I've searched all over and most people have the opposite problem (runs bad when warm) mine runs bad when cold...

2001 Ram Sport 4X4 5.9 (just hit 139,000 last week)...
P1391 code...
I'm in Michigan so mornings are cold (take my grandson to the bus every morning) let the truck run in driveway to warm up and it idles a little rough and stalls every 3 or 4 mins until it's driven...
When I hit 40 to 50mph (sometimes slower) it'll spit, sputter, falls on it's face, can hear what I would call spark knock, but no other sound from the engine, it's spark knocking but it's not running! (has flowmaster exhaust you hear it run)
Once the truck is warm it idles great and runs fine all day long....I can let it sit all day long after that morning drive and start it at 10pm, and it'll run fine....let it sit overnight and same issues until it warms up....throwing a p1391

I spent the money at the dealership and got crank and cam sensors from them...
all sensor wires appear to look good...
I did put a new IAC valve on it, that appears to have fixed the stalling in the driveway problem only! (the old one was carboned up pretty bad).

The strange "to me" thing....
If I do a battery reset (unhook battery to clear the check engine light/reset the pcm?) in the morning before I start the truck you'd never know the truck had a issue....it'll start and run fine all day and night....let it sit overnight and depending on if I unhook that battery or not before starting the truck will determine how the truck is going to run.


I would like to mention the truck has never got up to normal operating temp (VIA the temp gauge) 210 is halfway on the gauge and the needle never gets even halfway to the 210 mark....(heat is always luke warm at idle)
However, I've noticed after a battery reset, the needle on the gauge works and the truck reads around 195 on the gauge (if I was to guess)....and the heat is actually warm at idle!
Skip that morning battery reset, and it runs bad until warm...engine light comes on p1391....temp gauge goes back to not reaching operating temp....
Battery reset every morning and you'd never know the truck had an issue...


Any Ideas on what direction I should go next...
would one of the temp sensors trigger the computer to acting funny causing the morning issues and a p1391?
Have any other parts triggered that code? MAP sensor?

any help is greatly appreciated...

 

Your truck only has one temp sensor, and it reports to the PCM. The PCM then tells the cluster where it should put the various needles. Usually, it's pretty reliable...... usually.....

On the cold start days when you DON'T disconnect the battery, does it run ok for a bit, and then after a couple minutes start getting wonky? Or is it wonky right out of the gate?

Did you clean the throttle body REALLY well when you changed the IAC?

Do you have a scanner that can read live data? If so, see what the PCM Thinks engine temp, and intake air temp are, when it's running funny. Still getting any codes?

 

P1391 is a cam/crank sensor intermittent problem and the temp sensor is off as well so I'm thinking it's probably not an issue with a particular sensor but some electrical gremlin makes them read wonky. As HeyYou wrote it would be useful to know what all the other temp sensors read, and what voltage the PCM sees. On a Michigan truck I'd look closely at the grounds.
The heat only being lukewarm is somewhat puzzling. If the PCM is fooled by low temp readings it would add more fuel but I'm not sure that would keep the actual real engine temp down so much that it would affect the heat.

 

Well it IS a second gen ram...... known for having troubles getting all the air out of the heater core.... and leading to ****-poor heat.

 

#1- cold starts if in driveway at idle it'll take a few mins before acting up and idle gets rough (will almost stall but doesn't)....if cold start jump in and drive it's almost instant once on the main road (through the subdivision it's fine).

#2- best as I could with it still on the truck...

#3- no scanner....unfortunately, my only access to a scanner is autozones scanner...

I really don't want to take my truck in....I've never paid someone to fix my vehicles...all this electronic crap is making it almost impossible to avoid now a days...
I've read all about this darn code....It's like chasing a ghost

 

That's what I'm afraid of...That gremlin.

Going to be nice here tomorrow, I'll look the wiring over again and check the grounds....This winter did hit me hard by the gas tank lid, but the truck is in pretty good shape for a Michigan truck (I highly doubt it was in Michigan it's whole life) I do need to pull that carfax

 

Unplug the front O2 sensor, and see if at least some of your problems don't go away.

 

Wanted to give it another day before replying....

Thanks to @DerTruck for lighting a fire under my A$$ and got me out there looking for that gremlin again...

I do believe I found my problem....I didn't wait for the next day, I went out that night and looked the truck over again....started at the sensors and worked my way around...all grounds looked good....I never did check the PCM connections for corrasion went to unplug it and noticed the two plugs on the left were nice and tight, the one on the right was moving when i touched the wiring harness .....Unplugged it and the plug is fine, the little tab on the bottom of the PCM that the plug clips onto is broken (I've had this truck over 2 years). So, I tied a string around it, so it was nice and tight and didn't wiggle, that next morning I did NOT reset the battery and the truck ran perfect all day and night....This morning same thing...cold start (no reset) a 30 mile drive after the bus stop ...runs perfect with no engine lights or codes (two mornings now) ....

My question now...
I don't care for the string .....are these plug and play? or do I need to buy one and take it in for programing too? (If yes, I'm assuming they have to put it in or I'll be towing it to the programmer?)

 

Yeah, 01 needs to have the VIN programmed into the PCM. The truck will run without it, just the ABS and SRS systems will be unhappy.

 

Personally, I would not be going through the trouble of replacing the PCM. Some pretty zip-tie work or maybe even fab a hold down across the connectors should do the trick.