Hi,
if anyone was unable to watch the little video of the misfire, please see the following link: My question is does it appears that the car is producing white smoke? Also does the misfire sound like knocking?

Thanks,
Orion

My car made the exact same sound once when I was being lazy and trying to clean the throttle body by
squirting carb cleaner in the intake boot instead of removing the throttle body.

Car almost stalled and then it knocked exactly like that just for a second as it ignited and blew it out.
This can be seen in your puff of black smoke when the knock is heard in the video IMHO.
Also, as mentioned above a head gasket, low compression, and anything else that hinders crankshaft
acceleration as measured by the ecm on the power stroke of that cylinder can be a misfire and this is
what makes these kinds of diagnostics so hard.
PS- Easy to spot a head gasket leak with boroscope your pistons will look shiny like they are steam cleaned. lol
That's all I got hopefully other members have ideas.

Thanks Margate. Yeah, I thought it sounds like knocking, and it does that almost every cold start. Just to be clear, it does look like smoking and for example, yours doesn't do this?
In regards to the throttle body, it has been removed, fully cleaned and installed with new gaskets, yet the issue remains.

I will pick up a borescope to get a better idea of the issue.

Thanks,
Orion

To be honest it looks like a head gasket leak after watching your video of white smoke & symptoms but then clears up when engine warms to operating temps so I'm suspicious.
Cylinder #5 misfire is on back bank and would be very expensive fix if it is the head gasket so trying to think of other things hoping you get lucky.

Can't help to notice that your misfire code Cylinder #5 is the port located closest to the Coolant Port on the Lower Intake Manifold Gasket but probably wishful thinking it can be your problem.



Hopefully others have ideas too.

Hi there. Any updates? My RX400h has similar sound/vibration in cold start-up for about 10 seconds. Car runs fine, otherwise. I’ve had this issue for over 5 years and didn’t think much of it. Just want to nip it on the bud now If possible.

I’m going to check the exhaust tomorrow morning but don’t think I’ve noticed anything strange.

only engine issue I have is rear valve cover gasket leak.

I did read on another site that a fellow 400h owner spent $2500 (in 2014 money) to fix the head gasket which fixed the issue.

In that case the engine was probably eating coolant running the engine for a bit burned off the coolant clearing any misfire. If you don't have coolant loss then that's not your issue.

I did read on another site that a fellow 400h owner spent $2500 (in 2014 money) to fix the head gasket which fixed the issue.

Head gasket is easy to diagnose:
Exhaust smells sweet and fog coming from exhaust
Coolant level going down
Look at the oil cap it will look foamy and/or white residue
Look at oil dpstick it will have coolant on it
Look in radiator it will have oil in it



If you don't have any of these symptoms your headgasket is fine. A badly leaking valve cover gasket could potentially leak oil into electrical connectors causing issues taht is still not too likely

I'm not buying the story that a head gasket was the cause of the other person's issues if it was better after a repair it was something else that was fixed

yea. no loss of coolant.. well, it did go down from high to low mark in 7+ years, which isn't alarming to me. I did top it off while doing front valve cover gasket/spark plug change. Need to do the back now.
Kinda odd noise and also vibrates/shakes the engine. There must've been someone who figured it out. I see lots of posts online with people have the same clatter noise in the mornings.

any codes? Could be lots of things:
Fouled plug
Bad or intermittent coil
Clogged fuel injector
Plug wire chewed by a critter
could even be deposits on a valve not allowing it to close properly

It is not a head gasket based upon what you've said (good thing as this is very time consuming and can be costly)

Start with the simple first - do a code read wtih TechStream or similar software to get deep into the computers post up what it says as a misfire should definitely cause a code

