[Steve Sas]

How does exhaust leak cause a lean codes? Doesn't the gas leak out? Rather than fresh air getting in.

Does the rough idle happen all the time? best to do a log when this happens.

[studio54]

Originally Posted by Steve Sas

How does exhaust leak cause a lean codes? Doesn't the gas leak out? Rather than fresh air getting in.

Does the rough idle happen all the time? best to do a log when this happens.

A leak will allow fresh air to enter the exhaust between each power stroke during the cycle (pressure/vaccum cycles). If the leak is before O2 sensors it could create a lean reading.