The only vacuum hose diagram I can find is for the evaporative emissions system. When other routing diagrams are available, there are usually up to a dozen variations depending on options and engine configurations. For that reason, it is best to defer to the diagram under the hood. Chrysler usually puts that right on top of the radiator shroud. If you can find that, it will be the correct diagram for your truck.
The vacuum hose for the power brake booster will be a rather large one, as in almost an inch in diameter. It runs from the check valve plugged into the front of the booster to the intake manifold. On the manifold, it may go to the top of a "tree" that has additional, smaller ports on it for the other things like the cruise control servo.
As for how the engine runs, the IAC valve doesn't affect that. That is the same physical part used by GM, but in Chrysler terms, they call it the "automatic idle speed", (AIS), motor. It only controls idle speed. It is not a spinning motor as you'd normally think of one with brushes and spinning armature. Instead, it has four coils of wire that get pulsed with varying voltages and polarities by the Engine Computer, to rotate the armature to a specific point. The armature can be rotated roughly a total of ten revolutions. As it rotates, it retracts or extends a threaded shaft, and that adjusts the position of a pintle valve that sits in an air passage around the throttle blade. As the computer retracts the valve to let in more air, it increases the length of time, (in milliseconds), that it pulses the injectors open. That adjusts the fuel and air to adjust idle speed.
You can view the number of idle "steps" the computer has calculated is needed to maintain the desired idle speed, on a scanner. The range is from "0" to "256" steps. For a properly running engine, I've found step 32 is typical, and for one misfiring cylinder on an eight-cylinder engine, somewhere around step 50 can be expected. If you find it on step "0", and idle speed is too low, the computer hasn't relearned "minimum throttle" after the battery was disconnected. If that becomes necessary, to meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.
Before minimum throttle has been relearned, the engine may not start or run unless you hold the accelerator pedal down 1/4". It will tend to stall at stop signs, and you won't get the nice "idle flare-up" to 1500 rpm at start-up.
There are three other ways to find the vacuum diagram if it's missing on your truck. The best is to get a copy of the factory service manual. You'll find them on eBay at quite reasonable prices. The second way is to visit a pick-your-own-parts salvage yard. Take a camera along to photograph the diagram, but be sure to find one on a truck that had the same engine.
For the third way, I did a Google search, but those usually leave me frustrated as they bring up all kinds of diagrams for unrelated brands, years, and engine sizes. You'd have to scroll through dozens of diagrams and hope to find one for a 2002 Ram with 4.7L engine.
Sep 4, 2026 at 4:30 PM
