I have an 05 MCS with no modifications. Bone stock engine wise. I keep getting a misfit cylinder 1 (P0301) code. The car idles great and even the misfire only happens under heavy acceleration and only intermittently. Here's what I have done so far.

New coil
New plug wires
New plugs

Issue still persisted so I did the following

Swapped injectors 1 and 3
Pulled and cleaned both MAP and TMAP sensors
Ran through a fuel systems cleaner
Fueled up ata different station (different brand also)

The issue still keeps coming up. Even with swapping the fuel injectors the code still specifies cylinder #1 as the culprit. The guys at the shop want to run a compression and leak down test, but wouldn't one of those issues cause a more consistent problem? I don't believe it's the fuel pump or filter as the car will run strong at high RPMs as well. Please help. I can't afford to get into a different car right now and can't afford for the shop to just run a bunch of tests trying to chase it down. This POS MCS has been to 3 different shops multiple times for the same issue and they can't seem to fix it. I desperately need help.

 

You need to have a compression and leak down test done. By doing the leak down test it will narrow down your issues. Normally with what you describe it will most likely be the valves. There are many posts on this issue.

 

Thank you for your quick reply. I've been looking at so many threads they have all started looking the same. Most of the threads seem to veer off topic quite bit. I will get the test done and see where to go from there.

 

Folks often toss lots of parts, hoping it will fix the issue.....but the head usually has to come off...

 

You are welcome.
+1 Take it to a shop and get the tests done before throwing anymore money at it like Zippy said.

 

Did a compression test and we should be good there. All the cylinders were within 2 lbs of each other. Would you still recommend doing a leak down test?

 

Yes. Here read this. http://www.wcengineering.com/articles/leakdown.html