2001 Ram 1500 5.2 2x4 with 157,000 on it.

The truck is not my everyday driver but I do drive it 2-3 times a week, mostly short trip city-type driving. Over the past 1500-2000 miles or so, it has periodically been running real rough. Idles terrible after startup (RPMs bounce all over), then it clunks and sputters while driving like it's starving for gas or air and then when decelerating coming to a light the tach will bounce all over and it will stall out (also there is a noticeable gas smell when you get out of it). The first few times it happened the exact same way: Went for a long 20-30 minute highway drive and it was fine, parked for 30-60 minutes and when I restarted the issue happened. I thought maybe I had a bad tank of gas, so I filled up with a higher octane and added some water remover to the tank. Same issues kept occurring. I have found that if it sits for a couple days, the issue doesn't happen on startup. It's when I drive it and let it sit for a short period that it happens. I have also found that when I start up and it is running rough, I can typically shut it off and restart a few times and usually by the third restart it is fine. No check engine light during this whole fiasco.

In the past 2000 miles/6 months I have replaced: wires/plugs/distributor cap & rotor, downstream O2 sensor (there was a code for this), MAP sensor, IAC valve, throttle position sensor. I cleaned the throttle body. Changed the oil/filter. Changed the transmission fluid/filter (after I did this was the first time I had the issue but I can't see how that could be related). I have been using Red Line in the gas (ran a full dose and maintenance doses since). I also hit it with a couple doses of MMO in the gas.

I don't know if I just got a bad sensor or what, but the issue did happen before all of the replacements. Does this sound remotely familiar to anyone?

 

Something gets hot, and tries to fail. Probably cam, or crank sensor. Cam sensor is cheaper. Though given your symptoms, I would more suspect the crank sensor... possibly PCM......

Getting any codes by any chance? Also, gotta be careful with what brand sensors you buy. These trucks just don't really like aftermarket sensors..... especially cam and crank sensors. Mopar only for those. Same for the IAC. I had nothing but trouble with the one I got from the parts store, put in an old, used, mopar unit I had laying about, and my idle problems went away.

 

Maybe the ignition coil to

 

The tach getting stupid makes me think crank sensor.

 

You have a point there :b

 

If I comb my hair right, I don't think anyone will notice though.....

 

Thanks for the replies. Crank sensors are $110 new on Mopar's site. I'm going to see if I can get a junk yard part. Looks like they're $20-$50. Seems like an easy fix if that ends up being the issue.

 

Bought a MOPAR crank sensor (found one new for $70) last week. I was able to finally get it changed out yesterday. It was definitely not easy to get to. The two bolts holding it on are down behind the right valve cover. You can see them from under the car but can't get to them from there. From up top if you pull all of the plug wires on the right side and get them out of the way you can get at the bolts but you can't see them so you're doing it blind. The bolt heads are 1/2", but they also have a recessed hex head in them. The bottom bolt I was able to get with a 1/2" socket with a 4" extension and an elbow. The top one I needed two elbows and two extensions and it just slipped off again and again so I finally got a flexible drive extension with a hex bit and that worked like a charm. I used that to put them back in as well with a little duct tape to hold the bit and the bolt on and that made the process much easier.

I've only driven it once and so far so good. I'll post an update in a few weeks. Thanks again for the replies.

 

So the crank sensor replacement didn't fix the issue. Put in a new upstream O2 sensor a few days ago and it seemed to be running a lot better, but the issue came back today. I saved the original IAC, TPS and MAP sensors so I am going to clean them up and try swapping them out one by one to see if I got a bad aftermarket sensor. Talking with my mechanic a few weeks back when I was getting another car inspected he said if it wasn't something electronic/sensor related that it could be a bad cat.

 

What brand O2 sensor?

To test the cat, just remove the O2 sensor from the exhaust, and drive it. Yeah, it'll be loud..... but, if your problem goes away, there ya are. Trouble is, I suspect you will have to drive it like that for a couple days, if that's how long it took for it to start screwing up after the O2 sensor change.