Rough Idle / Hesitation on acceleration

2005 1500 w/ 5.7L Hemi

Hey all. Hope I can get to get some help with a problem I've been trying to work through for a couple months now. When I start the truck the engine runs smooth when in either Park or Neutral but when in Drive the idle becomes rough and verges on stalling. As well, the engine hesitates on acceleration. Though typically the engine evens out a bit when up to constant speed ( highway ) there are times when its in a bad way when I have to stop the truck because of surging/hesitation. I also get engine codes. I always get a P300 code (Random cylinder misfire) and depending on the day various others including P0175 (System too Rich) or P0151 (O2 sensor low voltage). I even get the occasional backfire pop. Things I have done include removing and completely cleaning out the throttle body and replacing the air flow and MAP sensors.

With all the above being said there are other interesting facts which lead me to believe it may be electrical in some way.

When I disconnect the battery for 10 minutes and reconnect, the truck runs great - no rough idle or acceleration issues. And then after a week or two the above the rough idling/acceleration/codes return. At first I thought it was because each one of the solutions (cleaning throttle body, installing new sensors) fixed the problem but I now know that is incorrect. The fact is that I unhooked the battery in each case and THAT was why the truck ran better for a while. So I have been disconnecting/reconnecting the battery every couple weeks to get the truck to run right.

My guess is that it is electrical in some way but I'm not sure where to go from here. Somehow disconnecting/reconnecting the battery clears something out but over time whatever was cleared out gets fouled and the truck returns to running like crap.

Any help appreciated! THANKS!

Sounds like a bad O2 sensor. Before replacing it you could swap the two front O2 sensors and see if the code moves over to the other side. If it doesn't I'd look at the wiring.

RonJon '06 said:

Sounds like a bad O2 sensor. Before replacing it you could swap the two front O2 sensors and see if the code moves over to the other side. If it doesn't I'd look at the wiring.

Click to expand...

I find it odd that disconnecting the battery does anything at all. Generally being that the truck is so new and OBDII, disconnecting the battery shouldn't reset anything.

Sent from my SAMSUNG-SM-G930A using Tapatalk

I'm thinking it may be the ECU that gets cleared due to battery reset but gets fouled again. Would love to hear if anyone else has had this problem or can rule the ECU out as that could a pricey fix.

SteveRam said:

I'm thinking it may be the ECU that gets cleared due to battery reset but gets fouled again. Would love to hear if anyone else has had this problem or can rule the ECU out as that could a pricey fix.

Click to expand...

Yea this method used to work with 90s and earlier vehicles because they used to have OBDI computers that reset as battery is disconnected. However OBDII systems generally stay on standby even without a battery saving trouble codes and readings from sensors(kinda like when a laptop goes dead but when you plug it back in within a couple hours, none of your work has been closed or disturbed because it's been on a low battery standby ). However that's beside the point. If your getting a code for 02 sensor then start there. We all know that air fuel mixture make engines studder and idles rough. The o2 sensor is a big part of the fuel ratio equasion that you truck is constantly doing.

Sent from my SAMSUNG-SM-G930A using Tapatalk

12ValveBrandon said:

I find it odd that disconnecting the battery does anything at all. Generally being that the truck is so new and OBDII, disconnecting the battery shouldn't reset anything.

Sent from my SAMSUNG-SM-G930A using Tapatalk

Click to expand...

Disconnecting the battery resets the adaptive memory.

Maybe OP has a failing O2 sensor and the adaptive learning is trying to compensate for it? Anyway I'm with you, I'd go after the O2 sensor.

Thanks RonJon and 12Valve. I'll look to replace O2 sensors and report back.

SOLVED! So in the end it was the O2 sensors. Specifically, Bank 2 Sensor #1. I had replaced Sensor #2 last year so I did not replace that one. Had an absolute bear of a time getting the darn thing off but all is good now.

Thanks RonJon and 12valve. Your help much appreciated.

Steve