1999 24 valve high idle and bucking at highway speeds

[Mopar1973Man]

Neither of those sensor control idle speed. Only IVS idle validation switch controls idle. When the APPS grounds the idle pin the ECM will control idle speed directly. The only sensor that controls idle speed is coolant.

[24vgarrett]

is there more than one coolant temp sensor the only one  have found is by were the top rad hose goes into the the cylinder head.

[24vgarrett]

So i got a mutimeter and put it on the battery and its dropping voltage at idle i then went and measure the alternator output and it was consistent so im losing voltage somewere 

 

[IBMobile]

 Check the cable that goes from the alternator to the PDC where the 140 amp fuse and from the other side of the fuse and the battery for high resistance or bad connection.. 

Has the W-T Mod been done?  See below.

 

[24vgarrett]

As to my knowledge no but I read it a little and it talks about the torque converter shuttering problem and my truck is a 5 speed but I will check that spice and see what it looks like and follow the wires

 

[24vgarrett]

at idle my voltage drops sometimes and you can hear a load drag the engine down a little and the lights on the dash and headlights dim i have a feeling this and my bucking have something to do with eachother. After a few seconds of the "load" it goes back to normal and it does it repeatedly the guage on the dash will go down to 11 or so volts then come to a little after 14 volts ive put a multimeter on the alternator while its idleing and no jumps or hiccups with the voltage coming out of the alternator.

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[IBMobile]

These trucks control units are very susceptible to not only poor grounds, weak connections at the battery, bad batteries, corrosion in the connectors but AC voltage from a bad alternator diodes.  If the AC voltage is high enough, >0.03VAC, It will cause not only automatic overdrive problems but other drivability problems to the point of ECM/PCM failure.  I strongly suggest you test for AC voltage with a quality volt meter, like a FLUKE multimeter, and read over that Ground Reference article.     

Edited February 1, 2020 by IBMobile

[Tractorman]

3 hours ago, 24vgarrett said:

at idle my voltage drops sometimes and you can hear a load drag the engine down a little and the lights on the dash and headlights dim i have a feeling this and my bucking have something to do with eachother. After a few seconds of the "load" it goes back to normal and it does it repeatedly the guage on the dash will go down to 11 or so volts then come to a little after 14 volts ive put a multimeter on the alternator while its idleing and no jumps or hiccups with the voltage coming out of the alternator.

.

 

It sounds to me that you are describing the normal cycling operation of the intake manifold heaters .  Combined, the two intake manifold heaters draw about 200 amps - that is why your are seeing the drop to 11 volts while idling.  When the heaters cycle off, the voltage returns to around 14 volts.  The heaters will continue to cycle until the engine coolant temperature rises to a specific value or when the truck has been driven over a specific speed - approximately 25 mph.

 

- John

[24vgarrett]

Ok thanks for clarifying that so now I’m just on the hunt for a bad ground correct?

[24vgarrett]

Ok so I unhooked the intake heaters on the drivers side battery and no more voltage drop but it still high idles but the bucking has completely stopped until I get to about 80 mph/2500 rpm

Edited February 1, 2020 by 24vgarrett

[24vgarrett]

So now my truck wants to idle at 2200 rpms all the time and won’t stop no matter what I do 

[Mopar1973Man]

Remember grid heaters will cycle still pull voltage down. Grid heaters draw 95 maps per element.