Hey guys, got an issue that is causing me some grief with my R50. Bought the car in 2011 with 33K miles on it. It ran pretty reliably until the end of 2017 when it overheated due to a failed alternator (and subsequently cooling fan). Got that fixed and everything seemed to be going well for a while when it started idling rough. Did some diagnosis and it turned out to be a burned exhaust valve. Over the course of the summer of 2018, the car had clutch issues, followed by trans issues, which were resolved by swapping the 5 speed for a 6 speed. I also got a cylinder head from a Pull-A-Part yard, had it rebuilt and swapped it in October to fix the exhaust valve issue. During that time, the car would throw the occasional code but with all the other issues, I just cleared it and kept going (driving and repairs). After the cylinder head swap, I thought I had it all buttoned up. The car runs like a sewing machine. I average 29mpg for my commute (up from 23 with the bad valves) and seems to have good power. My issue comes from the occasional P0300 code that gets thrown periodically. The car will start missing, light up the light, and then clear up moments later. This happened prior to the head swap but I attributed it to the cylinder head.

It also happened to me today on my way to work. It started missing about 2 miles from my exit. I continued to my exit, and when I pulled off the ramp and into work (about 3 miles total), it cleared up and was idling fine. I drove the car to lunch and aside from clearing the code, there were no indications of any issues.

What I have done, aside from swapping cylinder head and associated gaskets, are the plugs, wires (about 6 months previously), and coil pack. Since I can't seem to catch it when I have a scanner with me, I can't see what my fuel trims are to see if it is a lean condition.

I get no other codes, just P0300. When this happens to my wife, she shuts the car off, lets it sit for a few minutes, and it'll drive fine afterwards. And this only seems to pop up once every month or two.

Any suggestions as to what to check next? I'll buy whatever part fixes it, I just don't want to constantly throw money at it. Oh, current mileage is 141K.

Thanks all.

 

Presuming its missing at highway speed as opposed to idle. If so,air filter, fuel filter, fuel injector cleaner, cleaning throttle body and connections at the coil are where I would start. Cheapest , easiest first. That code is generic misfire, not a specific cylinder. Redline SI-1 is pretty good stuff, dump a bottle in at normal fill up time. If dirty injectors were the problem, you will know if this worked after another couple fillups.
good luck
Bruce

 

Well, to wrap up this thread. The issue with my P0300 turned out to be an issue with my 6-speed swap and the bad DMF flywheel. The flywheel was part of the swap when I converted to the 6-speed and I guess it was bad right out of the gate. The engagement of the DMF is very smooth and it drove great, initially. Once I narrowed it down to the flywheel I was able to hear a slight knocking it was making when the pedal was out and would quiet down when the pedal was pressed. When I removed the flywheel, I did the LUK test and it had nearly 10 teeth of movement with just my hands when it should've only had 3-4. My guess as to what happened is that there was enough slop in the flywheel that when the vehicle was moving at highway speed but at light throttle openings, the weighted part of the flywheel was bouncing between the springs and the computer was picking up that bounce and reporting it back as a misfire. Now that I'm running a valeo SMF it has been driving beautifully. I'm glad to have my car back and be able to trust it on a road trip.