05' GSR with Exede, and Bushur TB. Car misfires/stutters (must let off gas to get it to run smooth) all the time. Check engine light and a code reader (Advanced Auto Parts) says I have a PO300 (random cylinder misfire).

Guy at Advanced Auto says I should replace the Coils. Do you guys agree? What else should I do?

 

There's a flash from the dealership to fix your problem. I don't know how that will conflict with your xede though.

 

Do a search for PO300....you'll find that it is a common issue and not really something that hurts perfomance from what I understand once the code is thrown and you're past the car stuttering. Replacing the coils is NOT the answer.

 

First question would be what weather the car was tuned in...is the weather colder now than it was when you were tuned? If so, could be running lean, which will throw a p0300 code as well. Otherwise, I would check the plugs...not sure how long its been since you have replaced those.

 

my 03 VIII GSR threw it too when i was going steady down the freeway at speeds over 160 (+20)

but 2 days later the engine light whent out and and checked and the code was gone???

 

Have had this set up for 2.5 years and no problems until now. Nothing changed. Car only has 30k miles so a change in plugs does not seem necessary. Pulled two anyway and they look fine. But, I'll change the plugs and try different gas/station to see if this helps.???????????

 

Why spend money beating a dead horse.....a search is free. Like I've already said, do a search for the PO300 code and you'll quickly find that it is common to Evo's and really a false reading....it's the code that seems to trigger a misfire (the sputtering), not the misfire triggering a code. Doe a little research before blindly wasting money hoping you solve the problem.

 

30K, i would get new plugs if I were you.

 

it's probably the plugs? When was the last time you changed them, if ever?

 

I didn't notice 30k with no change of the plugs. I would definetely change the plugs, but don't expect that to be the fix for PO300.

 

Yeah you really don't need to replace coils. The P0300 code on VIII isn't a true code, but the ECU think it is a misfire because of some sort of harmonisation from the transmission inducing fake "knock"(I'm going from memory, so don't quote me on that). There should be a dealer fix as there was a TSB issued. Spark plugs, ehh possibly. Could even be your gapping. It would be a good idea to go ahead and replace your plugs to eliminate that possibility. You'll need to sooner or later, right?

Go ask your dealer about the TSB. You have mods on the car, so this might be a little trickier to get the flash and keep your warranty.

 

I have done a thorough search on this forum and unfortunately no one seems to have found a solution to the PO300 problem although most are highly modified Evo's. No one has described the symptoms I have and found/stated a specific solution. I really don't want to go to the dealer at this point until I try some inexpensive solutions on my own.

I did a google search and actually came up with useful information indicating that this code can come from a variety of conditions relating to spark and fuel (lean condition); bad plugs, bad coil(s), bad O2 sensor, vacum leak, Egr valve, bad cam position sensor, clogged or bad injectors, bad gas, clogged fuel filter, bad fuel pressure regulator or bad plug wires.

Thanks to some of your input I am going to try to replace the following items in the order written and hope that I don't get too far down the list to aleviate the problem: new tank of gas, fuel injector cleaner, plugs, fuel filter, O2 sensor, EGR valve.

If this does not work I will go to the dealer to see if the coils are faulty ($385 each times 2) or if there is a vacumm leak. They can test these, I can't.

 

Replace your plugs every 3-5000 miles.

 

have you tried the creader fix? you keep a creader attached and it keeps the code cleared. the lack of code keeps you from actually misfiring.


and do yourself a favor and don't take advice from the guys at autoadvance...

 

You can get the p0300 from running lean at cruise. Alot of people including myself when messing with the open loop , having the a/f too lean causes misfires and that code. But, i'm pretty sure it's ignition based.
Plugs should have been changed at 25k even if they looked good.

You can run the stock plugs again or try coppers(require changing every oil change) Also like someone mentioned, you could also try a smaller gap.