Check engine -p0303

Evening,

New member, short time lurker.

I just bought a new to me Taco. 2008 access cab 2.7 rwd with 189xxx miles.

I am getting the P0303 code as mentioned in the title. I have replaced the plugs and packs with Denso's. But, I still am getting a CEL and intermittent limp mode. I have not yet done a compression test. Is there anything that I missing (short of plug wires) that could be causing this? I am hoping against hope that it is not valve related.

 

Replace the valve cover (but more importantly the spark plug tube) gaskets and welcome to TW!

 

I had a P0303. My truck never went into limp mode but when I got the P0303 the truck ran like shit and was pumping smoke out the exhaust. I turned it off quickly. fired it up again and it was the same. I drove it down the block and quickly pulled over, killed the engine. Couple minutes later I started it again with no issue. That was stressful...

I replaced the spark plugs, It was at about the same milage. I only swapped the packs. still P0303 and eventually a P0420. I only ran good fuel. 87 octane, I used Mobile but any trusted name brand. I tried to use the same station consistently too. I did run a couple bottles of Lucas and a bottle of Duralast to try to deal with the P0420. P0303 never came back but the P0420 came back once a month for a year until I recently replaced the PCV Valve and hose.

Trucks never had that happen ever again and knock on wood my P0420 is gone now too. Trucks doing great now I hope that helps.

Good Luck!

 

If you didn't see any oil on the upper porcelain part of the plug, or the boot itself, replacing the valve cover gasket is not going to help.
The big 4 that cause a true misfire are; Fuel, Air, Compression, and Spark.