Had a customer's old truck that was running rough, turned out to be a cracked vacuum line behind the intake

This was on a '92 F-150 that came in last Tuesday. The guy said it had a bad idle and would sometimes stall at lights. I started with the usual stuff, plugs, wires, fuel filter, but nothing fixed it. I was about to call it a day when I decided to just spray some carb cleaner around the base of the intake while it was running. The engine speed jumped up right behind the throttle body, and sure enough, there was a tiny crack in a vacuum line I couldn't even see without a mirror. It was maybe an inch long, tucked way back there. Replaced that one piece of hose for about two bucks and the truck ran smooth as glass. It's crazy how such a small, cheap thing can cause such a big headache. Anyone else have a story about a simple vacuum leak that took forever to find?

2 comments

2 Comments

emery_craig16d ago

Man, I used to think vacuum leaks were only a big deal on older cars with all that spaghetti under the hood... but my buddy's 2010 Civic had a rough idle that drove us nuts for a weekend. We replaced the PCV valve, cleaned the throttle body, the whole deal. Finally found a tiny, dry-rotted elbow on a brake booster line that you couldn't even see without taking the battery out. Such a dumb little piece of rubber. It's wild how a system that just moves air can cause so many problems.

the_kevin15d ago

You're right, @emery_craig, but that brake booster line is a huge vacuum leak source, it's not just moving air, it's messing with the engine's whole air/fuel mix.