EVAP canister and rough idle?

[chevrol8t]

I know this just may be a coincidence but I started getting a rough idle during cold starts which started smoothing out after my Tahoe warms up. Nothing major, no stalling or anything but every now and again my Tahoe will throw a lean code for both banks as well. This is a rebuilt engine with all new gaskets. All my vacuum lines look secure with no visible damage. MAF, TPS, IAC are all new and my air intake (Air Raid JR) is solid. A friend of mines asked if I checked my EVAP canister and after looking, sure enough one of the lines (out of the three it's the medium sized one) is broken and dangling like a loose tooth.

The canister is the original and a new one is on the way.

I know in the end I may have to take it to get it "smoked" for leaks but I was just curious could a broken line from by EVAP canister cause a vacuum leak. As weird as it sounds, as many vehicles I've owned I never had an EVAP issue and the last vacuum issue I had was due to a tiny vacuum line that controls my vent on my AWD Astro. So I'm new to this.

 

[SnowDrifter]

Brain dump of possible issues here:

It's possible, though an evap issue would generally show itself after the engine is warm. If you want to double check this, pop your engine cover off. There's a solenoid with a hard plastic line going to it on the top near your throttle body. Unplug the electrical connector, remove the hose, and start your engine. Place your finger over the top of the solenoid and see if you feel any suction. It's normally closed so there shouldn't be any thing.

Go around your intake and associated gaskets(don't forget things like injectors) with a can of starting fluid. You'll know you've found the leak because the engine will generally increase in RPM slightly in response.

It could also be the intake. It's not common, but still an issue where the aftermarket intake screws with the maf. It relies on a smooth, non-turbulent flow of air to operate. That's what that metal screen in there is for. Some filters provide choppy, turbulent air and throws it off. Easiest way to check is live data with a scan tool

How's your fuel pressure? Low fuel pressure can cause lean codes. Just chased that one down on my own vehicle.

Other possibilities are an exhaust leak. Exhaust isn't static pressure, it pulses. Those pulses and the resulting scavenging effect can suck in air, giving your oxygen sensors a false lean reading.

 

[chevrol8t]

Brain dump of possible issues here:

It's possible, though an evap issue would generally show itself after the engine is warm. If you want to double check this, pop your engine cover off. There's a solenoid with a hard plastic line going to it on the top near your throttle body. Unplug the electrical connector, remove the hose, and start your engine. Place your finger over the top of the solenoid and see if you feel any suction. It's normally closed so there shouldn't be any thing.

Go around your intake and associated gaskets(don't forget things like injectors) with a can of starting fluid. You'll know you've found the leak because the engine will generally increase in RPM slightly in response.

It could also be the intake. It's not common, but still an issue where the aftermarket intake screws with the maf. It relies on a smooth, non-turbulent flow of air to operate. That's what that metal screen in there is for. Some filters provide choppy, turbulent air and throws it off. Easiest way to check is live data with a scan tool

How's your fuel pressure? Low fuel pressure can cause lean codes. Just chased that one down on my own vehicle.

Other possibilities are an exhaust leak. Exhaust isn't static pressure, it pulses. Those pulses and the resulting scavenging effect can suck in air, giving your oxygen sensors a false lean reading.

Thanks I will try all suggestions!

 

[chevrol8t]

Just an update. First SnowDrifter thanks for the help. It was the intake gaskets. Finally got them replaced yesterday (Yeah I know it was a long time since this posting but work has been nonstop!). Old gaskets were hard as rocks providing no sealing. New gaskets solved problem!