I just bought this truck and I’m having trouble tracing a misfire. I replaced plugs, wires, and IAC. The truck idles high even when warm (about 2000 rpm) and will randomly start misfiring so bad the entire truck shakes. Then out of nowhere it will run fine. I’m pretty sure I have a vacuum leak somewhere because when I increase acceleration (any speed, any RPM) the air conditioning will die down almost like the a/c is off. Any tips on where to go next?

 

Welcome to the forum

Warm up engine, and turn AC off, i.e. put controller to OFF, not just in panel or defrost

With engine idling, unplug the 2 wire connector on IAC Valve, Idle should drop to 500rpms, barely running, if not you DO have a vacuum leak and a larger one

With IAC Valve still unplugged, pull off power brake booster vacuum hose and plug its intake port with your finger, if no change in idle then put hose back on and pull off PCV Valve hose, same thing
Repeat with each vacuum hose connected to intake manifold to see if any of these hoses, or device at the other end of the hose, is leaking

If not then get a spray bottle with soapy water inside and start spraying it around the lower then upper intake manifolds, engine will stumble more if the soapy water is sucked in
This is WAY SAFER that spraying combustible material, like ether, propane, or carb cleaner around, and worse case is that the engine is a little cleaner, lol, instead of on fire