall and make sure all the connectors are plugged all the way in on the throttle body and map sensor. Hope this helps you out brotha

 

[Hemi8073]

If you replace the O2 sensor only go with mopar. I have had a few from parts stores and they were garbage. Had a lot of surging and stalling and once I put the authentic mopar 02 in all of that stopped and has idled perfect ever since

 

[Micah201]

I did check for vacuum leaks. None that I can find. I have pulled the tb and cleaned it again. I also tried the reset procedure I found on this site. Which did work for about two days. Idled like a dream. Then went right back to the same problem. I haven't bothered with the O2 sensors. Being that the cat is gone, I would think it would just throw the code again wouldn't it? Like I said before I'm not familiar with these engines (or any gas engine for that matter) and their control systems. So I'll try anything by this point.

 

[RonJon '06]

If resetting it made it idle better then I would be thinking the fly by wire as well, either the TB or the accelerator pedal position sensor (APPS). I don't know if that explains why it idles better in gear though. If the transmission fluid is low it can cause it to idle funny. Also, I think the '03 guys have done a mod to boost the transmission line pressure. That might not be it but I usually like to rule everything out before I start throwing parts at it.

 

[Micah201]

I was just reading on here about the atf level. Never considered the transmission playing a part in it. Had the trans rebuilt about a year ago. I checked the fluid level, it was just a touch low. Topped it off and took it for a drive. Ran it long enough to get it up to temp, didn't seem to make a difference though. Think I should try to reset it now that it's topped off? I know resetting it will work, but so far it's only been a temporary fix. Thank you for telling me the name of that part. (apps) I'm assuming it's just a potentiometer that relays throttle input to either the tb or pcm? If so I can test that part if I know what values to look for. Will have to do some more research on that. Helps now that I know what it's called. On a side note, any idea where I can find more info on boosting the line pressure. I've never liked the way this trans shifts. I tried searching it, but no luck.

Thanks for the help everyone. Really appreciate it.

 

[Micah201]

I was able to find the line pressure mod. Will definitely be doing that soon. Still looking for values on the apps. Thanks again for all your help.

 

[RonJon '06]

Here's the TMR thread. I'm not sure what values the APPS sends to the PCM but I believe there are two sensors and I would think that the signal would be constant if its just sitting at idle. You're video looks like it might be swinging up and down quite a bit.

http://www.ramforum.com/f76/03_tmr_delete_mod-3510/

 

[Micah201]

Thanks. That's actually a different mod than the one I came across. Both seem beneficial. Guess I need more research, lol. I have my apps and my fluke on the table as I'm typing this. Going to see what I can figure out with it. Watching the throttle body while it's trying to idle I can see the butterfly plate going crazy. It seems as though it's trying to compensate for some type of erratic input. My only concern is that it seems as though any erratic input from the apps would still not be able to cause it to drop below normal idle. That should be controlled from the pcm or tb itself. (From my understanding anyway)

 

[Micah201]

Ok so I was able to find a diagram for the apps. Tested it and found a steady increase and decrease in ohms. So the apps is not the problem. Cant find any info on how to test the tb and internal throttle position sensor. As much as I'd like to point the finger at the tb. I'm still not convinced that it is the problem. (due to the idle smoothing out while in gear.) So I double checked the trans fluid level, added a little more and preformed the reset procedure again. While I was under the hood I went ahead and did the tmr delete. About to make a 60 mile round trip to pick the wife up from work. Will see how it does and let you know.
Thanks again for all the help, Mike

 

[RonJon '06]

Sorry, I had found the line boost thread and, since you're an '03, the TMR thread but just before I posted I saw that you had found the one on the line boost.

Anyway, Ive never done it before but maybe you can check for a steady signal going from the PCM to the TB? Also, here is a thread for adding an additional ground wire to the TB that is supposed to smooth out the idle.

http://www.ramforum.com/f44/grounding_tb-12879/index4.html

 

[Micah201]

I'm always up for free mods. And more points to ground can never hurt. Seeing that the intake manifold is plastic, I suppose it relies on the pcm for its ground. Which would seem like a very resistive / noisy source. It's easy and it's free. I have everything I need right here in the shop. So I'll likely do it at work tomorrow. I did the tmr delete just because I was already under the hood and it only took two seconds to locate and cut the wire. And it did make a noticeable difference. Especially under hard acceleration. Might be my imagination, But it seemed to effect the 2nd-3rd shift as well, not really sure though. I will be looking into boosting the line pressure very soon. I've been wanting to do that for a long time. (since the rebuild) And now that I know what I need, I will be looking into that this weekend. I have a pretty good source for resistors and other parts of that nature. So it should cost next to nothing. As for the current issue. I took the long way there and home. About 85 miles total. With 5 or 6 stops along the way turning it off and restarting to give it a chance to register that there is a problem. It gave me no issues whatsoever, but fingers are still crossed. It also acted fine for a few days the last time I did the reset. I guess time will tell.