Not a bad idea to do teh below as routine maintenance it could also fix your problem but wait to see what the codes show
Next - add a pint of Seafoam gas treatment (Walmart) to your oil then run the car for maybe 50-100 miles get it up to temp this will really help get rid of a lot of probable sludge should be much cleaner when you remove your valve cover
I'd also suggest that since you're due to do the rear bank valve cover gaskets if you have not already done them i the last 50K miles or so replace the rear spark plugs (Amazon or RockAuto NOT eBay) with OEM or equivalvent
Replace the plastic connector pieces on the coils (Amazon or eBay)as they get very brittle - you remove the pins then put them into the new connector it only takes a small pick and a couple minutes to do
I cleaned my fuel injectors with a homemade tool - do a search to see the video I posted on this with Matt recently
I'd suggest replacing your fuel injector seals (super easy and costs under $20 think mine ran about $7 for all of them from eBay I believe?)
Replace PCV valve (RockAuto) - do not over-torque just snug it up. Look at the vent line make sure it is in good shape not cracked/old
Change engine oil and filter
Closely examine all your vent hoses, if any look older or cracked replace them they are cheap (mine at the air cleaner box were shot) (Autozone)
Last thing - clean throttle body make sure you have disconencted your battery cable now or while doing the above work that will reset the ECM adjusting for the newly cleaned throttle body
Clean everything up nicely remove all grease/oil so you have a clean slate

All that sounds like a lot of work it's probably 8 hours worth. It is not fun but isn't too bad you're engine will be in much better shape afterwards

If someone says it'll take 8 hours, it usually takes me about ~5 times longer because I'm slow and never have the perfect tool. haha.
I wish I'd get some DTC codes so at least I know what I'm up against. The car never threw a DTC. Car runs great after 10 seconds after a cold start. A warm-start = zero issue.
My game plan is to:
1. Run the BG EPR, MOA, 44k cleaner set. I figured this is as clean as my fuel system and engine will get using non-physical methods. [Ordered]
2. Change the rear valve cover gaskets along with new spark plugs and plug seals. [In garage] Front changed past weekend along with 3 new spark plugs.
3. Install 3 new rear ignition coils... Not sure about this.. it's going to be ~$200 for 3 Denso from RockAuto. I prefer to skip this. Or wonder if anyone used the cheaper brands with success.
4. Replace PCV valve. I think I replaced this like 8 years ago.
5. Fuel injectors? I think I'll look at tech stream to see if it's actually weak/blocked (by looking at fuel rate (?)). I know it's only $20 for the o-rings, but I want to leave it alone since it's pretty easy to get to, once really needed.

I did notice last week that the dealer broke all the ignition coil clips for the front 3 about 8 years ago. No cable ties to hold it either. The plug seems to be on tight though, i guess the airbox holds it down in a rx400h and doesn't let it move.
I'm wondering if there's something below the rear valve covers that could get covered with oil and cause this.
Any tips on trying to figure out which item on the data list could signal any issues? I'm really hoping to find an ignition coil plug not tight in the rear. Infact, i'm going to use a small video camera to see if it's unplugged later today.

Thanks again for coming to my TED talk.

I would not replace the coils unless given reason to and would never consider cheaper aftermarket ones If you gasket was leaking there's a chance it put enough oil in the spark plug tubes to cause an issue you'll find out soon enough when you pull the spark plug tubes off the plugs see if there is oil on the outside... also inspect the condition of the plugs. Any misfire should be captured by a proper higher level code reader. To replace the coil connectors is very cheap and very easy you'd be silly not to replace them all. If it were the coil(s) you'd definitely get faulty code readings but you should have codes anyway if misfiring. Almost everything mentioned above is either routine maintenance expected at higher mileage/later year cars OR should be on there as preventative maintenance so get it done regardless.

As for doing this job there are no special tools needed that I remember. I viewed a Youtube video on how to do the rear plugs it was very helpful however there was a lot of mention about how painful and impossible a rear cowl nut or bolt was to remove... I didn't find it challenging at all in fact I replaced it contrary to their recommendation. I don't have air tools nor a snazzy lift just a garage DIY'er so if this blond can do it so can you (I did use my Milwaukee electric socket wrench and their impact gun those are wonderful and really helpful!). PCV is under $10 at Amazon or RockAuto replace it while you're back there

