P0306 Misfire Rough Idle

[fdbyrne]

I would still be willing to bet it is the HG, even with the compression test passing.

Me too, unfortunately. A leakdown test would be more conclusive.

 

[O2VW1.8T]

If its a V6 with #6 misfire and mostly happens when it sits for a while then its the head gasket. Seen plenty and done a few, Spark plus i doubt it i've seen these with 260k on stock plugs and it still runs perfect which is crazy for a 30k plug.. Im a Toyota Master tech if it matters.

Testing compression wont matter it will read good, dont bother wasting your time, these engines are pretty much bullet proof besides the odd head gasket issues or the front covers leaking.. I own a V8 so i didnt have to deal with it if it happened:lmao:

 

[joshenator]

So leak down vs compression test. Is there a difference and if so which would be better for determining a HG failure?

 

[Brokeazzlos]

Do a leakdown test. That would be the best for diag headgasket

 

[run_on_four]

running rough after big dump

I have a 2000 4runner completely stock and today after going over a huge bump she cut out and rolled to a stop. I started her up again and she was misfiring and wouldn't go over 1500 rpm before cutting off. Barely limped it home. I'm used to working on older cars so i was thinkin' i could've thrown the timing off, i don't see a distributor so it's one of those electronic ignition deals... anyways could i have screwed up a few of the coils? or bashed a spark plug into disrepair? did I blow out the injectors? or maybe even conked out the sending unit/ fuel pump? has anyone else had this problem? PLEASE HELP!!!

 

[shahsmerdis]

If its a V6 with #6 misfire and mostly happens when it sits for a while then its the head gasket. Seen plenty and done a few, Spark plus i doubt it i've seen these with 260k on stock plugs and it still runs perfect which is crazy for a 30k plug.. Im a Toyota Master tech if it matters.

Testing compression wont matter it will read good, dont bother wasting your time, these engines are pretty much bullet proof besides the odd head gasket issues or the front covers leaking.. I own a V8 so i didnt have to deal with it if it happened:lmao:

oh nice info, I generally brush over V6 threads since I have a V8. but good to know.
yeah but you might need exhaust manifolds. might. i think these are two biggest issues of 4th gens of other wise two perfect engines. and it seems very small small chances, but sucks if you get them type thing.

 

[odie1]

Sorry for reviving an old thread, but I have a similar issue....with a twist....

Pretty much same as everyone else... except I have not detected any loss in coolant.... AND...

Wife started it yesterday... CEL comes on - rough idle... but did not stop after a few seconds like if normally does.. (when this occurs - which is not always).

She drives down the road half a mile.. stops (we live in the country), shuts the car off completely..... restarts... CEL is gone, and the engine runs as smooth as can be?

Anyone else had that occur ?

Thanks

Odie1

 

[odie1]

My apologies,

I should have added... Had the p0306 code (V6 engine) and I have very recently replaced the plugs, the #6 coil pack, and both down stream O2 sensors.... as mentioned on other threads..


Odie1

 

[kmmsmok33]

Update at almost 249k miles

Engine is still running well at 249K miles. Check light engine light came on again around 210K (in 2016) for same problem as stated coil #6. My engine thermometer gauge went red hot and was bouncing like crazy. For sure I thought my engine was done but it wasn't. I went home and poured about 1.5 gallons of pink coolant into the radiator and reservoir. Blasted my heater for ten minutes and engine thermometer gauge was back to normal.

I have never flushed my coolant since I've bought the car brand new. I've probably topped it off here and there but nothing like the 1.5 gallons. Since the last incident, I top off my coolant as needed every two to three months. Usually takes a quarter gallon to top it off. My car is almost at 249k.

I replaced all six spark plugs today after running them for almost 150k miles. All six plugs looked fine with no oil, just some rusts. Also changed all four rotors for the first time.

Other than regular oil changes every 5k miles, spark plugs changes, and brake replacements; I have been lucky and have not had any major issues with my car. Knock on wood again. My goal is to reach 300k miles.

 

[george65]

Misfire comes and goes

An old thread, I know. But, hopefully someone is still looking....

I have 2004 4runner 4.0 with a rough idle at start and a p306 code with a twist: it seems to come and go!

Several months ago, the vehicle started jerking and threw a p306 code. I changed the plugs and the coil over the # 6 cylinder. Problem solved...for about two weeks. Misfire happened again. Since I had read the threads about the head gasket, I took it to a highly rated garage and explained my concerns. They called back a few hours later and said, yep, head gasket. $4,200. I said no way and went to pick the vehicle up the next morning. It started great and the check engine light turned off! It also passed an emission test. So, I cleaned the MAF and Seafoamed it. Problem solved....for about 2 months. Now we are back to a slightly rough idle for a few seconds at start and it threw the p306 again just the other day.

