I have a 2009 TL. It starts up fine. Revs fine. Then after 15 seconds it starts misfiring.
Turn the car off, restart it and the same thing happens. Runs fine, then misfires.
Shows P0302 and P0306. I replaced all 6 plugs and coils. Same exact thing happens.
I tried clearing the codes. Same thing happens and codes come back. Sometimes a P0304 is also there.
It's weird how it runs and revs totally fine the first 15 seconds of every start, but then starts noticeably missing after 15 seconds.
Any ideas? I am stumped!

 

Tell us the story, after what and when it started, did you do diagnostics by date, did you replace any sensors?
How much did you pay and where did you get the coils?

 

I bought it at the auction this way. They are cheap Amazon coils and plugs. I don’t think that’s the problem. Like I said, it runs perfectly fine for the first 15 seconds or so and then all of a sudden it starts missing. Every single time. It’s almost like something in the computer just goes crazy. I have not replaced any sensors. There is no error codes for anything like that. Just the two or three misfire codes that show up.

 

Then the first and most important thing is to put the original coils back in place. Throw the Amazon ones in the trash or give them to your enemy.
The problem could be in the MAF, EGR valve, EVAP purge valve, or bent valves.

 

It had the same exact problem with the original coils and spark plugs. I don’t think the coils and spark plugs are the issue. It runs totally fine the first 15 seconds. Every single time it is started. And every single time after approximately 15 seconds it starts missing.

 

Where did I mention the coil was the problem? The coil simply needs to be replaced with the original one.

 

Same problem after original coils put back.

 

Of course, it's the same problem, nothing should have changed, just keep those coils away unless you want to turn your car into a stationary cart. Now make sure the MAF is clean and OEM.

 

get a boroscope and put it down the spark plug holes, check the valves to ensure they are opening/closing properly. Also depending on mileage it could need a valve adjustment. Is it a FWD or AWD TL?

 

AWD. Someone else mentioned valve adjustment. But why would it be silky smooth the first 15 seconds or so every time???

 

I have a 2012 TL with 421,000 miles on the original engine. The valves have never been adjusted, and the engine runs smoothly. I know that in the CIS, we have poor gasoline quality and valve adjustments are recommended every 100,000 km. However, this can still cause the engine to run slightly unevenly, but I've never seen misfires due to poor valve clearances. Have you checked the MAF?

 

Do you actually hear it misfire and how does it drive after that ?
What are your fuel trims ? O2 sensors ? EGR ? maf and iat sensors ?
Have you tried doing a ecu reset and see if it goes away at least for a longer time ?
I suspect some pcm event is happening after it warms up like loop open/close or fuel trims going from idle/start level to normal operation level. After you have tried a full reset monitor via obd fuel trims, O2 sensors, EGR, IAT and MAF sensors see if they are reading normally.