Rough idle and blackish smoke on cold start

Hello everyone. I have been experiencing rough idle and black smoke from my non flex fuel 5.7 for sometime now. I live in northeast Ohio so it’s very cold here right now. But even on a mild 50f day it will do the same. No lights on the dash just a quick start follows by a rough idle for about 10 to 20 seconds with a greyish/blackish smoke from the tailpipe. After that it’s as smooth as ever. I bought it new back in 2012 and it now has 165,000 miles. Any help would be greatly appreciated.

 

How about pouring some Seafoam gas cleaner into the tank? Have at least 16 gallons of gasoline in the tank, and pour in the Seafoam. It is worth a try.

 

You wouldn’t be the first, second, or fifth person to come on here saying it’s a non-flex fuel only to find out it is indeed a flex fuel. Best way to check is the engine code or look at the gas cap.

 

If it is not flex fuel, I would consider a bad iat sensor that is built into the map sensor. Connect a reaeder before starting and watch the intake air temperature at startup and through those 20 seconds. It should match ambient temperature. Cold start only. If it is low by a good bit, that is what is driving the excess fuel.

 

Leaky injectors is another possibility

 

Would secondary air injection come into play with the above problem ? OP stated this is only in the first 10 to 20 seconds of cranking up.

 

No. That only pumps air into exhaust. It doesn’t affect mixture. A failure can force limp mode but that is more than 20 seconds.

 

Update: I cleaned mass air flow sensor and the throttle body and the pcv valve. I found a thin coating of oil inside the intake manifold. Any thoughts?

 

The PCV will send fumes from the crank case into the intake. Sometimes that adds some residue of oil, so much in some vehicles a catch can is needed to keep excess oil out of the intake.

 

My finger after swiping it inside the intake manifold

 

Time for a bath

 

Sorry I’m a noob. Would that include spraying carb cleaner into the manifold. Would that be a bad idea? Would I have to take the top off? No clue here. Is this indicative of bad valse stem seals? We got a high of 39f yesterday. Started the truck before doing the cleanings today and it started perfectly.

 

I would clean that throttle body. Don’t spray cleaner directly into it, spray onto a rag and use it to clean. I take would need to be removed for a thorough cleaning

 

Yes I did that already along with the mass air flow sensor. Bought the sprays for both and gave it a nice cleaning. I didn’t spray anything into the manifold though

 

How old is the PCV valve, and has it been changed? I change mine out very 50k miles on rides that use them.

 

It’s original. Was pretty gunked up. I shook it and it rattled (which I read was a good thing). Cleaned it with the same cleaner can I used on the mass air flow sensor. Going to get a new one asap.

 

You can take the pcv valve and shake it, if you hear a ball rattle it’s still good, if you don’t hear anything then it’s clogged and needs to be replaced, it’s only about $15

also you can take a rag and spray brake cleaner on it and wipe out the manifold, just don’t spray cleaner into it cause you don’t want it to leak down into the cylinders

 

Ok thanks Joseph. You answered a lot of questions there. Is this a sure sign of bad valve stem seals?

 

No - not a sure sign. How do the spark plug looks? Is the air intake system stock?

 

Stock air intake. Haven’t looked at the spark plugs yet. It’s 12f outside without the windchill. Waiting for some warmer weather. Like 30f lol

 

Is it burning any oil? Does the oil on the dipstick smell like gas? Do you have a way to monitor AFR?

Just running through what I’d be looking for.

 

I’ll check the dipstick when I get home today. I don’t have anyway of checking AFR.

 

Nope! Not a sign at all, the pcv is screwed into the valve cover so it’s bound to take some oil with it while pulling a vacuum; generally stuck ones will take way too much oil with them; but I’ve found the tundra one isn’t the best so I got a catch can that I just haven’t installed yet

also that throttle body is one of the worst ones I’ve seen, that should definitely help or solve your rough idle problem, as far as the running rich, has this just started with the weather?

 

Got it. Well started it today when I got home from work. Still having the rough idle and grey/black smoke for 20 to 30 seconds then it clears up and runs smooth. As mentioned before cleaned the mass air flow sensor and throttle body. Maybe now go through and change all spark plugs and coils? Does it matter what kind of coils. Rather not spend $400 just in coils

 

Also should I just take it to Toyota and have them look at it for $100?

 

Yes it matters what brand of coils. You’re better off leaving the factory ones with 200k miles than using Napa / Rock Auto specials.

 

How was the oil level? Did it smell like fuel? Have you verified the engine code under the hood?

 

No codes at all. Blizzard swept through and couldn’t see my hand in front of my face. Didn’t check the oil. High tailed it inside lol. What if it does smell like fuel? What would that be?