What Can Throw A Lean Code?

[The John]

Driving around today I saw the check engine light come on and since I was close to the dealership that put in my new motor I swung by and had them scan it. It was giving a lean code, but with the motor running there in the bay, it wasn't showing a real time lean condition. We decided to clear the code and see if it comes back.

I know O2 sensors can cause it and we checked all the vacuum hoses and the intake is buttoned up pretty tight. Is there anything that could have caused it to go lean just for a moment to throw the code?

[DwayneJ]

An exhaust leak before the O2 can suck in fresh air with the vacuum behind the exhaust pulses, the O2s read that fresh air as a lean condition.

 

Not a diagnosis just another thing to look for.

[Jennabear]

Clean your MAF.

[The John]

Clean your MAF.

How? Spray contact cleaner in it?

Just asking because that's how I was told to clean the MAF on my '88 GTA and when I did it killed it. Just wondering if there was some other way.

[frupp]

I used MAF spray cleaner from the auto parts store. Worked great and the lean codes disappeared.

[Sierra54]

Almost positive this was the same code I had when the intake manifold gasket went bad.

[ChevyTech77]

Intake gaskets.