2008 V8 mystery issue
 

Hey all

No idea how else to describe it but it sounds like my truck has the hiccups. Some background info first. Last Monday I changed the spark plugs on my 2008 toyota 4runner. However like the idiot I am I forgot to plug the MAF back in and started the truck up and it ran awful. I plugged it back in started it up but it was still running rough. I was getting the valve cover gasket changed later on in the week so I limped the truck to my local shop.

The truck was ready Friday and all seemed to be fine. I payed my bill and was on my way. However I went to merge onto the highway on Sunday and the truck wasn't reving correctly. Again the best I can describe it is as a hiccup as in the engine rpm would begin the climb, pause, then climb again. It only seems to be happening under hard acceleration or high revs.

What could this be? Something that I noticed was that after I got the truck back from the shop was that the coolant was low (the tank was almost empty) so I topped it off. I checked it again on Monday and the tank was almost empty again. So there could be a coolant leak somewhere? Only other thing that I can think which would indicate a coolant leak is that, I did a seafoam treatment and as I was letting the truck idle there was white smoke coming out from the right side of the engine bay. So maybe the head gasket is blown out on the right side? Only thing is that temps have been stable and the truck isn't over heating. I topped the tank off on Thursday and the level hasn't gone down. Maybe there's some excess fule in the engine? No codes, no knocking. I'll attach a video of whats happening. Best way I could get it to happen again was by putting the truck into neutral and giving it some gas. Other than this the truck runs perfectly fine.
Thanks for your time!

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UPDATE 06/27/21: Hello again. Trucks been back from the shop for about a couple of days and the hiccups are still there. As for the coolant leak the hose clamps for the upper radiator hose went bad so they replaced them. Leak solved!

They took it on a test drive but couldn't find any issues that would lead to the hiccups. The check engine light came on today so I took it to an autozone to see what the codes were. The codes were for the MAF, and that the engine was running too lean. Bought a new MAF sensor to get myself home and put it in. The Truck was almost stalling while I was stopped so I'd rather be safe than sorry.

Forgot to mention that the The shop that I originally took it to replaced the MAF, serviced the trottle body, and did an idle relearn. I started to notice the hiccup after that. Went out, bought a new MAF and dropped it in to see if that would fix it, which it didn't hence the post. So I'm replacing the MAF that I dropped originally to try to fix the issue in the first place. The fun never ends! Have an appointment with a dealership on Tuesday so fingers crossed they find something and fix it. Codes are P0174, P0171, C1201

UPDATE FOR THE UPDATE: Turns out the gas cap was just lose! Tightened it and the codes went away. Still had the hiccups though. Went ahead and checked everyrhinf that you guys reccomended and I couldn't find anything wrong. Gonna keep my appointment at the dealership just in case before I go on my 600 mile drive

There could be a few things here.

The coolant was low so you added more but there was an air pocket and when that went away it got low again.

I would disconnect the battery for a few minutes and let all the systems reset.

Smoke is like water, it finds the path of least resistance and openings. You would have to determine where exactly the smoke came out of, head gasket, valve cover gasket, Crack in the exhaust manifold etc....

Do a pressure test on the cooling system to make sure you don't have an internal coolant leak.

Thank you for the suggestions! I went ahead and unplugged the battery and let it sit for about 20 minutes. Plugged it bag in and let turned the key and it sounds like it's idling better but it did hiccup on first startup. Gave it some gas while it was parked and it was still hiccuping. Only thing is that there's what seems to be good amount of water coming out of the tailpipe. Not a good sign I'm guessing? Definitely doesn't smell like gasoline but doesn't have the consistency of coolant. Took a picture for reference. The trucks definitly never done anything like this before. I'll see if I can figure out how to do a compression test on the cooling system

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An exhaust will always have moisture in it until the exhaust gets hot enough to burn it off. The key is does it still have it after running awhile or pure white smoke out the tailpipe consistently. Go to a parts store, and rent a cooling pressure tester. Make sure it has the correct adapter for the toyota radiator. When you install it, pump up the pressure to about 15-16 psi and let it sit. If it holds pressure you're good to go. If it drops pressure at any point you have a leak. Then you will have to determine if it's internal or external.

Possible you got a faulty sparkplug, or a counterfeit sparkplug?

Check all your coil connectors, another member recently change his spark plugs and had a similar issue, he started switching some of the coils around to see if the "skip" would show up on another cylinder instead of the one he was having a misfire on and everything was fine, meaning he had a bad connection on at least one coil connector, most likely not plugged in completely since everything is fine after swapping some coils around.

Very curious how your coolant leak turns out, as I have a very similar issue. I just have been refilling the coolant occasionally enough and haven’t felt like paying the $$$ to be repaired. Every post on here about leaks seems to go back to the Water Pump/Thermostat housing (or specifically an o-ring), but thats not the solution for mine.

I have no idea about the engine “hiccup” unfortunately.

Ended up taking my rig back to the shop where it had work done to it. Turns out it's running lean without the check engine light on which would explain the "hiccups" and the backfiring that occasionally happens. They replaced the valve cover gaskets on both sides so maybe they forgot to plug something back in? maybe a hose or something, or even didn't tighten something down all the way. I checked coil connections myself and all are snug. As for the coolant leak, it seems to be coming from the upper radiator hose even though that was just replaced. I'll be hearing back from the shop later in the week and will update this post.

Could be a faulty/dirty MAF, maybe even blocked somehow. Did you touch the wires when it was out? Seems like its trying to breathe for air, but the MAF isn't allowing it to. Or its plugs/wires. I would check there.