5.9L engine idle problem
 

Hello everyone,
So here's my problem, i'm taking my truck to a mechanic in afew days to try and get this fixed but from searches on the internet i've found alot of people with this happening and in every case it seems they've done something different to fix it or couldn't get it fixed and alot of them complained about the end cost after a mechanic went through and replaced part after part.....so here's the problem, i bought my 99 ram 1500 5.9L 4X4 recently and drove it home with no problems (200miles) a day or two later i had it running at idle and all of a sudden my idle drops to about 5 or 600rpm and it sounds really rough like it struggling to stay running.....i reved it up once or twice and it went back to normal idle...around 900rpm i think, so i didn't think much of it.....well later on i was driving and came to a stop and while sitting there idling it suddenly dropped down to the 5-600rpm ranged and was idling rough, engine shaking ect and the light turned green...now i went to take off and the engine was stuttering and cutting out and i started to slow back down to almost a standstill, at the same time i heard popping or backfiring into the air cleaner i believe...i stepped on the peddle to the floor and it cut out for a second then the engine roared to life and i got upto speed (35mph)....now the CEL has come on and i've read the codes and it says its running rich and the O2 sensors are bad, we cleared teh code and i continued driving it....it still does it completely randomly and usually does cause the CEL to come on again.......now i went through and replaced plugs, wires, cap, and rotor....exhaust seems to have good pressure comming out the pipe but it still seems to do this...its completely random....does it when its warmed up or when its cold.....might do it once in 40 miles of driving or several times...there's no pattern........i should also mention it seems like its getting really poor mpg....i havn't done the math to see exactly what my mpg is but i can put half a tank in it and drive it alittle around town and go home and i'm almost back on E again.......... dont know if this is part of the problem but i've noticed that to hit hiway speeds (70mph) i seems like i gotta have the peddle to the floor........anyway, i just want some idea of what it might be so that i can point the mechanic in the right direction without costing me an arm and a leg in parts tryin to fix this......mechanic looked at it once and because it didn't throw a code and when he test drove it afew miles it didn't do it he thought it was fixed........PLZ HELP!....ty.

welcome to df.
post your truck year, engine, etc in your signature so its easier for us half blind old people to find it.

post your actual CEL codes, don't translate them.
have you replaced your front O2 sensor yet ?

I have almost the exact problem on my 2000 ram 5.9 ext. cab w/ 104,000 miles on it and I have changed cap, rotor, plugs, wires, iac and tps sensor, coil, theromstat(not related to problem), one of the two o2 sensors(sensor 2) and none of these have fixed it. My next approach is checking the fuel pressure, changing the temp sensor or injectors but other than that not sure but will keep tryin. hope this helps and or if ur mechanic fixs the problem please post solution, thanks and good luck.

1999 Dodge Ram 1500 Laramie 4X4 ext cab 5.9L

still tryin to figure out how to put it in my signature.
also....dont know if this has anything to do with it but i do hear a very very slight and quiet sucking sound when it idles rough...and i noticed for the 1st time yesterday that it will randomly rev upto about 2grand rpm when idling....did it once in about 15 minutes....aside from that occasionally i'll barely touch the peddle and it will go upto about 2000rpm and seems like it sticks there for a second before it comes back down....now it doesn't always do this and i'm just mentioning it incase its connected to the problem.

Check your TPS.

Change the pre cat O2 sensor.

+1 for oxygen sensor 1 (pre-cat). The second sensor does nothing for the running of the engine, just tells you when the catalytic converter needs replaced. The first sensor helps the PCM determine the air/fuel ratio, so its very important. This would explain the lack of power/sputtering AND poor MPGs. What was the exact code?

Just to recap:

You said you had codes saying that the engine was running rich, and that ~both~ O2 sensors were unhappy. It sure would be nice if problems could be fixed by clearing the codes. It would be helpful if the posted any codes you're getting now, especially the O2 sensor codes. If the engine really has been running rich, it's possible that the cat is now screwed up. You might just save yourself a lot of trouble in the long run by taking it off and having a look-see inside it, especially if you're getting a code that says it's bad. Got a lift, a torch, and a half hour to spare?

Another thing: The randomness and popping back/misfiring clues just made me think of the crankshaft position sensor (CKPS), not to be confused with the camshaft position sensor (CPS) in the distributor. I have read accounts on here of how a bad one can cause misfiring, and I'm guessing a ~really~ bad one can be very hard on your starter. I've been having a random stallling/stumbling/misfiring problem with my 94 318 and my next attempt is going to be the CKPS.

