Engine Sounds Rough (Misfiring?) On Cold Start

2005 4Runner V6 4.0L — 220K+ miles

A code popped up for a 4th cylinder misfire approximately a year ago and I was advised to not worry about it (I'm fairly green when it comes to car maintenance, but learning quickly!). I'll never not seek a second opinion again. Anyways, I've noticed over the past month or so the engine is sounding/feeling pretty rough when I start it up in the morning or if it's been sitting for several hours, but then smooths out after about 20-30 seconds.

After watching a few videos, I suspect I might have coolant leaking into either the combustion chamber or exhaust manifold. I should not that the P0430 code has also popped up, but I've ruled out a bad catalytic convertor. The thing is, I haven't noticed a loss in coolant in the last month or so, but I was losing a good bit of coolant prior to that. I did put a different type of coolant (compatible) than what I was previously using. Not sure if that would make a key difference in the symptoms my car is having.

The car runs fine after it warms up, though. I'm not having any issues and sometimes I really push the engine (going 80+ mph up steep hills).

Can anyone point me in the right direction here? I'm thinking about doing a coolant compression test and going ahead and changing all of the spark plugs as well. I'd just like to the get this issue resolved before it turns into something worse.

Thanks,
thunderdustin

 

Hey Thunderdustin,

I wish I could help you, but I am having similar issues. I would never have thought of coolant leaking internally. I will have to check the coolant level. ? Did you have any overheating or temperature increase?

 

A compression test should help diagnose that issue. I assume you are low on coolant? Have you tested the coil on cyl 4? Sometimes when you have intermittent issues like that, a cracked spark plug can be the culprit.

 

My coolant was not that low...I added about 2 its and marked its level, I will keep an I on it, but not convinced its the head casket. I had checked all the vacuum hoses and removed the throttle body intake hose and air box to clean the throttle body.
the connection into the throttle body was cracked (dry rot). Ordered a new one and replaced it yesterday. Then I cleaned the MAF. and checked the all the wires (I live in the desert and desert rats have already chewed up my spark plug wires) and I noticed I had a loose ground cable going to the battery. The battery hold down bracket is constantly getting corroded. I think I will replace or repair the negative battery cable. After deleted all the codes (P0300, P0440,P0446) and driving for 30 miles, no codes have come back. Now I know the P0440 & P0446 will come back for the EVAP System. Time will tell on the P0300. Currently after these fixes she started up smooth and throttling at higher speeds was smooth (60-80).

If it were a cracked spark plug, I would think it would run rough all the time. I could be wrong.

Just curious, is the coil on the # 4 cyl a common issue. They were replaced 2 years ago. (Denso)

I will keep an eye on the coolant ( I replaced the radiator cap last year). If it starts to get low, it would be time for more serious action i.e. compression test, leak down test etc.

Appreciate your help, Static03

 

If you have a bad plug, but not completely trash, it would mostly be felt at idle. Might not even throw a code. Bad plugs tend to make coils go bad faster. Could always swap the coil and plug from 4 to another cyl, see if the issue/code moves with it.

 

I took your advise and swapped the #1 coil with the #3 coil.
Now it’s worse and throwing P0300, P0303, P0306. Hard to think it’s a plug

 

I’m having the same issues. Cold start rough idle. Codes p0304,p0306. I’ve swapped coils and it’s no better. Sometimes smell a little fuel. My coolant level is good, the level is the same as it always was. and not overheating. I’m in Arizona as well. I’ve inspected the wires and vacuum hoses. I don’t see anything loose or arching. Haven’t pulled the plugs yet. I just doubt it’s a plug because it clears up after a couple minutes. Just wondering what to do next! If I come across anything I’ll be sure to share. Thank you

 

Maybe you got oil leaking down into the spark plug? That will cause a misfire. Might need to replace the seals in the valve cover. Just throwing it out there.

 

That may be. I’m letting it cool down and going to pull the plugs on the misfiring cylinders and look for leaks.
Thanks
Jim

 

@james_b Miss is spark, fuel, compression or perhaps timing related. Get yourself a multimeter and check the resistance on all the coils and injectors - looking for outlier and comparing to spec. Do it when the engine is cold (and will miss) and hot (no miss). You say no better when you swapped the coils but did the miss follow the coil to the new cylinder? That's what you want to see. Pay attention to the condition of the connector, wiring and coil boots - look for tracking. Do the swapping one cylinder at a time and be methodical. If the miss does not follow, swap the plugs - again, one at a time and to different cylinders than you swapped the coils. If the miss does not move, put the plugs and coils back where they were, confirm miss has not moved and swap injectors.....again, one at a time.

 

Thank you for the info. The miss didn’t move after I switched coils. I still have an p0304 and p0306. Unfortunately it has to sit a while before it acts up again so the diagnosis is slow. But I will definitely try your method.
Thank you.

 

A misfire can also come from a bad fuel injector, I’ve replaced them for misfires on my Tacoma several times. Just my$.02.