Rough idle-2007 4wd

I’ve got a 2007 with a 4.0, 4wd, Automatic. I’ve had what I assume is a vacuum leak for over a year now. But, I can’t find any bad hoses.
The problem- it only happens in winter. At first start up it idled a little rough. It would drive fine going down the road. But within the first few miles it would almost die when coming to a red light. I’d come to a stop and the engine would studder, almost die and then idle back up. It wouldn’t change when the engine got to operating temp. I’d have to drive it 10 miles or so before it would eventually idle normal. The next day it started all over.
Now, it will hardly idle when started in the morning. But it still eventually starts smoothing out miles down the road. The only CODES I have gotten were O2 sensors lean. I’ve used my scanner to monitor the parameters of the O2 sensors and everything is showing they are working properly. so what should I check next? I hoping someone has had a similar experience or can point me in the right direction. Thanks in advance.

 

Ive got a 1st Gen with the same problem. When coming to a stop and letting the truck idle, it sputters and revs low. This became a problem right after I removed the air intake from the air filter. I'm still yet to check for any vacuum leaks. maybe recheck the boot for cracks near the air filter? that's what everyone is telling me.

 

Sounds like a possible vacuum leak, while I haven't seen it on a Toyota yet on many other vehicles cold vacuum leaks are many times caused by aged intake gaskets. They leak when the engine is cold and when the engine warms up they expand enough to seal off again.
A smoke test would be the best way to find out if it's a vacuum leak and if there is one where it is.

 

Not sure if it's necessarily related but my truck idled low and sporadically, and it was fixed by a new PCV valve...

 

Take off the entire air box and clean it out.

Clean off the throttle body and plate.

You have xxxxxx miles of grime all in that airbox. All the emissions bullshit dumps oil/gas,etc and shit into the CLEAN side of the intake...

Might as well Change spark plugs while you're in there. And new air filter.

Then put a can of seafoam in your gas tank.

It just sounds like you need a tune up. Start there.

 

What’s a smoke test consist of? The truck has over 300k on it so there’s a good chance the intake gaskets are bad.

as far as a tune up the spark plugs are fairly new(15k miles) I haven’t cleaned out the intake so I’ll definitely try that, thank you.

as for the PCV, is there a way to test it?

 

Typically you block off the throttle body air intake and use a smoke machine to put smoke into a vacuum port and see if/where it comes out.

Not really, it's cheap and easy enough to just replace if it's suspect.

Cleaning the throttle body and unhooking the battery a few minutes to reset the idle would be a good first step and all it costs is a can of throttle body cleaner.

 

I agree with Dm, it sounds like intake gaskets that are flat and hard instead of thick and soft. The symptom happening more when cold is common in chevy/Ford V8s, I see worn intake gaskets quite frequently in those, especially at higher mileage.

If you don't have access to a smoke machine, and since they're at 300,000 miles old, I'd consider removing the intake manifold just for a look, and most likely replace them while in there

 

Like DM93 said, after you Clean the intake, unhook the battery. But to fully reset the computer, it takes 30 minutes, maybe more to have it disconnected.

Intake manifold gasket is probably $20 at any Auto store

At $300k I would consider checking the compression on all cylinders just for the hell of it.

 

Mine was running rough so I changed out all the ignition coils and spark plugs, fixed my rough running engine. All is good now

 

If it was the intake gaskets, wouldn’t it be worse when I punch the throttle than idle? Correct me if I’m wrong.

 

No, the air leak at idle is a larger portion of the overall intake air mass.

When the throttle is open more air is going through the MAF sensor than is leaking past it.

 

that makes since. Thank you, I’m gonna check that out!

 

At idle with the throttle closed, there is 18-21 inches of vacuum inside the intake. That will suck a lot of un-metered air into the engine. Un-metered meaning air that isn't being measured by the maf sensor. When that extra air gets to the exit side of the engine (the exhaust) the O2 sensors will see it and report a lean condition to the pcm. The pcm will respond by raising the fuel trims.

As soon as the throttle is opened, the vacuum inside the intake pretty much goes away, there isn't any suction to pull air in through the leak. There's much more air entering the engine (because you're on the gas and accelerating) but it's all going through the maf so the fuel mixture can start to correct again.

 

Thank you for breaking it down. This has been driving me nuts. I’ll update when I have it fixed.

 

I’ve got a 2006 with similar issues and codes. Had a couple misfires as well. So far we’ve put new manifold gaskets, replaced spark plugs, cleaned MAF sensor, and cleaned out the throttle body. Definitely running better but still getting the running lean codes. My mechanic suggesting it could be the fuel pump but doesn’t want to swap it cause it’s working fine. I’m guessing vacuum leak as well.