The random high idle w/slow return sounds like a separate problem: as sticking IAC. The low/sucking idle, though, sounds like the pre-cat oxygen sensor.

I hope you get it fixed without any misadventures along the way.

thx guys....going to my mechanic today with these suggestions....dont know if it matter but my CEL went off this morning and hasn't been back on...should still show a code when we check it tho.

It's just that the truck knows it's going to a mechanic. :D

Was there ever a solution found for this. I have an 01 5.9 magnum and it's doing almost the exact same thing. It randomly cuts out and while it's doing that you can hear a small backfire through the throttle body. Let me know. Thanks.

There probably was, since it was four years ago.

In what ways are your symptoms different ("almost the exact same thing") and what have you done to try to correct it?

I knew it was almost 4 years old. That's the main reason I asked here. I guess the symptoms are the same except the lack of power wile it's not cutting out. As of now it has new plugs, wires, cap and rotor, and fuel pump assembly.

That makes it easy, since the OP's symptom picture included diagnostic codes indicating failed oxygen sensor(s). By the time the PCM sets that code your sensor has been failed for a long, long time. Even without the codes the OP's symptoms point at the O2 sensor.

His inability to discern a pattern doesn't really mean that there wasn't one. The pattern is very predictably this: Any time the exhaust stream is running (relatively) cool the engine runs like crap, and any time the exhaust stream is running relatively hot it runs much better. Higher RPM or higher load will heat the exhaust, idle or cruising at highway speed will cool it. The root of it is that these sensors have a certain minimum operating temperature below which they are inaccurate, and as they age that minimum temperature increases, eventually to the point at which this symptom picture appears.

The loss of power comes about due to the fact that the typical failure mode of an oxygen sensor is a false rich reading, which causes the PCM to run the engine too lean. Which is also what causes the low and usually lumpy idle, usually with a sucking sound in the intake while the idle is low -- the sucking sound is coming from the IAC being wide open as the PCM tries to get the idle speed up to target.

Something else to consider is that oil fouling/carbon build-up on the sensor will present in much the same way because the sensor, being coated, sees a lot less of the exhaust stream and will again deliver a false rich reading. So check out the plenum gasket while you're at it. If it's found to be compromised, you'll want to fix it right away and also test the catalytic converter for clogging. With luck, if this is what's going on, you'll catch it before the converter failure causes a cracked cylinder head.

Well the truck doesn't have a converter anymore. It actually has long tube headers with pipes that Y together just before a magnaflo muffler. It also has no rear oxygen sensor.

We'll start by cleaning the 02 sensor and see if that changes anything.

The MAP Sensor can also do this. First thing to do is is clean your throttle body really good. If the air bypass port for the IAC has a lot of carbon in it, it will cause idle problems.

If it ran fine like that in the past, then it's likely the sensor gone kaput. Try unplugging it to force the PCM to stay in open loop, and take a drive. You'll get a check engine light and codes due to the unplugged sensor. If the symptoms don't appear with the O2 sensor uplugged, it's time for a new sensor.

It was suggested above that you might try cleaning the thing, and it might sometimes work for a while, but it's much better to replace the sensor if it's failing. The risk is that most folks would be happy to call it a win if the symptoms mostly disappear, but if the engine is still running lean it'll accelerate the wear of the expensive parts in the combustion chambers. It'd actually be better, if the part has failed, to just leave it unplugged until you can get another installed. Running a tad rich, with no catalytic converter to be harmed by it, isn't really a problem.

I have extensivly cleaned the TB. I took it off and cleaned all through it and put a new base gasket under it. We'll unplug the 02 sensor and see where that gets us. I hadn't even thought about the MAP sensor. Where is it located exactly? I can't remember seeing one on the side of the intake anywhere.

It's hanging on the front of the throttle body. I'll be surprised if it's at fault. Not "woulda bet my house on it" surprised, but still surprised. It's one of those parts that gets replaced by guess and by golly fairly often, to no benefit except that of the parts store.

The little rubber elbow that feeds can be problematic though, but, that's pretty rare.

[QUOTE=UnregisteredUser;3219502]It's hanging on the front of the throttle body. I'll be surprised if it's at fault. Not "woulda bet my house on it" surprised, but still surprised. It's one of those parts that gets replaced by guess and by golly fairly often, to no benefit except that of the parts store.[/QUOTE

Ok. Haha, guess that's why I didn't see it on the intake. We'll start by unplugging the 02 sensor and see what happens. I'll post back with the results.

Ok.... We unplugged the 02 sensor and the truck isn't cutting out anymore. We're getting a new one to put on and see where we're at.

