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Random Rough Idle

18K views 12 replies 5 participants last post by  piper18 
#1 ·
2004 ram 3.7 5sp 75k miles

I've read a lot of similar threads but nothing really hit my problem dead on

I've had the truck for about 6 months, about 2 months ago I came to a stop and the engine idle dropped to around 400 and was shaking hard, (normal cold idle is 1000 warm is approx 700) then it cleared up in a few seconds with out me doing anything before taking off, then a few weeks after that it did it again, if I gave it gas it would rev up fine but drop to 400 again with rough idle and then cleared up on takeoff. the last 2 times it did this, again weeks apart, it seemed worse, I thought it might die but never did, as I took off it run rough and barely accel. and the engine light was blinking but as soon as i got over 2500rpm it cleared up and took off like a bat out of hell.

The hesatation reminds me of a 86 ranger i had that got moisture in the fuel a lot but it had problems all the time, not intermittently. I have a short drive to work so it never acts up cold, only after it warms up.

This may not be connected, but when I got the truck, I noticed it started knocking a bit under 2000 rpms with moderate to heavy accel. engine code said misfire cyl 1, so I changed the plugs, probably the first tune up it had,fixed that problem. I'm the second owner, amazing the truck didn't act up until after I bought it.
I wonder why all the problems clear up at high rpms? I would think it would stutter all the way through the rpms if it had a real problem.

The truck has always had a slight rough Idle just enough to let you know its running, most vehicles do, the idle I'm talking about feels like its going to shake itself apart or something. The only thing I could compare it to is that ranger. One cold morning I started it, it didn't want to run, gave it gas to keep running but i swear it felt like it was running on 2 cylenders. or compare the shaking to an earthquake

back to the dodge
just did the key trick, no codes.

What could be causing this problem?
 
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#2 ·
I may have solved this. I filled up and add two bottles of stp fuel treatment due to the 30+ gallon tank I got. I guess it worked. that stuff cleans injectors, removes moisture etc. well, until next time.
 
#3 ·
Nope, did it again today, worse as ever. In about a 10 minute time span, I'm driving along and then it starts to bog down and run rough, engine light flashing. when I came to a stoplight it idles real low shaking truck but didn't die. then I take off and it runs real rough and then straightens up a few seconds and starts running rough again. about 2 minutes from my house it straightens up again all the way home it's fine like nothing ever happened. did the key trick, no codes. Confusing as hell. Could it be moisture in the fuel? I'd change the fuel filter if it wasn't in the tank. If I had a bad sensor somewhere wouldn't I get a code? Any one have this problem?
 
#5 ·
Sound like the throttle body needs to be cleaned or EGR valve.
 
#7 · (Edited)
OK, this morning, I started it up and the engine light stayed on. the whole trip to work was pretty good it only had slight hesitation a few times but barely noticable. When I got to work I did the key thing, it said P 0300, I looked up my haynes manual. It said misfire multiple cylinders.I put a bottle of gas line anti-freeze/water remover in to eliminate that variable(I hadn't added any this tank). I drove it a couple miles to get lunch. it seemed fine for the most part, just a little hesitation around 1400 rpm's. I stopped at the store on my way home afterwork. It drove fine except the engine light was on(I'm not extremely concerned because i know why) first and second gear are fine, third at about 1400 rpm's it hesitates and then fine in fourth cruising at 1500. I noticed if I baby it in third it won't hesitate but if I give it about half throttle it does. I wonder why?

I can't believe its the sparkplugs, they only have 2k miles on them. Its cold this time of year so I'm afraid it will have to wait til spring to clean a throttle body or egr valve unless I can do it in 15 minutes. How much would a shop charge?
 
#9 ·
Today I left early this morning. It was dark, rainning and cold. If a vehicle is going to act up, this is usually it. But it didn't. Drove all the way to walmart with the engine light on but it drove perfectly fine. when I left walmart the engine light when off. seem fine now. I guess the ISO-HEAT water remover/antifreeze worked. which leaves the question:

Why do I have moisture in my fuel?

if that is the correct conclusion.
 
#11 ·
So did you say you did a tune-up on it with new spark plugs and everything?
 
#13 ·
check oil levels in the rear end and tranny.
 
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