rpm is pegging at 2100 in park

[socal]

well its been awhile since i have had to come on her fro help. but here i am. i noticed about a month ago my truck was idling a little high every now and then when i would have it in park. yesterday it got worse. i came to a stop on the off ramp and it liked loped. it went from 700 down to like 300 rpm a couple times at stop. i looked at my fuel pressure gauge and it was steady so it was getting fuel . i put it in N and it was idling at 900 to 1000. i drove to my bank and tried resetting my throttle by turning it the engine off and turning the key back on and pushing the gas peddle down slow and letting it back up slow. it didn't lope anymore but it was still idling at 1000 rpm in park . i put it in drive and it would show 700 on rpm. i did some searching last night and most part i kept seeing its a bad crank sensor that is the cause. i replaced it about 30 thousand miles ago with a napa one. this morning i went to cummins to buy a new one and i noticed it was idling high to the point while driving it was like i had cruise control on . and when i came to a stop it was like i had one foot on the brake and the other foot on the gas peddle still giving it a little gas. i let the engine cool down and i washed the engine before i started changing the sensor. i pulled the old one out and installed the new one from cummins. got to start it and now it goes strait to 2100 rpms and it wont come down . i dont get any check engine light i hooked up my scanner and theres no codes. im gonna try putting the old sensor back in tomorrow to see if it drops the rpm so i can move it. any ideals what is the problem? i replaced the cam sensor around the same time i replaced the old crank sensor. i replaced the sensor on the trans also some time back. i started getting the tranny shift back and forth problem some time back and i replaced the alternator with a brand new one and that took care of that problem. the engine has been rebuilt about 20 thousand miles ago, i replaced the vp pump and lift pump and the apps sensor around the same time also. as a matter a fact the fass pump died just before the warranty ended and fass gave me a new that was about 2,000 miles ago. could it be my ecm taking a dump?

Edited December 14, 2017 by socal

[Mopar1973Man]

Remember as long as the APPS IVS (Idle Validation Switches) is telling it idle position then it all ECM software controlling idle speed detect from the cam sensor (later) or crank sensor (early). So the ECM attempts to make the engine idle at 800 RPM. The only thing I've found that may affect the idle performance is valve lash but this will not cause it to jump up 2,100 RPM. You might test for AC noise from the alternator it might be fouling the ECM ability to see the sensor correctly. 

[socal]

Can you tell me what exactly does the cam sensor and crank sensor do? 

Edited December 14, 2017 by socal

[Mopar1973Man]

Cam on the late series engine is the tach sensor. Crank sensor on the early series engines is the tach sensor. So both report the engine speed to the ECM so it can throttle accordingly for idle speed only when the IVS switch in the APPS is set for idle position.

[socal]

35 minutes ago, Mopar1973Man said:

Cam on the late series engine is the tach sensor. Crank sensor on the early series engines is the tach sensor. So both report the engine speed to the ECM so it can throttle accordingly for idle speed only when the IVS switch in the APPS is set for idle position.

Alright thanks. I just tried starting it and now the wts light wont come on.  And I get a check engine light. But no codes

1 hour ago, Mopar1973Man said:

Cam on the late series engine is the tach sensor. Crank sensor on the early series engines is the tach sensor. So both report the engine speed to the ECM so it can throttle accordingly for idle speed only when the IVS switch in the APPS is set for idle position.

My truck is a 1999 so it would be the crank sensor?  Is the cam sensor behind the vp pump? I remember changing a sensor there when I first bought it

[socal]

I changed the crank sensor back to the old one and it still shoots up to 2100 rpm.  So I would say it's not the sensor 

[Mopar1973Man]

Hmmmm... anyone around you with 2nd Gen truck you can swap ECM's??? If the problem swaps to the other truck then the ECM is damaged and needs to be repaired.

[socal]

so heres  a update turns out the problem wasn't my ecm or crank sensor. installed a timbo apps on my truck when i first got it. and when i set the idle screw i never put some loctite so after awhile it threaded in more and was making it idle high in park if i remember i think the timbo instructions dont tell you to put some loctite on the screw. such a simple thing to think of first to check on a old carb engine but when you think of engine that has a ecm and all that electrical **** its the last thing i thought of. hope this helps another member out.