That sounds like an erratic Idle air controller,or IAC. Check and make sure it's not loose on throttle body.

There ya go. As has been said several thousand times, go with a dealer part if you can, and if not prefer Denso, then NTK, but stay away from Bosch. (The Bosch parts aren't bad, per se, but our PCM's don't like them.) You're going to see a world of difference with the new one in there. More power, better mileage, and an end to the painful burn and itch of hemorrhoidal tissue. Or at least one less pain in your ass.

Thanks. You've been a huge help and it's much appreciated. If we have anymore trouble I'll post back.

It's nice to see people follow through with their post. It frustrating to read 3 or 4 pages to see there was nothing posted saying what fixed their problem. This is the first in five post I have read that did. I have an 02 1500 4x4 with a 5.9 and automatic . I know 02 is a 3rd Gen but I would think 2nd Gen people would know more about the 5.9. In the last two days my truck has misfired 3 times and it seems to have a random but constant hesitation. It's does it during acceleration and cruising speeds in most gears. Have not driven it in first to see. But second, drive and overdrive. It seems to idle smooth and no noticeable lack of power. The rpms don't seem to fluctuate. There is no check engine light on. I'm just looking for some advise. I have not changed plugs or wires. I was trying to see if it could be bad gas or other options there are. I would think with the misfires my check engine light would come on. I live an hour and a half from an auto zone or checkers. So if I need to read the codes I'll have to take it to the mechanics. I have done the key trick and it flashes ------ then done. Thanks

Have you checked your plenum? When is the last time plugs/wires/etc were changed? How does it run when you stick your foot into it? (hard acceleration)

You basically listed my situation with my 98 durango 4x4 with the same engine. I have read a ton of posts and have replaced/reset/tuned up, etc.
iac, tps, map, cap, rotor, wires, plugs, clean TB, scanned o2 sensors, battery,
taken it to mechanics. It is totally baffling that nothing seems to make this problem go away. It gets better when I reset the computer. It slowly returns to irratic idle and dieing at stop signs. I have owned this truck since 1998 and it ran great until the crank sensor failed. After replacing that, it ran fine for a few months and then this un fixable idle problem showed up. I answer you in hopes that if you ever crack this mytery, I will maybe hear through you or a response to this thread.

What brand crank sensor? If it's an aftermarket piece, replace it with genuine mopar sensor. I bet your problem goes away.

I have actually wondered about the sensors on the TB. I did have to replace 2 defective tps sensors. Both new out of the box. The crank sensor is just a rotation counter over time. It is either working or not. The others on the TB are variable and more sensitive to being made to a higher specification. I think that has more validity. Like I said before, so much speculation but no real definable solution. I think there is hage number of variables that create the same symptom of erratic idle, that it is just a pain to fix.

That's what I thought about the crank sensor as well, however, another member was doing some testing with an O-scope..... and he noticed the several cylinders had consistently weak spark. He replaced the crank sensor, and the problem was gone. I have also seen MANY instances of the 'mystery miss' caused by aftermarket crank sensors. So, while *theoretically*, it either 'works' or it 'doesn't', it seems in actual practice, that is simply not the case.

I can appreciate what you are saying. I will look into the mechanics. I would have to be convinced that there is a technical need for the the crank sensor to do more than synchronizing spark clock. It has always been my understanding that the intensity of the spark is not affected by the crank sensor. If the sensor is out of alignment or damaged, I could see the potential for an intermittent clock signal or a week exciter on the flywheel, causing one plug to not fire. The one thing that will set off the engine light is a misfire of a plug. This is one of those things that will probably surprise me. I actually scoffed at a post that told me to check my transmission fluid for bubbles or froth. At one point, The engine acted like it was missing and the vehicle would feel like it was driving through large puddles of water at high speed. It turns out that if the fluid is not at the proper level or has bubbles/froth, the fluctuating fluid pressure and torque would confuse the computers management of the transmission. I topped it off and that particular problem went away immediately.

And that is the exact same reasoning I used when chatting with the other guy. :) I am in complete agreement with you, that is how it *should* work. However, there is a fair bit of evidence to the contrary. These trucks simply do NOT like aftermarket sensors in critical locations.

On that, there is no argument! I can be absolutely wrong and happy. I am sick to death of this problem. I spent a week chasing rabbits on the bad TPS. (Only to find out the new one was bad too.)
One tends to get tunnel vision and start doing the same things over and over looking for a different outcome.
right now, if someone told me to use chromed Schrader valves on my left rear tire if I want my idle problem to go away, I would try it!

Ya just never know.... that might work. :D