Intermittent misfire all cylinders at idle

[bzettler83]

2005 V8 170k miles.....

Yesterday it was pretty hot here in a/c and of course I get a Flashing Check Engine Light and of course all the other lights that come along with it.

Get home and pull the codes. P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308. So basically misfire in all cylinders.

What is interesting is that this only happens at idle. If you bring the RPM up to 2k the light shuts off and everything is back to normal. Doesn't smoke, run rough, no other signs of an issue. Did a quick spot check and all lines seems to be connected, I dont see anything obvious.

What should I be looking for?

 

[lightfreak]

Just throwing out some ideas:
Could be bad gas , try filling up with premium and see how it reacts.

If it’s been a while change out the plugs make sure it’s same heat range as OEM plugs. You can try cleaning the MAF sensor and throttle body while you’re at it.

It’s not likely all coils would go bad at the same time so that leads to internal timing problems being possible culprit. Water pump leaking onto the belt can cause it to stretch. Failed tensioner or just old belt with one foot in the grave.

I did read a similar issue on here caused by aftermarket upstream 02 sensors , but he had rough idle as well.

Good luck and do update if you find the solution.

 

[bzettler83]

Serpentine belt and timing belt were done at around 100k with water pump, everything looks good there. I dont drive it much recently, I will fill up with good gas, clean things up a little, and see if we have any success. Thank you.

 

[Bossman]

http://www.toyota-4runner.org/4th-gen-t4rs/147831-v8-misfire-idle.html

http://www.toyota-4runner.org/4th-g...8-rough-idle-misfiring-p0300-p0301-p0308.html

http://www.toyota-4runner.org/4th-gen-t4rs/239618-4-7-v8-misfire-condition.html

 

[rwrobs777]

Hi !!
Gen 5 owner here and engine diagnostic hobbyist. So it just misfires at idle ??...The first thing I'll do is hold up a piece of paper or a dollar bill up to your tailpipe...does the bill get drawn into the tailpipe at idle when you are getting the misfire ??...if so, YES
it's a misfire. You just have a code reader or a decent scan tool ??...first thing I'm thinking is vacuum leak because a car runs better at higher RPM but to know for sure I'd have to look at your fuel trims...I'm lucky enough to have a few scan tools, oscilloscope to check ignition systems, and a smoke machine and a lot of other diagnostic equipment so it's a little easier for me to diagnose with this equipment. Without a scan tool to look at O2 sensors and fuel trims it's a little tough for the average DIY'er. MAKE SURE YOUR TANK HAS MORE THAN 1/4 TANK OF FUEL BECAUSE IF YOU'RE RUNNING ON FUMES THIS CAN CAUSE A MISFIRE !!.... a bad pulley can cause a misfire...ANYTHING that causes the crankshaft to slow down will cause a misfire...try looking for a vacuum leak first...spray some Brake Kleen around the intake manifold and all vacuum lines and see if the can runs different !!

 

[bzettler83]

Hi !!
Gen 5 owner here and engine diagnostic hobbyist. So it just misfires at idle ??...The first thing I'll do is hold up a piece of paper or a dollar bill up to your tailpipe...does the bill get drawn into the tailpipe at idle when you are getting the misfire ??...if so, YES
it's a misfire. You just have a code reader or a decent scan tool ??...first thing I'm thinking is vacuum leak because a car runs better at higher RPM but to know for sure I'd have to look at your fuel trims...I'm lucky enough to have a few scan tools, oscilloscope to check ignition systems, and a smoke machine and a lot of other diagnostic equipment so it's a little easier for me to diagnose with this equipment. Without a scan tool to look at O2 sensors and fuel trims it's a little tough for the average DIY'er. MAKE SURE YOUR TANK HAS MORE THAN 1/4 TANK OF FUEL BECAUSE IF YOU'RE RUNNING ON FUMES THIS CAN CAUSE A MISFIRE !!.... a bad pulley can cause a misfire...ANYTHING that causes the crankshaft to slow down will cause a misfire...try looking for a vacuum leak first...spray some Brake Kleen around the intake manifold and all vacuum lines and see if the can runs different !!

I have a scan tool but I cannot measure fuel pressure and that was an initial instinct. I am going to work on it this weekend and go from there. I am planning on putting some more gas in it, pull my intake apart and clean everything and go from there.

My scan tool does measure vacuum pressure, is there a bench mark PSI I should be looking for?

 

[rwrobs777]

It wouldn't be fuel pressure because you have no misfire under load...if the misfire WAS under load we can maybe assume that the fuel pump output is low and you'd get a lean misfire...why are you pulling the intake off ??...use the brake kleen first and if idle changes while spraying it around any vacuum lines you've found the leak...do you have any vibration in the truck out of the ordinary ??...frozen u joints or driveline imbalance can cause random misfire. Does your scan tool read fuel trims ??...it's one of the most important thing for me to diagnose misfires. If you tool has it look at your STFT (short term fuel trims) and LTFT (long term fuel trims)...if the LTFT are over +10% you have a lean condition...read both fuel trims at idle and raise the RPM to 2500-300 RPM...if those fuel trim numbers start to decrease you have a vacuum leak...this is the easiest check for a vacuum leak. Your scan tool probably read BARO and not engine vacuum...engine vacuum is normally 18-22 inches Hg. If your scan tool can read your O2 sensor PIDS let me know that also !!...misfires can be hard to diagnose !!

p.s. Try the dollar bill trick at idle and let me know if it's misfiring !!

 

[bzettler83]

It wouldn't be fuel pressure because you have no misfire under load...if the misfire WAS under load we can maybe assume that the fuel pump output is low and you'd get a lean misfire...why are you pulling the intake off ??...use the brake kleen first and if idle changes while spraying it around any vacuum lines you've found the leak...do you have any vibration in the truck out of the ordinary ??...frozen u joints or driveline imbalance can cause random misfire. Does your scan tool read fuel trims ??...it's one of the most important thing for me to diagnose misfires. If you tool has it look at your STFT (short term fuel trims) and LTFT (long term fuel trims)...if the LTFT are over +10% you have a lean condition...read both fuel trims at idle and raise the RPM to 2500-300 RPM...if those fuel trim numbers start to decrease you have a vacuum leak...this is the easiest check for a vacuum leak. Your scan tool probably read BARO and not engine vacuum...engine vacuum is normally 18-22 inches Hg. If your scan tool can read your O2 sensor PIDS let me know that also !!...misfires can be hard to diagnose !!

p.s. Try the dollar bill trick at idle and let me know if it's misfiring !!

I have LTFT1 and LTFT 2 as well as STFT2. So I will check that and do the dollar bill trick.

 

[rwrobs777]

You should have STFT 1 also....let me know what your long terms are reading at idle...if they are higher than 10%...if it's less it won't set those DTC's. anything around 23-25% will set a lean DTC...You probably have an intake leak...Like I said rev the engine to 2500-3000 and see if long and short terms decrease...if so it's a vacuum leak. Good Luck !!

 

[IRQvet101st]

You should have STFT 1 also....let me know what your long terms are reading at idle...if they are higher than 10%...if it's less it won't set those DTC's. anything around 23-25% will set a lean DTC...You probably have an intake leak...Like I said rev the engine to 2500-3000 and see if long and short terms decrease...if so it's a vacuum leak. Good Luck !!

Ok so I know this is an old thread but figured I'd try for some help. I have the same issue as OP, my ltft and stft are around 1-3% at 2k rpm they drop below zero. Vacuum leak?