P0300 - 98 4Runner (1 Viewer)

[shack]

I am posting this for a buddy of mine who recently pulled this code on his truck. He has 103k on it and is running the orig timing belt.

P0300 - Random Misfire.

According to the manual this code could be an issue with any of the following.

He has already cleaned the MAF. Plugs and wires are 2-3 years old.

Anyone have experience with this code on this year truck? A mud search proved to me that it is common across all of our trucks. At the very least I would like to put the "Trouble Area" items below in a priority order for diagnosing. Any help would be appreciated!

 

[shack]

To add to this....

This is the only code he pulls.
It is intermitent
RPM's bounce at idle +/- 400
Happens under load and idle

 

[Duane]

well interesting that you can see/feel the rpm surging
When my MAF got dirty enough it set a too lean code I think it was.
I would check the plugs, make sure they are the dual tip Denso units as using singles has caused problems. at minimal as found plug conditions might point to a given cylinder or something wrong looking.
Same tank of fuel as this symptom showed up on or on multiple tanks?

for me I would check first... plugs, wires, coils. I would put a timing light on it to see if it is moving around.

 

[gnu333]

Thought it'd be easier if I just joined so that I can clarify.
On the way home from a 300 mile trip I start to get some sputtering and misfires only under load. The truck is shaking and gasps and bounces when I accelerate. This continues to happen off and on for the duration of the trip. The CEL flashed on and off once or twice, but never stayed on for more then 5 seconds. Next day I took it to my neighbors shop and he said the only code was P0300. I replaced the plugs and wires 2/3 years ago with OE from the dealer. We pulled a couple plugs and they looked fine. The MAF sensor had never been cleaned and was due, so we cleaned that. Ride home was fine, but the next day it started happening again. This time even at a standstill at idle the rpm's are bouncing +/- 200 and the truck is nearly bouncing. Took it back to him and there were no new codes. I am out of town on travel a lot lately and don't have the time/money to throw parts at it. I just find it odd that no specific cylinders triggered a code. The problem is definitely intermittent as I drove it the last 3 days with no issues. Any help is appreciated.

Same tank of fuel, last filled at a small town station off the interstate. Haven't checked coils yet cause I thought that would have given me a specific cylinder misfire.

'98 3.4L 4Runner, 130k miles
original timing belt and water pump
newish (2-3 yrs) belts, plugs and wires
thanks

 

[Duane]

Well it seems odd that not a single cylinder misfire code comes up but my problem recently with the crank gear and key coming loose made no sense to set the P0300,302 and 305 codes either.

If you own a timing light I would do that next time myself. See where the timing is at and if it is moving at a constant engine speed.
Also can clamp it on 3 different spark plug leads and see if the pulses are consistant. Might seem weird with the double pulse from the waste spark setup but look for consistant flashes.

Could also be a crank sensor or cam sensor possibly failing or loose. Or maybe that crank pulley is getting sloppy but I think it is characterized by the 3 codes I had.
The flashing CEL was explained to me as excessive unburned fuel hitting the converter so not a scenario you want to be running in for a long time either. I would back off my throttle and it would quit flashing. Mine never jerked really it was just off /wandering on timing and likely not knowing when to inject the fuel.

Check for a good ground connection too.