Intermittent misfire and stalling; no CEL

[87warrior]

1999 with 287K miles.

My cruiser has developed what I believe is an intermittent misfire. It ‘feels’ the same as a bad coil pack misfire, but it is intermittent at best and does not trigger a Check Engine Light.

The Cruiser has also stalled twice since this has started-
1) Coming to a stop on the deceleration ramp after exiting the Interstate
2) Turing into my driveway after decelerating from 55mph on the county road

I’ve used the Torque App to scan for codes and there are no codes ‘pending’ either.

I’ve been monitoring the long term fuel trim of each bank to try and determine where this issue may be, but unlike the typical bad coil misfire, the fuel trims stay steady. In addition to the fuel trim I am watching the MAF/IAT sensor, coolant temp, timing, throttle position and voltage. None appear to flutter, or falter when this misfire occurs. The misfire has not occurred with a heavy foot. It seems to occur with minimal throttle input (flat stretch on 2 lane highway or gentle slope downhill).

I did replace the alternator a few weeks ago. The job was simple and straight forward. I did verify everything I touched during that process was where it should be.
Fuel filter was replaced with a Toyota filter last summer.
MAF was replaced with Toyota sensor last summer.
2 new Denso coil packs on bank 1 last summer (Bank1 has 4 new coils in the last year, bank2 still sporting OE).
New Iridium plugs last summer.
Perhaps coincidence, but the outside air temperature has been below 10 degrees since this issue started.

I am not sure what to check next. I do have TechStream on a laptop I could run, but I am not convinced it would illuminate anything for me or would I know what to look for. The Bank2 coils are suspect and I do plan to replace them for good measure, even through nothing is pointing at them (expect for age).

 

[re_guderian]

These types of things are frustrating to diagnose. Here's my experience. Not saying yours is the same, but hey, it's one more thing to check... Good luck!

Intermittent stumble/miss/misfire on 2000 LC - no codes

 

[87warrior]

@re_guderian - Thanks for the idea. I certainly will not dismiss that as a possibility... will check!

The frustrating part is, while the Cruiser is causing problems my old TBI 4cylinder Jeep fired up and ran to town with no issue after sitting in the cold for two weeks

 

[2001LC]

I read your threat linked above @re_guderian. Interesting you found loose spark plugs. I've been find a lot of them loose, with numbers 3, 5, 4 & 6 loose the most often. I've even found factory installed plugs under 60K miles loose. It may be Toyota 13ft-lbf torque is just a bit to light.

@87warrior I'd check all vacuum lines as well. They get even looser in the cold. Two sets most overlooked are on the two on VANE pump (power steering pump) and both PCV hoses & the grommet. If yours are factories, they'll need replace. In fact you should be on about third set by now.

If rigs sits a week or two at a time, gas may have moisture that's freezing up. I've had a lot of fuel related issue lately. Some 44K or tectron can't hurt.

Hook up techstream and check for pending, is not a bad next step. I just saw one that seemed cold was affecting Magnetic Clutch Circuit of throttle body (P1126 pending)

Make sure to check all your grounds, recheck alternator connection, MAF, battery clamps and air box for looseness. Last job is always first suspect.

 

[87warrior]

A brief update.

I used Tech Stream to see if it could find any pending codes related to a misfire. It reported no codes, active or pending.

I installed 4 new Denso coils on Bank 2. I believe the coil for cylinder #4 was causing the issues. The coil was wet in the spark plug cavity with what looked like extreme condensation. The coil on cylinder #8 also had some moisture on it. All spark plugs were tight on Bank 2.

I found no moisture on the Bank 1 coils (all new Denso within the last year) and the spark plugs were tight.

I have driven it twice with the new coils and it has not had a misfire or stumble of any kind. Ambient air temperature has warmed up 15 degrees. I found nothing out of sorts with my previous alternator work.

What I'd like to know is how so much moisture could get into the spark plug valley and on the coil. I've done no engine washing or shallow water crossings since October.

 

[abuck99]

Do you drive a lot of short trips and the truck sits alot? Sparkplug seals in the valve cover leaking maybe? If you are driving short distances, moisture in your crankcase oil doesnt have an opprtunity to burn iff and might be discharging vapor through the worn seals and condensing in that area. Just a guess.

 

[KillerBox]

Subscribed because I am chasing down a stalling problem too. If I find out anything, I will definitely let you know.

My guess on my stalling is leaning towards my alternator wiring because I just replaced my alternator too. At idle sometimes, the lights blink lightly but, goes away as soon as I idle more than 900 RPMs. But, I haven't found my definite problem.

 

[87warrior]

Do you drive a lot of short trips and the truck sits alot? Sparkplug seals in the valve cover leaking maybe? If you are driving short distances, moisture in your crankcase oil doesnt have an opprtunity to burn iff and might be discharging vapor through the worn seals and condensing in that area. Just a guess.

I average 2-300 miles per week. The 100 is my daily driver and does at least 15 miles one way at 55mph everyday. I'm also on the road a lot throughout the day.

Since the coil packs are easy enough to remove, I am going to make inspecting them for moisture at oil changes routine. I need to determine a pattern, if any, to figure out why/how they are getting wet.

Subscribed because I am chasing down a stalling problem too. If I find out anything, I will definitely let you know.

My guess on my stalling is leaning towards my alternator wiring because I just replaced my alternator too. At idle sometimes, the lights blink lightly but, goes away as soon as I idle more than 900 RPMs. But, I haven't found my definite problem.

