Newbie here so please be gentle. I have a 99 24v, 4x4 auto 134k miles that started idling at 1000 rpm's and has a miss to it. Happened out of the blue while wife was driving. Idle stays at 1k and misses unless put in gear. when put in gear, it idles @ 900 rpm and smoothes out under load of trans while in gear. Truck runs out great as long as its accelerating but when you let off throttle you can hear it miss. Fuel psi is 19 at idle with a air dog 100 lift pump. Truck is stock besides lift pump. Only code its giving is p0234 and I found waste gate stuck. All exh temps from exh man are within 40 deg f of each other. Iat, ect , and map look good on scanner. Batteries are 6 months old and test good. I have checked and cleaned grounds. I have a timbo apps about 1 year old. Truck doesn't smoke any out exh pipe. I checked for ac voltage and got a high of .030vac. Any ideas? What will make a cummins idle high? ecm? I have auto enginuity on my laptop to scan with. Please help!

Edited April 6, 20169 yr by Itaintez
forgot to add some info

Coolant temperature.

 

Idle is completely based off of coolant temperatures. So once the APPS set the IDLE IVS then the ECM software bases the idle speed off of coolant temperature. So colder coolant makes the idle higher and hotter makes the idle lower. I've got as far as hooking up a rheostat to the coolant sensor plug and cranked the coolant down to -30*F and had the idle cranked up to 1,800 RPMs and the went the other direction and crank it up close 230*F and the idle dropped to low 700 RPM.

 

Still in all the idle is completely ECM driven. So between the crank sensor and coolant temperature would produce your idle speed so if the crank sensor isn't quite right (flaky) or the coolant temps (bad thermostat) are off then you can get variance.

I got the wires on the vp44 that go to the timing solenoid covered with heat shrink. Started up the truck and it ran normal with no missing for about 8-10 mins, then the miss came back. Today I hot wired the vp44 and started it up. I still have the miss and if anything maybe just a touch worse. Does this mean that my ecm is out of the equation as far as the missing goes and that the vp44 is the reason for my rough idle?

So is idling below 800-850 a bad thing just because of the lower numbers or just because it indicates something else is worn or broke?

20 hours ago, Mopar1973Man said:

Actual programmed idle speed should be 800-850 RPM.

 

700-750 RPM is too low and not normal.

 

The only thing I can thing off your IVS switch is still on throttling position which would cause it to ignore idle software causing a higher idle RPM.

Thank you. in this case what do I NEED to do?

When I bought this truck an unskilled mechanic was installed the 165* thermostat and poor truck was running like that for a while till I changed it to 190*. is it possible that cause the problem (165* temp) and messed up the ECM?     

190*F is the proper thermostat...

 

6 hours ago, Sam53 said:

is it possible that cause the problem (165* temp) and messed up the ECM?

 

ECM is programmed device it can't be altered because off a thermostat.

 

I still think the APPS is still in throttling mode.

Anybody got ideas on my vp44 being bad from the tests I've done?

If you considering it then just do the BlueChip hot wire test then the VP44 is standing alone and no data feed from the ECM. Maybe you can still see RPM's... If so see if it changes. If it does change then the ECM is feeding it information to idle higher. Either coolant temperature or APPS sensor.

Yep I did the hot wire test, the idle is about 900 . I'm not  as concerned with the idle speed as I am the engine missing like crazy. Engine is still stumbling/ missing like crazy even when hotwired. So this means vp44.is bad, correct? Also I've checked for air at inj lines and I've got good fuel pressure spraying out when running. I've got some videos of the truck running. Is it better to post YouTube then share the link?

Yup, YouTube and share! 

Yeah, upload to Youtube and copy the URL to the post it will automatically embed to the post.

Edited April 10, 20169 yr by Mopar1973Man

Here is the youtube link to the video of my truck idling.

 

Yea that don't sound too good.

 

Sounds like could be a bad injector or maybe the cam shaft sensor is bad.

 

I really don't have any first hand experience with this but seems like it's something in the injection or timing aspect of it.

Video of my truck running with the vp44 hotwired.

 

Sounds like my truck while starting after priming the fuel system and purging the air from the other lines. Both the videos sounded that way, I am not thinking VP.

You can put the truck in gear and take off and as long as it's accelerating it runs normal. It will sound like the video on deceleration or at idle. If it was air in the system would it still run good under a load?

Sad part is with it "BlueChip hot wired" only leave the VP44 to blame for electronics. There is no feedback of ECM or any other sensor being the injection pump has no connection ot the ECM now. As for fuel its possible for air to be present and cause weird issues. I would consider pop testing injectors and checking the fuel supply for air. If those both check out then it going to be time for a VP44.

43 minutes ago, dripley said:

Sounds like my truck while starting after priming the fuel system and purging the air from the other lines. Both the videos sounded that way, I am not thinking VP.

 

That's exactly what I thought. If it was air in the system I have no clue what could be causing that much air to leak into the system and still let it run. 

Do you still have the stock injectors? Like Mike says it is probably time to pop test them and check the rest f the fuel system. If its not fuel related the VP is all that is left.

 

Just thinking out loud. Is it possible for the key in the pump shaft to deform and throw things off just enough to screw up idle and run ok under load? 

Exhaust temps coming out of exh ports at manifold are within 40deg from the least to the greatest at idle. If i had an injector not contributing, wouldn't I see that in a substantial drop in temp on that cylinder? Yes, as far as I know the injectors are stock. Vp44 has a reman sticker on top of it. It was this way when I bought the truck 5 yr ago. As far as key being off, I doubt it, it ran fine for five yrs.

Edited April 11, 20169 yr by Itaintez

Exhaust temps won't show you bad firing injector tip.