Rough idle on 5.7 Hemi

FancyStancy · Oct 21, 2013

Hello,
I have been struggling with an issue that seems to be pretty common for the 5.7 Hemi. When starting the truck, it starts by dropping rpms, and then rising, and then dropping again. It almost sounds like it has some kind of race cam, lol. The idle might smooth out for a minute or too but then gets really rough again. When I accelerate, no matter if I just started the truck or if I have been driving for a while and am leaving a stop light, the truck studders, and then will accelerate dramatically. I have also had a few times where when turning the truck at low speeds, it had died. I have heard lots of guys talking about cleaning the throttle body which I have done real good. Any other opinions?
Thanks

truckin151 · Oct 21, 2013

Make sure all the gaskets are installed right around the tb, when was the last time the plugs were changed? Ran any seafoam through the brake booster? If so check the hoses for vac leaks.

FancyStancy · Oct 21, 2013

Thanks for the response. Everything around the throttle body is installed correctly. I never removed the tb, I just cleaned it by opening the valve and using tb cleaner. Not sure when the plugs were changed. I bought the truck at 68k and it is now at 72k. And never been sea foamed.

HLram · Oct 21, 2013

Take the TB off to clean it. It is really easy to do so and that way you won't get all the crap from the TB that you cleaned off into the intake. Also research on here to make sure you get the right cleaner so it doesn't affect the electronics. The intake itself may have a boatload of gunk built up inside it as well. Also the plugs probably do need to be changed. 30,000 ish miles is when they are supposed to be changed I believe. My 07 has a little bit of a rough idle even when it is cleaned and has new plugs in it. It has 160,000 miles but has always stumbled ever so slightly. My 12 model, however, is noticeably rougher. Has been since the day it was bought. It hasn't really gotten any worse. Got a little smoother the one time I tried Royal Purple oil. Went right back to Amsoil after that one time. I grounded the TBs on both of mine to see if that would help, with zero success on either one. I don't know, maybe a PCV valve needing replacement or something on yours? I am curious about this seafoam in the brake booster hose thing that was mentioned earlier. I wonder what that does? Welcome BTW. And good luck with your issues.

truckin151 · Oct 21, 2013

Yes absolutely remove the tb to clean it

FancyStancy · Oct 21, 2013

HLram said:
Take the TB off to clean it. It is really easy to do so and that way you won't get all the crap from the TB that you cleaned off into the intake. Also research on here to make sure you get the right cleaner so it doesn't affect the electronics. The intake itself may have a boatload of gunk built up inside it as well. Also the plugs probably do need to be changed. 30,000 ish miles is when they are supposed to be changed I believe. My 07 has a little bit of a rough idle even when it is cleaned and has new plugs in it. It has 160,000 miles but has always stumbled ever so slightly. My 12 model, however, is noticeably rougher. Has been since the day it was bought. It hasn't really gotten any worse. Got a little smoother the one time I tried Royal Purple oil. Went right back to Amsoil after that one time. I grounded the TBs on both of mine to see if that would help, with zero success on either one. I don't know, maybe a PCV valve needing replacement or something on yours? I am curious about this seafoam in the brake booster hose thing that was mentioned earlier. I wonder what that does? Welcome BTW. And good luck with your issues.

Thanks for your info. I will completely remove the throttle body and give it a good clean. My intake is a K&N so it is very simple to remove and I have cleaned it good. Also my filter is fairly new and clean. Do you think that any of this would have to do with the idle air control valve? I am only thinking this because the truck stalled while turning. And by plugs do you mean spark plugs? sorry, im still learning. Thanks

truckin151 · Oct 21, 2013

Take out the iac and make sure it's not gummed up. Plugs = spark plugs, just go with the copper champions nothing special hemi's don't like the others specially when stock. Swap out all 16 of them.

FancyStancy · Oct 22, 2013

Okay, thank you for clarifying. I will also check on the IAC valve. I also just ran very simple diagnostics from my Bullydog GT Tuner. Here are the codes I got back:
PO171 System Too Lean
PO172 System too rich
PO174 System too lean
PO456 Evaporative Emmission system leak detected(very small leak)
PO2099 Post catalyst fuel trim, system too rich
Do any of these codes have to do with stuttering, surging and rough idle? I ran these codes about a half hour ago. About a month ago I ran for codes and I got all the same codes but had 1 more saying I had a cylinder misfire. For some reason it went away. Wouldn't that have to do with spark plugs? Thanks

truckin151 · Oct 22, 2013

Well that makes a bit of a difference.

Still do all the above and.. Replace the O2 sensors, up and down stream of the catalytic converters. That should solve the to rich to lean or you will get a bad catalyst error code. The small evap leak could either be the gas cap going bad, the hose to the gas cap has a leak or the egr valve has a leak.

Easiest way to check some codes, pull the battery cable, install new O2s and a new gas cap, reattach the battery cable start the truck and let it run and see what code(s) pop back up. A bad cat or bad o2 would definitely cause a surge.

FancyStancy · Oct 22, 2013

truckin151 said:
Well that makes a bit of a difference.

Still do all the above and.. Replace the O2 sensors, up and down stream of the catalytic converters. That should solve the to rich to lean or you will get a bad catalyst error code. The small evap leak could either be the gas cap going bad, the hose to the gas cap has a leak or the egr valve has a leak.