One other thing I have noticed is that in most of the threads I have read about people having issues with the throttle body it seems like they usually have the lightning bolt icon on the gauge cluster either lighting up or flashing. That icon has never even blinked on my truck except when turning the key on before starting. Could that mean anything?

 

[Redtruck-VA]

Welcome, obviously you've done more than a few things right to have over 300k miles on the old girl. Well done. Normal warmed up idle is 525rpm, cold startup will be higher. I would freshen all the ground connections and check the wires closely for corrosion. If the battery is more than 5 years old I would replace it regardless if it test good or not. Are you cleaning the TB with brake cleaner. Don't use carb cleaner it contaminates the electronics. There are two O2s, one forward of the Cat and one aft. With the cat removed you should have a code for the rear O2s. If you are getting any codes on the front O2s then that is a different situation and needs to be addressed. The front O2s is what feed AFR to the PCM telling it how to fuel. Trans level is critical for idling and spark plugs gapped to .044. Use only the original Champion Copper or NGK 5306. TMR and trans Line Booster are both good mods. And being a 03 I'd do a compression check looking for the odd cylinder and then check for a broken valve spring. With your high mileage I wouldn't suspect a valve spring, but it is a 03 and any idling problem points in that direction. Good luck..

 

[Hemi8073]

I don't have cats either and it still made all the world of difference. I am cammed and use to stall every now and then and surge at times, I have since went to a little bigger cam and with the new 02 I have yet to even come close to stalling. But like said only use mopar 02's from the dealership. And to red trucks point about spark plugs, I have heard people say that only go with stock heat range copper but I went with the expensive iridium champions and have never had any issues what so ever and truck runs amazing. That's just from my experience.

 

[Redtruck-VA]

I've done some testing and have found that using the stock range plug Champion or NGK you won't have any problems. But if testing proves something better works by all means go with what works best for your truck. I actually use NGK 4306 gapped at .040. I also have 6.1 coils wired in a custom wiring loom.

 

[Micah201]

Thank you all for the great input. And thank you redtruck for the welcome. I like to think I've taken care of the truck, but it's seen better days. I've always stayed on top of the maintenance. Fluids changed at regular intervals. (mobile 5w-30 conventional since day one). And I've always done my best to fix the small things before they become bigger things. It's reliably taken me to 48 of the 50 states many times. And once I replace the front u-joint I'd trust it to still do it again with no worries. It's beginning to show it's age but it's been a darn good truck.

The idle once it's warmed up hovers between 5 and 6 hundred rpms. So the 525 you stated seems accurate. Just seems low. It's always done that though. Usually when it does drop that low I've found that if I gently tap the go pedal, (gas pedal) (that's my diesel roots kicking in) it will rise to about 650-700 rpm and stay there. The idle is noticeably smoother at 6-7 hundred rpm, versus 5-6 hundred.

All of the ground connections I can locate are clean and tight. No corrosion to be found. Besides the rust on the body, but that's another issue entirely. Connections are clean and corrosion free.

Battery is about 1 1/2 years old. Optima red top.

Plugs were replaced about 20k miles ago. Don't remember the specs on them although I do remember them being ngk. Gapped to factory specs as always.

I did use brake cleaner to clean the tb. I use brake cleaner for pretty much any cleaning under the hood. Cleans great, and evaporates super fast. (side note: not to be used on a hot engine... don't ask me how I know. My wife probably still has nightmares, lol. I knew better.)

The only dtc present is for the rear 02s.(post cat) Would love to block it off once and for all to get rid of the light. But that's another project for another time.

I've read quite a bit on here about the valve spring issues on the 03 year model. I had planned to preform a compression test after work today, but my compression test kit seems to have grown legs and wandered off since the last time I used it.
I have my doubts that a broken or collapsed spring is playing a part here though, seeing as when I clean and reset the tb the problem goes away, even if it is only for a few days. I can't see a clean and reset even temporarily fixing a problem such as that. But I'd still be curious to know what values a compression test would return on such a high mileage engine.

Left the cummins at home and took the old girl to work today. I drove the truck quite a bit. Made a point to use it instead of the company truck for all the parts, and supply runs. It ran great, Idled perfectly, great throttle response. I'm hoping that maybe it was something as simple as the trans fluid being low. Keeping my fingers crossed for now though. Thanks again for all the input and advice.

