The temperature outside this morning was a balmy 59 degrees. The truck ran rough and all the symptoms are back. Drove the truck around town yesterday, the temp was around 75 and the truck ran great. I will get a vaccuum tester but wondering why a vaccuum leak would only cause it to run bad in cooler weather. I have already replaced the temp coolant sensor, no help.

 

From what i have read in the FSM, the coolant temp sensor is a primary signal for both fuel ratio and spark timing. Since you have already changed this with no good result, next thing is map sensor which monitors intake vacuum to provide basic air/fuel ratio control. But a vacuum leak could affect manifold vacuum resulting in overrich mixture and flooding the engine. is your exhaust outlet pipe really black?
before you swap Map sensor, you may want to verify what vacuum signal the sensor is getting.
it could be that when the engine sits overnite, a leak may be due to manifold fully contracted when engine is cold, and as the engine warms, the leak is pinched off to the point that the rest of the engine controls can compensate and engine runs acceptably. A leak could be from hoses or manifold or gaskets.
Just a theory at this point, but a vacuum gauge is probly cheaper than buying the full set of sensors and swapping these out one at a time.
just my 0.02

 

I should have clarified the fact that even after the engine warms up in cold weather it still runs rough with all the symptoms explained earlier. It either runs good in warmer weather and runs terrible in cooler weather regardles of the engine temp. I will get a vaccuum tester and see what I get there. Thanks

 

just for your reference, we measured ~16" on our 3.9 magnum engine at idle speed last weekend

 

Are you sure you replaced the correct one? There are 2. One for the computer and One for the gauge.

 

The one I replaced is for the computer. I pulled all six spark plugs this afternoon and four out of six were black and wet. It appears that the wetness on the plugs was gas. I checked the vaccuum for the map sensor and it was good. I bought some component cooler yesterday and used all troubleshooting the sensors with no luck. I did some research on the map sensor and it has a small electronic pcb that detects the barometric pressure/weather. I am having a weather problem. I sprayed some of the air left in the component cooler can into the vaccuum port of the map sensor. The air was not cold but cool. I sprayed my hand first, the coldness was used troubleshooting yesterday. I started the truck and had the same backfire through the throttle body that I had when driving in cold weather. I have ordered a map sensor and will pick it up tomorrow. Not sure if my troubleshooting technique was right for this but I will know more tomorrow.

 

hope this works for you.
i was just reading the FSM for the test procedure for the MAP sensor. do you have a voltmeter to check it out after you change it to see if something changes?

 

I picked up a new map sensor at the auto part store this afternoon. The box looked like crap and the sensor looked used. Installed sensor and immediately started having problems. The temperature was 82 degrees and this sensor acted just like the original sensor did when the weather was in the 60's. Checked the computer codes and found that the new sensor created a code of 13 in the computer. This sensor is definitely bad. Took sensor back, they had to get one from another store. The quality of the new sensor was evident as soon as I laid my eyes and hands on it. Installed the new map sensor and the idle seemed be where it should be. I have had a problem with this truck having a high idle for as long as I could remember. It is 8:00pm, I just took the truck out and the temperature is around 65. The truck ran great. I will take the truck out about 5:00 tomorrow morning for another test. I think my problem is cured. I will know more tomorrow morning. I will post again tomorrow to verify that the problem is fixed. Thanks for all the help. I think it is great to have a forum like this to exchange ideas.

 

I hope you have found the solution to your problem! Glad to hear you may have it resolved, and personally I am looking forward to tomorrows 5am test run. Good luck and keep us posted!

 

The temperature outside is currently 49. My problem is back. A lot of backfiring through the throttle body and running like crap. No computer codes. I am at a loss. I think it still has to be a sensor that is sensitive to cold weather. This is starting to drive me crazy. Why only cold weather and not all the time? Thanks