Any ideas from anyone on this forum???? Before I drop a couple of grand on a head gasket, I would like an explanation of why it would come and go. Thanks in advance!

 

[george65]

Sorry for reviving an old thread, but I have a similar issue....with a twist....

Pretty much same as everyone else... except I have not detected any loss in coolant.... AND...

Wife started it yesterday... CEL comes on - rough idle... but did not stop after a few seconds like if normally does.. (when this occurs - which is not always).

She drives down the road half a mile.. stops (we live in the country), shuts the car off completely..... restarts... CEL is gone, and the engine runs as smooth as can be?

Anyone else had that occur ?

Thanks

Odie1

Did you ever figure this out? I have had something similar. Thanks

 

[aj1100]

Old thread I know. I'm desperate for some opinions.. I have 2008.with 180k Got oil change from dealer. 2 weeks later CEL, super rough idle, and dark smoke from exhaust and couldn't drive. No leaks. Towed to local shop and said P0303 and P0305. No decrease in coolant. They replaced plugs and coils but no improvement. They said they saw oil on the plugs and pbly something major. Towed back to dealer asking if their oil change caused any of it. They denied of course and said it has a blown head gasket and will be $8000+ to replace with used engine.
I have no idea where to go from here unfortunately. :...(
I'm in Charlotte area also. Any suggestions or ideas? Thanks in advance

 

[achang84]

i have the same issue with the fine / not fine P0306. I'll get the misfire, turn the car off, turn it back on, and then the misfire is gone. all within 5-10 seconds. Any explanation or remedy for this? I don't understand how a bad headgasket would sometimes be problematic and other times not? thanks for any help!

 

[YOKBB]

Have you checked your spark plugs? I got that code a few weeks ago, checked my plugs and the gaps were 2x wider than specs. I didn't really need to measure the gap, it was obvious the plugs were spent...

 

[325runner]

i have the same issue with the fine / not fine P0306. I'll get the misfire, turn the car off, turn it back on, and then the misfire is gone. all within 5-10 seconds. Any explanation or remedy for this? I don't understand how a bad headgasket would sometimes be problematic and other times not? thanks for any help!

The explanation...after the vehicle sits, coolant from the leaking head gasket gets into the number 6 cylinder. On 1st startup the engine misfires because the coolant will not let the spark plug fire until it clears that little but of coolant out of the cylinder...hence why it only lasts a few seconds (unless its so bad its straight dumping coolant). This is why it clears up after a few. Until you shut the vehicle off and the coolant continues to leak into the cylinder again

 

[Masdomonkey]

old post... I know that much but I also might have some insight if anyone is still having this issue.

04 1GR-FE
So three months ago I changed the head gaskets myself, only cost me 600$ including tools needed (valve compressor tool, compression tester kit) both heads resurfaced, New NGK iridium plugs and Denso coils, Head gasket Kit and water pump. Car was fixed no problems for three months.

Two weeks go Wifey told me it was running rough again but I ran my reader on it and it had p300, p304, p305 with no codes pending. So far I've cleaned the MAF and also the TB, replaced Fuel pump, replaced Bank1 A/F o2 sensor (didn't show voltage on my reader) compression checked #4 @147psi, Bought new plug for #4 (after I've replaced everything else lol). Last night I placed the new plug in and it ran a lot better than it did when the misfire was at its worst, after it got to temperature it ran good and misfired every so often at a redlight.

Im getting ahead of myself but I've noticed that after I cleaned the TB and MAF the idle was high on start up, I believe the computer isn't used too the airflow after I cleaned the carbon off of the TB so its over-compensating the A/F ratio...

So this had me thinking..

At a redlight it would skip but if I revved it to about 1,100 the mis would go away. On my reader it would show that my TPS% was at a base of 16.1%. So 1,100rpm was about 18.7% for me and had me thinking the computer can't adjust any lower unless maybe I reset it? Going to reset it tonight when I get home from work to see if it can re-learn past the misfire and maybe adjust it out.

Off topic but also good to note about your gauge cluster

This part is irrelevant but if anyone does their heads, make sure you re-attach the three ground wires on the back of the heads closest to the firewall, for the three months the car was good the gauge cluster was off. I had the one on the drivers side head (#2,#4,#6) not attached and found it last night after replacing Bank1 o2 A/F sensor. Ive looked around for a temp fix after I finished the heads and found myself on a Chevy forum and read that they have an issue with the silverados but a reach around was the OBDII reader staying plugged in but I didn't want to waste any extra volts to this. My Macgyver route was a paperclip in the OBDII port grounds, I just bridged them on the plug and it worked well. This is a temporary fix and I wouldn't suggest doing it unless you've smashed your hands enough times into the block tightening bolts and you're over it lol cause this can potently bend the tabs in the plug so your reader won't work and you will wish you had small fingers to fix the plug but if this happens to you after your heads, just be sure to check all grounds behind the motor.