Engine/Transmission (1998.5 - 2002) Up and down idle when cold

[waldo]

It just started a couple of weeks ago. When every the trucks sits overnight or all day a work, when I first start it more so in drive the idle drops a bit then recovers while warming up. Drive around the block and the idle is normal. It dosen't seem to matter what the temp. is outside. When the truck is drivin, its back to normal. Hoping for so insight. Thanks

 

[pro99]

What year truck? How many miles? It may just be the heaters kicking on and off. Or may need a valve adjustment?

 

[waldo]

Sorry 99 24 valve 145,000 miles. Its not the heaters, I known that sound. This is faster in the up and downthen the heaters.

 

[pro99]

Before spending any money I would perform a valve lash adjustment, Can you see what fuel pressure is doing?

 

[waldo]

Fuel Pressure Is 15 At Idle Same As Always. Do You Really Think Its The Valve Out Of Adjustment.

 

[Gary - K7GLD]

Grid heaters are one source, another is the A/C cycling to control humidity and keep windows clear of inside moisture.



You could pull the related fuses/relays to verify...

 

[SKneeland]

i know when my batteries start going south the grid heaters can really drawn the idle down