I recently purchased a 2007 Saturn Ion 3 with 2.2 liter engine. It has 125K miles on it. After it gets warmed up the idle gets rough and the engine light flashes. The code reader says it’s a cylinder 3 misfire (P0303).

I replaced all four spark plugs and all four coils. It didn’t help. Any ideas?

Thanks

 

Update:

I just replaced the fuel injector for cylinder #3 with a brand new one. Same problem.

And the idle is rough. At a stop light I need to press on the accelerator a little bit to keep the engine from dying.

Should I do a compression test?

 

That would help the diagnosis. The injector driver in the pcm may be bad but please check all four cylinders.

 

Update:

So I replaced the plugs, coils, and the #3 fuel injector. No improvement.

And then it dawned on me that the problem started right after my son installed a new air filter. When he installed it, he disconnected the air intake hose from the air cleaner housing, and didn’t properly re-connect it – air was being suck in at the junction! So I properly secured the air intake hose to the air cleaner housing and the problem went away. Here is a pic:

https://www.dropbox.com/s/5pa1ozzdj6...20Ion.jpg?dl=0

Two lessons learned:

1. If an engine code appears, does it correlate with something you did to the car?
2. A code can steer you in the wrong direction. Just because a code says you have a misfire doesn’t necessarily mean there’s something wrong with the fuel or ignition system.

 

Very true, glad you solved the mystery. I work on a large utility fleet and I always ask “did you open the hood?”

 

False alarm. After the engine heated up, the problem came back... rough idle and cylinder #3 misfire.

Back to square one.

Any ideas?

Will be doing a compression check soon.

 

Make sure the plugs are capped correctly. Also make sure they're tight enough.

For chits and gigs clean your maf sensor and throttle body.

Also move the coil pack over to see if it follows the cylinder or not.

Last check the wiring for any corrosion.

All else fails bring it to me in east texas and ill give you a couple hundred for it. I need a base model to slap my extra blower kit on.

 

Nice to have you back.

 

Update:

I did a compression test. Results:

Cylinder #1: 178 lbs/in²
Cylinder #2: 174 lbs/in²
Cylinder #3: 60 lbs/in²
Cylinder #4: 178 lbs/in²

I then squirted some oil into Cylinder #3 and redid it:

Cylinder #3: 178 lbs/in²

From what I've read these results would indicate piston rings in cylinder #3 are bad.

BUT...

1) It doesn't burn oil.
2) There is no black smoke in the exhaust.
3) Every now and then there will be white smoke in the exhaust.

So is it possible the head is cracked, or the head gasket is bad, and the oil I added to cylinder #3 temporarily sealed it?

 

Way more likely that it has a bad piston and scored cylinder. The head is probably fine but it needs to come off to really investigate the cylinder. I would just install a different engine unless you feel qualified to repair it.