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2003 Pontiac Vibe runs rough, then improves

engine runs rough until 30 minutes of driving, then better. diagnostic shows cylinders 1 and 4 misfiring. Auto parts store guy suggested vacuum hose misrouted. New plugs less than a year ago.

What exactly were the codes? Have you swapped the coils from 1 and 4 with the coils from 2 and 3? If the misfire follows the coils, replace them. If the misfire is still on 1 and 4, pull all the plugs and run a compression test. I’d guess 1 and 4 will be low. Likely very low if the engine is cold. When it warms up the rings seal a bit better and the misfire goes away.

Sooo how many miles on the engine? Lemme guess, at least 150K? Is the check engine light on all the time?

Never, ever, get your diagnostic advice from the auto parts store guy.

I swapped #4&3, and 2&1. Diagnostic was the same. Pulled the plugs. Compression test reveals #4 185, #3 175, #2 185, #1 190. Engine warm.

I am assuming #4 is on my left facing the engine

Diagnostic codes are P0304 and P0301

Would have been nice to know all that from the start.

How many miles on the engine?

You might try a cold compression test and swap the spark plugs as well… new or do the 1-2 and 3-4 swap.

And #4 is on your right facing the engine. #1 is on the end with the serpentine belt