Overheard a guy at the parts counter say most people replace the wrong sensor first

Was waiting for a serpentine belt at O'Reilly's in Phoenix and this old mechanic told the guy behind me that 90% of check engine light diag starts with swapping a MAF when it's usually a vacuum leak. Made me think about all the times I threw parts at a problem without checking the simple stuff first. Now I grab a can of brake clean and hunt for leaks before I touch the wallet. Anyone else got a go-to trick for finding vacuum leaks quick?

2 comments

2 Comments

sethc1213h ago

Man that part about throwing parts at a problem hits CLOSE to home. Did the exact same thing with my old F150 - swapped the O2 sensor AND the MAF before my neighbor came over and found a cracked vacuum line right behind the throttle body with a cigarette lighter. Now I keep a cheap propane torch unlit in the toolbox, run it along the hoses while the engine idles, and listen for the rev change. Works way better than brake clean and doesn't stink up the whole garage.

charlesj469h ago

Propane trick is solid, I've done the same thing on a few cars and it never fails to find those sneaky little leaks. Just gotta be careful around any hot manifolds or spark plug wires though, had a buddy learn that the hard way with a minor scorch mark. One thing I'd add is if the idle doesn't change much with the propane, try spraying a bit of carb cleaner around the injector seals too, sometimes those plastic spacers get brittle and suck air without a visible crack.