Cranking and idling issues

[Eric Hodges]

my son bought a 2003-2004 1500 5.7 hemi. When we got it, it was leaking coolant in to one of the cylinders, but it ran fine. It wasn't over heating or mixing coolant and oil. It needed a few things exhaust manifold upgrade, front and rear main seals, the head gasket obviously. so we done all the repairs, get it put back in and go to crank it, it fires up runs for a few seconds starts spittin and goes dead. I fire it back up and i have to feather the throttle to keep it running. Everything sounds great and all, but the throttle isn't responding with my commands. so I scan it and get p2021, p2027,p2115, and p2116. well when we took the engine out my son cleaned the throttle body, so I assumed the faults were from the throttle position sensor messing up when he moved the blade or something. so i put a new throttle body on it, cleared the codes, go to do a throttle adaptation and when it tells you to cycle the switch at the end of the process, i turn the switch off and when i turn it back on the ecm will not come back on. the cluster and all the lights came back on but the gauges wouldn't move and it would not start. so sitting there scratching my head, I turn the switch back off un plug the scan tool, turn the switch back on and the ecm is back online. the gauges are moving the engine will now turn over. So I repeat the throttle relearn process and it does it again, the ecm will not come back on until I unplug the scan tool. so i do some research and says that more than likely it's due to a bad ground or voltage spike due to a short and its cutting itself off to protect it self. well i scan it again and the only codes that come back are the p2021 and p2027. so I am thinking that some where in the mix of putting everything back together, either I missed a ground wire somewhere cause on a side note the ground straps were all messed up. so i removed them and put new back, but it makes me wonder if i messed one, or if i have a signal wire that runs to my APP sensor that is shorted some where. I'm just trying to find out if anyone has any ideas, or if yall think im on the right track or not. just as a reminder it was fine pre pulling the motor out and doing the repairs. It will fire up like i said but you have to feather the throttle to keep it running, and the throttle doesn't respond like it should. If anyone has any advice I would appreciate it. Oh, sorry bout the bad grammer and punctuation, im just dumb ol'redneck mechanic from Alabama.We just found out what shoes are for last week. I always thought they were a weapon for your mom to throw at you.