Any older GM with a 350 would be preferential to this slow and painful torture. It took me a WHILE to read this thread. If the dealer can't fix it..............wtf? #TOHELLWITHALLSENSORS

So did you ever figure out the solution to your P0300 code ? I read through the entire thread and feel your pain tremendously. I currently am chasing down the same P0300 code you were, and have thrown or am about to throw all the same parts on my car to help trace said “misfire”. Would love to hear what solved it if fixed.

Nope! I was in a car accident back in July. I was forced to sell it because the guy that hit me wouldn’t admit fault. It’s literally that easy for your insurance not to pay for someone else’s damages. I took him to court and won. Anyway, don’t throw parts at your car. Take it to Nissan, Infiniti, or a Nissan specialist and have them run a thorough diagnostic before you start through it parts (make sure they check oil pressure). It’ll cost between $100-$200, but it’ll be much cheaper than replacing all camshaft and crankshaft sensors. My last diagnosis they couldn’t find anything. I did a compression test an all my cylinders were in spec. I didn’t do a leak down test. They shop wanted $500 to do a leak down test alone (I think they didn’t want to work on my car). After that I was gonna swap the ECU. I sold it for $900 and then bought an 2019 Audi A4. I’m done with car mods/repair outside of fluid changes and filter replacements. Hopefully in 8 years I can buy a stock new Porsche (whatever’s new) and get back into some speed under my feet again. Good luck with the P0300. I hope you figure out cheaper than $2000+ and hours/days I spent trying to.

So this is my experience with P0300.
Score card:
P0300 - 1
Me - 1
The first time it happened I was replacing the primary timing chain tensioner hoping to fix the start up rattle. I would bet most cases, like mine, this is not the tensioner/component causing the problem. When I pulled the bolts the engine turned and I jumped a tooth because I didn’t set the engine to TDC like a dumb***. Spent a few weeks telling myself everything was fine and it was a solenoid or something… I ended up swapping the engine because it had 296,000 miles on it and the timing chain kit costs as much as a used motor.
Second time:
The new to me engine came with what look like brand new coil packs and spark plugs. After the initial hey it’s got new coil packs wore off, I started to wonder why does it have new coil packs. I think I know the answer now…
The valve covers leaked on the newly wrapped headers so I had to replace the gaskets and while I was in there I noticed the fuel injectors looked pretty old. I figured I’d change them out later when I install the plenum spacer and didn’t really give them too much thought.

Finally I got everything back together and running. While we’re topping up the transmission with fluid (also replaced because “while it’s out”) I hit the idle air relearn procedure on the scan tool. The engine started missing like a ****… cylinder 4 wasn’t firing at all. I figured this out with the tool and the cylinder check feature. After about 10 mins the SES light came on with P0300….
Tinkered with it for a few mins and gave up for the day…
Got back home and started looking to see if anyone has had anything like this happen to them and came across this post… It didn’t make me feel any better about the situation.
Some more history:
Replacing valve cover gaskets on the old motor, I broke a bolt in the intake for the lower plenum. At the same time i installed the plenum spacer (just left the broke bolt because it was in the middle and I didn’t want to deal with it.) So the intake and plenum had a leak, but it was a small leak.

So, this morning I go over to swap out the injectors and check the spark plug (already checked coil pack.) Got the fuel rail out of both engines and start looking at the intake. I suspect if the fuel injectors are original so is the intake manifold gasket. Run to autozone and grab new gasket for the intake (“while I’m in there”) and get to thinking. What if the ecu still programmed for the old motor was running fine because of the leak on the old motor and when I hit relearn the manifold gasket is leaking and the ecu can’t adjust for it (also had the oil cap gasket trapped in the plenum).

I’m not sure if it was disconnecting the battery over night, the fuel injectors and fuel rail, the harness to the fuel injectors, the trapped rubber oil cap gasket thing, the intake manifold gasket, or the loose cold air intake tube couplings, but when i fired it up today there was no miss and the code was gone.
Hope this helps someone else.

Sorry for the late reply. This is dated from May 23 and I got it Oct. 1st, so... Anyway, I have had a couple of sidelining health issues that have put me waaay behind which makes chasing down BS through an electronic jungle that much more annoying (have I mentioned that I'm sick of the new stuff?) I have narrowed down the pulsing idle to (as I recall) the variable timing "things" (VVT?) One on each side toward the front of the engine. They are easily removed and cleaned. They have internal screens that must be cleaned (Utube is your friend) and they're easily tested. I'm going to change the oil before the test firing. I also get to fix a heater hose that blew as a result of the increase in pressure from the pulsing idle as well as replace and clean up where the coolant spewed in the engine bay. Oh, and added bonus, it has a moon roof and their lamely designed drains clogged up causing mold in the car (there is a Utube on how to replumb that crap too. Ahhh, good times. Man, I have been around a while and owned all kinds of cars. The worst was an old AMC Rambler and it was a champ compared to this garbage. Isn't "advanced technology" wonderful? The K.I.S.S principle will always rule. If I ever get this dumpster fire fixed, I will find it a new home. Good luck my friend. Let me know how it goes.