My '08 Ram has a little under 59,000 miles on it and has been well maintained. But for some time, it has seemed to drive differently almost every time I start it. Some days it will run great, and it will get decent fuel economy (15-16 mpg); other days it will run like it's pulling a 5,000 trailer and get horrible gas mileage (10-11 mpg). Some days it runs great in the morning, and terrible the next time I drive it. I can't find any rhyme or reason to the problem.

Some of the specific symptoms I've experienced are:

-Occasional extreme lack of power going up hills from a stop (I'm talking about struggling to go 5 mph until I mash the accelerator pedal almost all the way to the floor). Once I mash the pedal, it will take off like a rocket. This is dangerous.

-Sudden/brief surge in idle when coasting

-Occasional lack of acceleration

-Occasional poor fuel economy (as already mentioned)

I have had absolutely zero Diagnostic Trouble Codes, so it's tough to diagnose this, but I am thinking there is either a problem with the MAP sensor, the electronic throttle control system/throttle body, perhaps a vacuum leak, or maybe (very unlikely) a failing O2 sensor. I did a vacuum test and got exactly 21 in Hg at idle - is that normal? I have also noticed that my scan tool shows the engine is at 20%-30% load at idle, which seems high, but I have no idea if that is normal or not.

I welcome any advice as to how to troubleshoot this. The vehicle is under warranty through CarMax, but they seem completely incapable of diagnosing any problem that isn't associated with a DTC. So, I am likely on my own until I get a DTC.

Thanks in advance for any help!

 

Start with a tune up. And throttle body cleaning. A can of sea foam in the tank.

 

The truck got a tune-up at ~45,000 miles; the problem was present both before and after the tune-up. I regularly run Sea Foam and Techron in the gas (I usually alternate between the two - one can each oil change), and I use only Tier 1 gas.

The throttle body was cleaned at about 53,000 miles with no noticeable effect, but I plan to clean it again. Thanks for that suggestion. Unfortunately, I suspect something else is going on.

 

Perhaps a TPS issue or even a EGR valve hanging open, although those usually throw a code.

Might be best to have the dealer drive it while acting up with a Star Scan too to monitor all perimeters. It might cost a little bit, but better than buying unneeded parts trying fix it.

 

I have done a few things since my last post and I think my issue was probably partially related to all of them.

First of all, I replaced the MAP sensor. That seemed to help some with the random extreme sluggishness when accelerating from a stop up an incline. However, the problem still persisted to some degree, so...

After letting CarMax screw around and find nothing a couple of times, I finally just took the truck straight to the dealership and explained to them the problems I was having. They called back later the same day and said they couldn't recreate the symptoms I described and wanted to keep it another day. The next day they called again to say they had found a technical service bulletin (TSB) about the MDS system causing the problems I described, so they re-flashed the PCM. I had wondered if it had been an MDS problem all along, so that made sense.

I picked up the truck, and while it did seem to be driving slightly better, something still didn't seem quite right. Throttle response and shifting seemed odd at times. So, extremely frustrated, I came back here and did some more research. That's when I found the thread about grounding the throttle body (https://dodgeforum.com/forum/3rd-gen...ng-the-tb.html). I had never heard of doing such, but decided at a total cost of $0 and basically no downside, it would be stupid to not give it a try. So, I found a length of 12 gauge THHN electrical wire and some ring terminals, and installed it. So far, I have to say that I have been extremely pleased with the difference this has made.
As others noted, the idle has smoothed out significantly, and the throttle response, and (more noticeably in my opinion), the transmission shift points seem more precise and well-timed. Before I installed this ground wire, the transmission seemed to wait too long to shift. Now, it's very smooth and quick.

So, to summarize...I'm not sure any one of these things solved the problem by itself, but as a whole, these small things seemed to have helped my truck run much, much better. I am thrittled, as I had gotten so frustrated that I was starting to consider getting rid of the truck. Now I can enjoy driving it like it's supposed to drive!

Thanks for everyone's input and for the incredible wealth of knowledge on this site.

 

I think i will also ground my throttlebody. i have some of the same problems.