Easiest way to check some codes, pull the battery cable, install new O2s and a new gas cap, reattach the battery cable start the truck and let it run and see what code(s) pop back up. A bad cat or bad o2 would definitely cause a surge.

Really? I didn't know a bad cat or bad 02 sensor could lead to the surging. This now makes a lot more sense now. I have electronic exhaust, meaning with the press of a button I can switch from a dump directly out of the headers or close the dumps and run a full, legal, exhaust system with dual cats running to 1 muffler and single exit pipe. When i have the valve open(straight piped) the truck runs a lot smoother. The idle is very smooth and sounds good. The truck still stutters a little when accelerating. But when I have the valves closed(running through cats and muffler) that is when i have my problem. The truck starts to lope and sound bad. It even stutters more when accelerating. Could I just have a bad cat? 02 sensor? Even when the valves are open, some exhaust still runs through the cats which could be causing it to stutter on acceleration? Thank you so much for sharing your knowledge, lol. You know a lot and you are saving me a lot of money! That is key when you are a kid haha.

KGBIGCOUNTRY · Oct 22, 2013

STOP USING TB CLEANER!!!! You will damage the sensor in the motor. Use Non-Clor Brake cleaner. Ryan has you going the right way on this because of your codes. You can also pull the plugs and check them, if it was me I would replace them.

truckin151 · Oct 22, 2013

FancyStancy said:
Really? I didn't know a bad cat or bad 02 sensor could lead to the surging. This now makes a lot more sense now. I have electronic exhaust, meaning with the press of a button I can switch from a dump directly out of the headers or close the dumps and run a full, legal, exhaust system with dual cats running to 1 muffler and single exit pipe. When i have the valve open(straight piped) the truck runs a lot smoother. The idle is very smooth and sounds good. The truck still stutters a little when accelerating. But when I have the valves closed(running through cats and muffler) that is when i have my problem. The truck starts to lope and sound bad. It even stutters more when accelerating. Could I just have a bad cat? 02 sensor? Even when the valves are open, some exhaust still runs through the cats which could be causing it to stutter on acceleration? Thank you so much for sharing your knowledge, lol. You know a lot and you are saving me a lot of money! That is key when you are a kid haha.

So if I understand your setup correctly, it goes header > Cutouts > Cats > Muffler.....This correct?

Are the Cutouts installed infront of or behind the front O2 sensors?
How often are the cutouts open vs closed?
Do you have any sort of tune to turn things off? Basically if you by pass the cats, without a tune to get rid of the cats, you will get those codes regardless of if the O2's are working or not. Really need more info on your truck now, as well as what you have and have not done to it instead of adding individual pieces of information here and there.

KGBIGCOUNTRY · Oct 22, 2013

With him having a GT tuner we can rule out a CMR tune. I agree a full info on the truck or even pics of the setup since the op is lifted will give us insight.

FancyStancy · Oct 22, 2013

Yes, you have the setup correct. I am not sure of the position of the 02 sensors. The cutouts are usually open, but in the pictures they are closed. And no, my computer has no tunes. Even though I have a bullydog, it is stictly a monitor with minor adjustments like shift points and what not. That is why when I got those codes I didnt take them too seriously.And there is not much more done to the truck that would affect anything. I do have aftermarket headers that came on the truck when I bought it. It is hard for me to get to detailed because of my little knowledge of the trucks past. Here are some pictures of my exhaust setup:

FancyStancy · Oct 22, 2013

Here are two more shots of the two cats that run from both dumps to my muffler and then out the single exhaust. If anyone knows what brand muffler that is please let me know. It doesnt look very expensive, kinda looks just thrown on there.

KGBIGCOUNTRY · Oct 23, 2013

Cant tell 100% because of the photo but looks like the upstream sensors are after the cut outs. If you can see if there is an o2 before the cut out but looking at the provided pics I doubt it. If thats the case thats why your getting the codes and the truck is running bad. The front 2 o2's read the mix in the exhaust and the PCM adjusts fuel and timing, if the cut outs are open the PCM is getting false info and the truck can not correct the tables. Snap a pic from the collector forward up to the head to confirm please.

FlaglerMegacab4x4 · Oct 23, 2013

Just a thought but shouldn't he also check his throttle position sensor? If the truck doesn't have steady acceleration that may be why.

KGBIGCOUNTRY · Oct 23, 2013

Im leaning towards the o2's hard because they effect how the truck runs all together. The jerky accel is just the PCM trying to keep adjusting while he is going, sometimes it gets close, other times it dont. Easy way to help figure that out is do a PCM reset and keep the cutouts closed and make sure they are not leaking and see what it does. Even a small leak close to the upsteam o2s can cause a ton of headaches.

Rough idle on 5.7 Hemi

Senior Member

Supporting Member

Senior Member

Senior Member

Supporting Member

Senior Member

Supporting Member

Senior Member

Supporting Member

Senior Member

Senior Member

Supporting Member

Senior Member

Senior Member

Attachments

Senior Member

Attachments

Senior Member

Senior Member

Senior Member

Similar threads

Forum statistics

Share this page