The Cruiser seemed to run fine with a shot alternator before I replaced it. The alternator died on my way to work and on my return trip home my battery voltage dropped to 10.2v (per Torque) yet the cruiser was running fine. I immediately put the battery on a maintainer and it seems to have survived the drain.

 

[camino70]

I've felt the stumble before without a CEL. On two different occasions it took about 200 miles before anything showed up pulling codes.

 

[2001LC]

I've not seen water in spark plug tube(s). Except from outside source, which washing or water crossing certainly qualifies. Missing undershielding or wheel well shielding could allow excessive road water in engine compartment.

Did changing coils fix the issue?

 

[87warrior]

I have not had a stumble, stall or misfire since installing 4 new coils on bank 2.

I am hesitant to say the issue is fixed since the misfire occurred with the ambient air temperature around 5-10 degrees and the current air temperature is 55 degrees. We are forecasted to cool down significantly this weekend so I should be able to see if the issue is related to air temperature or not.

 

[87warrior]

The miss is related to cold temperatures...somehow.

This morning the temperature was a balmy 0 degrees. I drove a 1/2 hour at 70 mph without issue, stopped, ran an errand then got back on the highway. It started to miss fire 10 minutes into my drive with the cruise control set on 70. It continued to miss with cruise turned off. The miss was not continuous, but seemed to occur every 30-45 seconds. When exiting the highway the Cruiser did stall as I slowed for a roundabout. It just quietly shut off. It started back up and ran great at 30 mph through town. Still no CEL or funny reading with the Torque app.

 

[2001LC]

Bumer.

Then I say go back to post #4 and work through. Keep in mind cold brings out issues as it contracts and stiffens materials.

One other thought is at HWY speeds wind chill factor on undercarriage, lines, gas tank, etc would be bone chilling cold -50f or so. Fuel pump and lines could be affected.

Also the MAF has reads temp to send info to ECM, this may be issue. It's temp would be very low 0f at 70MPH, and you had recently cleaned. Hope you only used a MAF cleaner and did not touch wires or porbs.

Hope this is not a sign of Throttle body issues, which is know issue of 98-99.

 

[87warrior]

@2001LC - In post #4 you make reference to a VAN pump. I am not familiar with this term. Nonetheless, I need to replace vacuum lines as I believe they are original.

MAF was replaced with a new Toyota part last year. Torque app reads the incoming air temperature at 1-2 degrees above the ambient air temperature (consistently, even during a miss). MAF air volume also reads consistently.

I have had two APPS codes pop-up in the two years I've had this Cruiser, each time they self cleared. I only mention this because you hinted at the throttle body as a possible cause.

 

[2001LC]

Sometimes coils going bad will not set off a CEl, until they go dead. This is very common to your symptoms.

Sorry, VANE is the power steering pump. It has two vacuum lines on top coming off a control valve. I am always finding these lines bad. It's just two of many vacuum lines we need to check in our ageing fleet.

Power steering pump is on PS (RH) of engine front below air box.

I'm not saying vacuum leak is your issue. But basic need to be addressing first thing. Sometimes issues are a series of little things, that just do not setting off the CEL.

 

[87warrior]

Update: I have had no issue with the Cruiser the past few weeks. Air temperature has been been between 15° and 60°, until this last weekend.

Air temperature at 9° in the morning. Drove @ 55mph for 17minutes to the interstate. Once on the interstate cruise control was set at 75mph. Using the Torque App I kept an eye on the MAF. Generally it read about 425 CFM, gently fluctuating between 300 and 650 CFM depending on the road gradient. Incoming air temperature (measured with the same part as the MAF) read a solid 11°.

After 30 minutes on the interstate the Cruiser stumbled and it felt like another miss fire. MAF reading pegged to 1169 CFM. When the stumble quit the MAF returned to 425 CFM. I encountered another stumble an hour later and the MAF reading pegged to 1250 CFM, returning to normal once the stumble quit. The Incoming Air Temperature maintained it's reading through the stumble. Incidentally, I also viewed the Engine Load which was about 50% during normal interstate travel but would peg to 100% during the stumble.

MAF sensor was replaced just over a year ago with a new Toyota Part. I'll clean with the proper cleaner and check to make sure the plug is clean/tight. This may have been my last opportunity to test in the cold with spring rapidly approaching. The intermittency is making this a difficult diagnosis.

 

[Julian Stead]

Not a Land Cruiser but I have just had my knock sensor go bad on my corolla, it was causing a hesitation in cold weather conditions. It felt more fuel related but it eventually put the CEL on when it got really cold one morning, when the weather was warmer It didn’t play up. We have had a cold spell this week but after replacement I now have no hesitation at all. First Knock sensor I have ever changed due to a fault and I used to work on cars so I have fixed thousands of issues but this is a first.

 

[Greenehunter]

Hey guys any update on the issue??? I'm experiencing the same problem. Not sure what to do.

 

[KillerBox]

Hey guys any update on the issue??? I'm experiencing the same problem. Not sure what to do.

I am not sure about the original poster but, a new Toyota MAF sensor fixed most of my stalling problems.

I also replaced the fuel pump because it would like to stumble after coming off the interstate on a long road trip & transferring back to city street driving.

 

[2001LC]

Doing a few checks is starting point:
Look over engine; wires, hoses, battery clamps, leaks, etc.
Check for DTC in tech stream.
Check for misfires in tech stream under-load.

Note: In mud a you tube was posted recently. It shows we've an issue checking for misfires under-load. Has to do with a fault in tech stream. Guy shows how to dig deeper into tech stream and see if misfire is present.