I've got two codes P0304 Misfire cylinder 4 and a P1121 Coolant control Valve position sensor stuck. Do you think these two are related? The car is running rough and has low power. I've been getting 35mpg for a while. I got some used injectors and a coil yesterday and plan on doing work tomorrow. The car has 355,000 miles on it. Still original injectors and coils.
Only relation is they're in the same vehicle. Try swapping, and check for oil on the plugs and cops. Has it been raining lately? Here is the work up for DTC P0304 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2054m/cip0300.pdf Here is the work up for DTC P1121 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2054m/cip1121a.pdf
I had a oily plug on the 4th cylinder picture is above. Where should I go from here? Valve cover gasket?
The tip of the plug looks dry, but the picture makes it hard to tell. If those happen to be the original plugs w/355k, replace them all. You may have a water leak in the spark plug wells, and or a valve cover leak, is the liquid on the socket greasy to the touch? Check the windshield cowling drainage holes, as that can be the cause for water intrusion. Clean the plug, clean the COP (coil over plug), and clean up the spark plug well before reinstalling the new/used plug. Does the engine oil on the dipstick have the same visual appearance as the liquid on the socket?
these are old but they aren't the originals. I think I changed them out at 250k with OEM plugs. The tip of the plug was dry. If it was a valve cover leak would all spark plugs look like that? The #4 was the only one. that is not what the oil on the dipstick looks like. The dipstick oil looks fine. The plug felt greasy. The coil was wet as well and kind of greasy.
Is that miles and not kilometers (no location in your profile), either way they should still have some life left. Not always, sometimes it can be a localized leak. You might try retorquing the existing gasket before replacing. Clean up the spark plug well and coil before installing the existing plug, then try to locate the potential water ingress point.
Put a new spark plug and salvaged coil in it. Runs fine. No misfire codes. I'll keep and eye on it next time it rains.