Tip - when doing tougher, more complex work like this I love using egg cartons (see pic below) as a way of storing the nuts/bolts, each time I take off some nuts/bolts I put them into a slot then move to the next group... as I continue I have all the proper nuts/bolts/washers grouped together AND sequential order of removal/installation. I did this when totally disassembling my Honda Insight trasmission and did so doing tis job. Had I not done this trying to remember what goes where would be a nightmare! ummmmm be sure to take the eggs out first

okay. i used a small camera to see if the ignition coils were hooked up on the back plugs, they were.
I connected the tech stream before starting the car and looked at the data list. I forgot to press record. Anyhow i did see misfires in all cylinders (more in the 4,5,6) cylinders for the first 5 seconds of a cold start. I will try to re-record tomorrow.
After that, everything was smooooooth sailing as usual. It looks like I have the same problem as the OP.
If the ignition coils were bad, it should also misfire time to time while I'm driving right? which it doesn't.
My BG cleaning system is on its way, so I will do it within a week. Not expecting miracles.
I will be replacing rear plugs and valve cover gasket but need to decided whether to change the ignition coils too or not.
hmmmm... plot thickens...

Because the coil connectors are on doesn't mean they are properly secured adn conencted.... I would not worry about replacing coils unless the codes state they need it, the fact that they are working after a short time really doesn't poiunt towards that being the issue, there are a lot of other tings more likely causing this, do the easier, cheaper things that should be done anyway then proceed with a logical resolution process. What were the code(s)? You said it did show problems

Appreciate the help, all. I'm mudding up this thread, but i figure someone will read this at 2am in the year 2030 for their used RX400h purchased for $1,500.
I never had a DTC/MIL on this car except about 2 years(?) ago for the VSV tube. I still don't have any type of codes.
I'm uploading a cold start-up video from yesterday. You can hear it from engine start and end at around 12 second mark in the video.
The knock sounds like a Detroit diesel 18-wheeler start-up, but quieter. Ignore the sand-shaking sound. That's from the transmission(?) and pretty normal for hybrids. I've had it for 10+ years and doesn't bother me. I think ISC reset helps with it, which I haven't done since my battery disconnection past weekend.

Today, for the first time, I pressed the accelerator during start-up. Since this is a hybrid, I could step on it before the engine actually came on and "force" it on earlier.
No shaking with a little bit of gas. I'm talking maybe 20% foot pressure, no racing of the engine. In fact, I'm not sure if the RPM was any higher than a typical cold start (1500rpm?)
Does this mean there's maybe be an issue with the fuel system? Maybe the fuel injectors are dirty as you all suggested.
I know cars are drive-by-wire now, but I wonder if the accelerator pressing sent more fuel pressure which helped the sound. I guess Techstream can answer that.
Now is it the fuel injector, the fuel filter, etc...?

Thanks for the help. My PhD in YouTube-mechanics is not doing much.
Car is pretty much fine. Most people would not even notice there's an "issue." I'm thinking that if I do fix this issue, then the Elec->ICE switchovers will be a little smoother, also.

BG 3-stage liquid cleaning system gets here on Monday. Will try that first.
Then oil change, rear valve cover, rear plugs, and manual cleaning of the injectors...

Hmmm.. Perhaps the fuel system/injector suggestion from y'all was right?
I put a can of BG 44k fuel cleaner yesterday at the gas station and pumped almost a full tank of gas. It was very close to the F mark, I'm going to guess i had 15gallon out of 17.2gallon max. The can suggested 13 to 20 gallons. I wanted the mix to be on the strong side to really clean stuff out. I only drove normally for about 3 miles after, which included a mile on the freeway at 70mph. No racing.
Below is my misfiring at start-up (3-min time). It didn't sound as bad as my last start/video. Only one misfire here and there, when the engine first starts. Perhaps coincidence. Last graph is the RPM, if it's not zero then the engine is running on this hybrid. Didn't drive anywhere, just started the car in the garage. I will drive 6 miles tomorrow morning, so I will try to do a data pull again.
Previous start, last week, had about 50+ misfires at start-up in the high cylinder numbers (4,5,6). Not 100% on which exact one or two, didn't know I could record it. I just remember it being really high and the engine actually sounded like it always does.
[One-Month Update] I don't think the BG44k fixed it. At least I know my fuel system is cleaner though.

tech rx400h 2/03 - 1130am