I recently acquired a 2010 California in an auction that has around 30k miles. It has a recurring misfire on cylinder 1 when under load and at around 5-6k RPM. It seems to run great otherwise, but if I accelerate hard I can sometimes feel a slight hesitation with an audible sputter in the higher RPM range just before the CEL comes on with an engine control system error message. It throws a P0301 code. It seems to accelerate just fine until it hits that RPM range. The problem is recurring, but it only happens about half of the time under those conditions. Some drives are perfectly fine, but when it starts to misfire it will usually continue to misfire consistently under those conditions thereafter. I don't have any service records for the vehicle. The oil was dirty when I bought it and it had the wrong oil filter installed. (I think it may have had a filter for a 360 installed?) I reset the service indicator after changing the oil, oil filter, air filters and transmission fluid. The service indicator was last reset in 2018, so it may have been a couple of years. One other things to note is that the engine oil has a slight fuel smell to it. My understanding that that oil dilution can be an issue with GDI engines, especially if there are misfires, but I have not smelled enough oil to know what is uncommon. Maybe that is just a symptom of the misfiring and not indicative of another problem, but I am not sure at this point. Changing the plugs and coils had no improvement. I pulled the injectors and had them tested and cleaned. Some of the injectors were very restricted and/or leaking, but all are good following cleaning. However, cleaning the injectors did not resolve the issue. I have not performed a compression or leak down test yet. I need to find a better 10mm adapter for my compression tester that will actually fit into the sockets. Also, is there procedure for disabling the injection and ignition while doing a compression test for these cars? Do I need to pull some fuses or relays unless I have access to a DEIS tester? I do not think I could do that with my Launch x431 pro. (I can manually actuate each of the injectors using it, which is how I dropped the pressure in the fuel rails before removal.) The Launch provides some access to the various systems and live data on the California, but I am not an expert on modern engines and need to do some more research on what might be out of spec regarding the available data such as ignition advance, etc. When I had the intake manifold off to replace the injectors, I noticed that the intake ports in the engine seemed pretty dirty. They looked like they had a good coating of oily sludge. I probably should have taken the time to clean them out before reinstalling the intake manifold, but at that point I assumed the problem was one of the severely restricted injectors that had been operating at less than 50% capacity. If one of the intake valves is fouled, could that cause a misfire only at high RPM? I have also been suspecting that there could be an issue with one of the variable timing solenoids for bank 1. I have read that the VVT kicks on to adjust the timing when under load at higher RPMs, which would be consistent with when I experience the misfiring. If a VVT solenoid is malfunctioning, could that cause a recurring misfire code for a single cylinder without additional DTC codes? The code is always for a misfire on cylinder 1. I would think that a VVT issue would affect all of the cylinders in that bank, but I assume the ECU takes over with the malfunction is detected. I noticed there is probably a slight oil leak somewhere around those solenoids on the right bank, which is where the problem is. No oil is visibly leaking or dripping, but the tops of the solenoids, the gasket around them and the valve cover at and below the gasket is dirty which seems to indicate a slight leak. I am not experiencing any rattling upon start up, so hopefully the variators on the cams are still okay. My understanding is that the VVT solenoids used in the F136 engines sometimes fail from high pressure oil leaching up into the coil and connectors. The dielectric grease around the electrical connectors is brown and gummy. The workshop manual says to try applying UNIFLOR 8917 grease to the connectors before replacing the control solenoids. (That particular grease is available online for the reasonable price of $600 for a 14g jar.) Any reason why I couldn't use some other kind of high-temp dielectric grease used for spark plugs? I assume there are issues with the electrical connectors? I am going to try to testing the actuation of the VVT solenoids using a 12v battery, test for shorts and see if there is any difference between them in coil resistance. That might confirm a likely problem, but it might not rule out a mechanical failure in the solenoid valves. Has anyone had a similar problem? Anything I should look for in live data streams that could be useful? Anything related to timing or fuel trims that could be helpful?