I just took over payments for my brother's Dodge 1500 4.7 Magnum and have been having idle/RPM problems every since. When you start it even or put it in park after a drive, the idle is erratic going from 500 to 1500 RPMs. It just seems to go up and down randomly. Sometimes it would even go low and die at a traffic light. After reading the forums I thought it was the IAC. First we cleaned the one that was on there and it worked for almost a week, but the problem came back. So I spent $80 on a new one and it seemed to fix the problem for almost two weeks.

But then it started doing it again, the erratic idle and dying at traffic lights. So my brother listened and said the fuel pump didn't sound like it was working properly. Well he took the tank off and replaced the fuel pump. Well the problem is gone now, but now the fuel light is on, as is the check engine light.

He did specifically ask for fuel pump for the larger tank, but thinks they might have given him the wrong one. Not sure yet. Funny thing is the truck is idleing and running perfect now, but the gas gauge does not work and the check engine light is on.

So if anyone has any experience or insight they can offer then I would appreciate it.

 

Kinda sounds like the sending unit was not reconnected.

You might try resetting the computer. Find the "PCM" fuse and pull it. Get in the truck, close the door and buckle the seat belt. Turn the key to "on" and wait for the chiming to stop. Turn the key off and reconnect the fuse. It'll take a bit longer to start, but that's normal.

The code may clear and it may come back. If so, take another look at the sending unit connection.

 

My truck came with the 26g tank and I swapped it out for a 35g tank. The only difference between the two is the length. The diameter is the same so the pump will work fine.