I have a 1998 Dodge Ram 1500 4x4 and I find this odd and extremely frustrating. My truck has a very hard time starting. When you turn the key the engine tries to turn over but it won't without giving it gas. When I give it gas and it finally starts, the truck will die as soon as I take my foot off the pedal. However, when I apply the brakes, play with the gas, and shift it to another gear and back to park, sometimes it will stay running on it's own. I got a P0720 code which is the output speed sensor (which I replaced today) I figured it was a fuel pump/filter issue so I tested the fuel pressure and it shown between 50-60 psi but it was bouncing all over the place. I charged the battery and that wasn't it either, though amperage is all over the place as well. The wiring on the battery is kinda screwy so I'm wondering if it is a bad ground. I'm also wondering if the fuel filter/strainer is clogged up since I did use two bottles of fuel system cleaner this week. I just don't know what to do and I have only a little bit of cash to play with.

Does anyone have any advice or information that could help me?

 

did you reset the computer after replacing the sensor?

 

idle speed is controlled mostly by the IAC (idle air control) with some interaction with TPS (throttle position sensor). remove air filter and watch the iac in action - to see if it moves in/out to achieve (or hunt for) idle speed. remove the IAC and clean the pintle and port in the throttle body that it goes into to. that port is your idle air path, so it must be open and not gunked up.

don't push, pull, or twist the IAC pintle. you'll break it.
other than cleaning of carbon or sludge or gunk, they are not serviceable.

new one's are available at any parts store, but cost $40-50 each.
you might pull one at a junkyard for $5 or so.

sounds like your fuel pressure and fuel filter is ok at 50-60 psi. that's right on target of 49.

sounds like battery is iffy. clean all terminals, grounds, etc. our trucks will not idle right if the battery voltage is not at or greater than 12 volts not running and 13-14-15 volts when running. check with volt meter.

 

I went out there this morning and she started right up (no throttle interaction) after a few seconds of rough cranking. I shut her off about 5 minutes later and it wouldn't start again without an open throttle.

As far as the battery, it looks like someone mickey moused the connections, it's definitely not factory. I did clean the terminals and reconnected the wires to their clamp and it did nothing. If it's a battery issue, it seems like it would be the wiring.

It ran like a champ until a few days ago. I didn't notice any increasing symptoms of any problems. I spoke to a mechanic about it and he says it could just be the IAC valve.

Here's basically everything I've done:
Tested the fuel pressure.
Replaced the output speed sensor underneath as I was getting a code P0720.
Removed and tested the throttle positioning sensor, voltage was very jumpy.
Removed and cleaned the air filter, inspected the exterior of the IAC valve.
Disconnected and cleaned the battery terminals, reconnected the wiring to their clamps and reconnected the battery terminals , then I put a battery charger on it for about 3 hours.

 

Replace the TPS. That isn't right.

Pull the throttle body. Remove the IAC motor, and clean the pintle, and the passages in the TB.

Find out why your voltage is all over the place, and fix it.

 

sounds like it might be a stuck MAP sensor. Pull the MAP sensor out of the throttle body and see if it is corroded. You can clean these but they are not serviceable. I recently pulled mine because code 14 popped on my dakota and it literally fell apart in my hands. Waiting for a new one from auto store to come in. My dakota would start and then cut out after awhile. It would surge and buck whn trying to accelerate. Thought it was the distributor pick up sensor. Will know for sure when new part arrives.

 

check the battery wire that goes to the starter, some times they are close enough to the engine to cause trouble

 

I fixed it! It ended up being only a bad ground. I unscrewed and cleaned off the body ground and scratched some of the paint away under it and did the same to the one on the motor, except I added primer to that one. I was just messing around and killing time trying to think about what it could be and boom, she started right up and I haven't had a problem since.

I am going to replace the TPS and the MAP sensor as she feels a little sluggish on the get-go, but at least she's running and can get me to work.

Another issue I want to address is the truck sorta "jumps" into the next gear when I'm taking a corner and I pull straight. You can feel the RPMs increase like you're stepping on the throttle in neutral but then she kicks into gear. It's rather concerning. Any ideas on what that could be?

 

don't replace the MAP. its expensive and seldom (as in almost never) goes bad.
TPS and IAC are common failures.

not starting without pressing the gas pedal is an indication the IAC is not working right, which could be due to failure, or low battery voltage, or bad ground, etc. its the IAC's job to control the "idle air" around the closed throttle plate. when you press the gas pedal, it opens the throttle plate and bypasses the entire IAC function.

excessively hanging in a lower gear until high rpm's is an indication of needing to adjust the TV (throttle valve) cable. there's a how-to in the faq's.

 

Low ATF, or the filter has come loose. When you turn a corner the fluid sloshes to the outside of the turn, leaving the pump to suck air so line pressure drops to next to nothing and everything that's supposed to be clamped (bands, clutches) lets go.