Also Hemi8073, I will be looking into the mopar 02s for the pre cat sensor. I figure it can't hurt. What's the stealership requiring for one of those these days? I prefer to keep both my arms and legs.

 

[Redtruck-VA]

You can use two non-fouler stacked. Drill out one and screw it onto the sensor, weld up or block the other non-fouler and screw it into the pipe. With them all screwed together the O2s is isolated and won't throw a code. You can also wrap the O2s up with aluminum foil and hose clamp it out of the way. The way it works is the front and rear O2s count voltage shifts (flips) if they have the same count you get a code. By isolating the rear O2s it's count is low and no code.

 

[Micah201]

RonJon '06. I wanted to give you an update on grounding the throttle body. I admit I was skeptical that it would make any difference. But like I said last night, more points of return to ground can't hurt.

I started out by doing some testing. I was able to track down a diagram of the wiring for the tb. There are two separate grounds. One for the internal throttle position sensor. And one for the throttle control. It's dificult to get a true reading on the tps ground as its routed through other electronics. (always reads high resistance in the 2k-3k ohm range) This is the ground for the +5 volt reference voltage read by the pcm. The throttle control ground on the other hand is a direct ground. Passed directly through the pcm to the chassis.

This is where things got interesting. With the battery disconnected and a good connection to the throttle control ground at the tb, and where the pcm ground connects. I got a reading of 0.4 ohms. No biggie. Great connection. (started to doubt the extra ground making any improvements) I reconnected the battery, skipped the reset procedure for the tb and started the engine. Got my test leads in place and made sure I had a good connection. To both the throttle control ground at the tb and the pcm ground. My reading was all over the place. Ranged anywhere from 1-90 ohms. I never actually saw the 90 ohm reading, but my fluke recorded it.

So assuming I did my testing correctly. I think I did, (although I'm no electronics wiz. so I may have done this completely wrong) But if I did it correctly. That would mean that there is a great deal of varying resistance, or noise, or interference. (however you want to word it) across the pcm's ground bus.

To check if an added tb ground made any difference. I used a test lead with an alligator clip on each end. I connected one end to a chassis ground on the opposite side of the vehicle as the pcm's ground. And clipped the other end to one of the tb mounting bolts. I repeated the previous tests and read zero ohms in both scenarios. With the battery disconnected, and with it connected and the engine running.

I decided that since it was such a seemingly drastic difference. I left the test lead in place and took it for a test drive. I have to say, I did notice a significant difference in both the idle and throttle response. It idled smooth as butter. And it seemed as though I didn't need to give it nearly as much throttle to get it moving as I did before the test lead was in place. Just to make sure it wasn't simply a placebo effect. I pulled over turned the truck off disconnected the test lead. And took it around the block again. The idle had its normal variation again, and it felt sluggish again. Stopped again. Reconnected the test lead, and around the block I went again. Idle smoothed out again, and the sluggishness was gone.

Now before anyone attacks my methods of testing. I've already stated that I am by no means an electronics wiz. I do have a basic understanding of them though, and I know just enough to get myself in, and usually out of trouble. I may have done all my testing incorrectly. But one thing I do know is that a simple ground connection did in fact make a noticeable difference. Needless to say I'll be making a permanent grounding solution for this issue tomorrow.

 

[Micah201]

Redtruck, I didn't realize it was that easy to fool the sensor into allowing the cel to turn off otherwise I'd have done it long ago. The non-fouler you mentioned. Where can I find a couple of those? Or using the foil and clamping it up and out of the way. What are the chances of finding a bolt with matching threads to plug the hole in the pipe? I'd think using the non-fouler combo, or a simple bolt would both accomplish the same goal. As long as the hole is plugged I should have no worries, correct?

 

[Redtruck-VA]

Redtruck, I didn't realize it was that easy to fool the sensor into allowing the cel to turn off otherwise I'd have done it long ago. The non-fouler you mentioned. Where can I find a couple of those? Or using the foil and clamping it up and out of the way. What are the chances of finding a bolt with matching threads to plug the hole in the pipe? I'd think using the non-fouler combo, or a simple bolt would both accomplish the same goal. As long as the hole is plugged I should have no worries, correct?

Your local auto parts store will have a plug. I've used the O2s **** and plug for a oil drain on the differential cover. I think even some spark plugs will fit the ****. They will also have the non-foulers.

The external grounding works better on some truck over others. Most likely depending on the individual trucks grounding. The PCM uses both a clean (filtered) ground and a chassis ground. I have a external ground wire that runs from the PCM to the TB to a valve cover bolt and finally to the fender by the battery.