Idle Speed Suddenly Very Low, 300 RPM

[Ol'Jim]

2002 HD 2500 6.0 - Pulled into Wal-Mart, everything was fine. Came out 20 min later, started right up, but felt like it stalled, it was actually still running, (barely). Shut off, restarted, same. Used pedal to bump idle up to normal 500-600 RPM, it was smooth, no misfire or roughness. Drove home, approx 5 miles, and had to keep the idle up at every stop.
Could be IAC? How can I test it/What checks can I do in the darkness, by flashlight? No garage, and no help handy, but I do have tools, and basic test light, dmm, etc. First thought was fuel pressure, but it runs fine going down the road.
No lights or codes.
Thanks in advance for any advice.

[j cAT]

Originally Posted by Ol'Jim

2002 HD 2500 6.0 - Pulled into Wal-Mart, everything was fine. Came out 20 min later, started right up, but felt like it stalled, it was actually still running, (barely). Shut off, restarted, same. Used pedal to bump idle up to normal 500-600 RPM, it was smooth, no misfire or roughness. Drove home, approx 5 miles, and had to keep the idle up at every stop.
Could be IAC? How can I test it/What checks can I do in the darkness, by flashlight? No garage, and no help handy, but I do have tools, and basic test light, dmm, etc. First thought was fuel pressure, but it runs fine going down the road.
No lights or codes.
Thanks in advance for any advice.

low idle you have to check for fuel pressure. you need 53 psi to 62 psi.

this will also reveal any fuel regulator issues. fuel filter etc.

make a vacuum leak and see if the idle increases to 1100 rpms. then it could be the IAC. the IAC increases air to the engine to increase RPM , but you need fuel. the computer varies the injectors opening but you need the pressure . if the pressure is 50 psi the engine will run but at a low idle.

with no check engine light fuel pressure is big !

[Ol'Jim]

Thanks j_cAT, at least I was thinking along the same lines as you were.
Went out this morning to start up, and just a "click". Volts were good when key was first turned on, approx 12.5, but when turned to Start, the click, then everything went dark. Battery negative cable was a bit loose. (Darn side terminals). Tightened it up, and now all is well. I remembered just before I got to Wally World last night, I had hit the mother of all potholes. (Had not been down that road before, now I know). Roads are rough as hell around here, thinking that must have done it. Would not have figured that would cause my low idle RPM issue though, so I will keep an eye on things.
Thanks again, -Jim.

[j cAT]

Originally Posted by Ol'Jim

Thanks j_cAT, at least I was thinking along the same lines as you were.
Went out this morning to start up, and just a "click". Volts were good when key was first turned on, approx 12.5, but when turned to Start, the click, then everything went dark. Battery negative cable was a bit loose. (Darn side terminals). Tightened it up, and now all is well. I remembered just before I got to Wally World last night, I had hit the mother of all potholes. (Had not been down that road before, now I know). Roads are rough as hell around here, thinking that must have done it. Would not have figured that would cause my low idle RPM issue though, so I will keep an eye on things.
Thanks again, -Jim.

low volts to the fuel pump will do it. bad grounds also. shock does effect the fuel pump when they get old. with low fuel pressure and it will not, run hitting the bottom of the tank usually gets you going for a short time to move vehicle ,,, possibly get home .