I have a 2010 accent 1.6L It will run fine until I get a CEL... 1st it will flash, idle immediately is ruff, Code is p0300. The car will barley run like this, cant go over 25 mph. if I run it long enough I will start seeing P0301, p0302..ect. However if I clear the code... Instantly running normal again which might last 2 minute and might last 4 hour before it does it again.
I have:
check the timing belt
replaced the crank sensor (as a guess)
replace the plugs
check compression
leak down test
move injectors (move back since they are different colors)
swapped coils
vacuum test
propane test
replaced alt (unrelated code that I was getting)
watched live data on my snap-on scanner. The only thing I see as abnormal is the air intake temp ~120F which shows about the same time as the actual intake manifold and I am assuming its built into the MAP sensor. I wanted to watch the cam data but my scanner only says cam management active= yes and still says yes when the CEL comes on.
watch live data on the o2 sensor, purge system, injector pulse, voltage, ignition pulse, manifold pressures, throttle angle.... everything still seems to be reading but the car will barley run

The weird part is I cant seem to find anyone else who has this same issue. I also cant find anyone else that sees a "limp mode" in the accent other than the transmission's safe mode.

 

Can you post the actual data stream values ?

 

I am using a Snap-on Solus pro scanner which I'm not super familiar with the live data mostly shows yes/ no. However I go into the graphing section and it will show - - - - - - - - - - - for cycle 1 ignition cycle. It will show the 02 heater cycling as well as the 02 reading "lean/rich" . Shows timing adv = 5 deg, shows idle 720. exh temp 385, throttle angle = 0 .... these numbers dont really change when it starts running ruff. I can even drive down the road when the CEL is on and cant make it over 25mph, shows throttle angle 90 deg = wide open. The throttle body is also non DBW. The intake temp sensor is showing 125F but the air in the actual intake boot is 84F. I also don't see a separate sensor for it and the actual intake manifold is ~125F. So I'm assuming that its integrated into the MAP sensor. All these numbers were from memory but, Ill try to get you a lot better data this evening.

 

Hi Superman_006,
Well,,,,,,,,,,,,let's look a little more deeply into this.

What ever is causing the problem is easily reset by turning the key off and restarting the vehicle.
So,, what might cause this ? Not to po poo the scan tool or the user, but they haven't discovered the tool to think and chase down a problem, yet !
What I suspect might be taking place is a problem is showing up that the vehicle computer is sensing and to respond it is sending the system into LIMP mode.

Do you have and know how to use a multimeter?