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DanTheMan 08-30-2012 01:57 AM

1998 Ram 5.9 rough idle
Hey everybody! I got a 1998 Ram Sport with a 360 about three weeks ago. Ive noticed that after the truck sits for about an hour, it will idle really rough when I start it and it will feel really down on power and it will also backfire if I give it any gas. The problem goes away after like 15 seconds, but I have no idea what could be causing it. After it goes away it won't come back until after it sits for a while. Any help would be greatly appreciated!

1998ram2500 08-30-2012 01:56 PM

A little more detail would be helpful to be able to understand just how this condition develops and resolves. Does the rough idle start imediatly or does the engine have to warm up for a minute or two and then become rough? Does the rough idle last only for 15 seconds or sometimes longer? Is there any associated noises with the intake, perhaps a loud sucking noise? Does it happen whenever the engine is started "cold" or when worm as well?


DanTheMan 08-30-2012 04:45 PM

It will do it after it has sat for more than an hour and it will do it every time I start it after it has sat that long. It starts to do it after it has been running for about a minute or so, and will typically only last 15-20 seconds each time. I can make it stop by popping it in neutral and revving it way up. I havent heard any other weird noises other than the backfiring

1998ram2500 08-30-2012 05:50 PM

Something to try
Ok next time you start it cold let it run at idle until it starts to act up. Do not give it gas. Turn the engine off and then immediatly restart the engine. If the engine starts up and runs smooth for 30 seconds to a minute it is very likely your front O2 sensor. If that sensor is bad it will give bad info to the computer and the IAC will do wacky things until it reaches proper temp. I have the same year and engine as you and mine did this as well.

Here is the booger though. The front O2 sensor on mine was likely killed by the Plenum gasket leak that I have now fixed with the hughes kit. So if you only replace the sensor and do not investigate wether your gasket is letting oil get sucked into the intake then it will likely die again as you would be treating a symptom and not the cause.


DanTheMan 08-30-2012 10:50 PM

I tried it out and when it started to get funny I shut it off and restarted it and she fired right back up. I saw a video on how to change the Plenum gasket and it looks like a real pain in the behind. I guess that will be my next project lol. Thank you so much for your help Corey

RamOutlaw 10-15-2012 06:20 PM

I had a similar issue with my 01. She ran fine till one day where she started revving her self up when in park or just idling at a light. On my way home she got ridiculously quiet and felt like she died till I press the gas. Long story short I had my 02 sensor replace but she continued to rev when ever she felt like it( delt with the revving for close to 2 months and im talking about from idling at 700 rpms to 1500 while sitting), it was also like she would want to go out from underneath me with a jolt of power again only at slow speeds. Today I replaced my PCV valve and cleaned my throttle body. My throttle body was pretty bad so was the PCV. So far so good no rough idling. Fingers crossed!!

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