2008 hhr rough idle only code is p0303 and it seems to come on mainly when running my ac. And that’s what when the rough idle and jumping is The worst. I’ve changed the plugs, coil, mass air flow sensor, fuel injector, evap canister, fuel pumps been replaced, gas tank dropped and cleaned. Idk what else to do to get rid of this cuz it didn’t do this one I’ll a few months ago and all the things I’ve listed have been done since then in effort to fix the problem. Some times it seems to help for a little while after certain repairs but it always Comes back.’my mechanic did a compression check and said it passed so it’s not mechanical. And again the only code that comes up is p0303 cylinder 3 misfire. Hopefully someone can help me figure this out. Thanks

 

What spark plugs did you install?

 

All of them

 

Ac Delco iridium

 

What number AC plug ?
"I’ve changed the plugs, coil, mass air flow sensor, fuel injector,"
I'm guessing you changed all the coils and all the injectors.
Or just the coil and injector for #3 cylinder.
How many miles on the car ?

 

Idk about the ac plug. But I changed all the plugs but only the coil for cylinder 3 and injector for cylinder 3 but I swapped them around to see if the misfire would move and it hasn’t.
But I’ve been noticing the last couple of days if I leave my ac off when I start the car and only turn on the air once it’s started so it just blows regular air not cold air. It seems to run a lot smoother and the check engine light doesn’t seem to come on. But if I start the car with the ac on and drive with it on the light comes on and the car jumps like crazy at stop lights When in gear and it’s started to jump while moving too now. It didn’t use to do that until the last week or two.

 

The car has about 240000 miles but the engine only has about 50000 it was new 2 1/2 year’s ago when I bought it and I barely drove the car until the last 6 months. And about a month into driving it for work it started having issues.

 

Logic says: if this only happens when the AC is on, maybe look at the AC compressor/clutch.

 

Check the coil wire harness, any rodent chew marks?

 

Well that’s what I’m hoping to get confirmation on is that the ac can cause a cylinder 3 misfire.
ive spent so much changing parts that apparently didn’t need changing and that’s a big one.
So I wanna be sure it could be the problem.
Cuz I see other posts That say it’s normal for that to jump a bit when the ac is running.
But it never jumped this bad before and it’s more than a bit, so I don’t think it’s normal.
Plus it’s something that’s gone away or calmed at times and then come back worse than ever the last couple of weeks.
And just the last couple of days I’ve been playing around with the ac idea.
But I actually feel like the car is just messing with me. Because it stops acting up for a while to make me think I’ve fixed it. Or stop acting up when I turn off the ac. But as soon as I tell someone I fixed it or I’ve narrowed it down it’ll start acting up without the ac or something. That’s kinda how it’s been the last few months and it’s driving me nuts with no idea what to do with this thing.