I did some major porting of my TPI base this winter, including 3" siamesing and gasket matching everything, including the heads. I had done the plenum and runners previous. I got the car running recently, and my scan tool indicates a lean condition at idle, with BLM steady at 137. I haven't driven the car yet. I am thinking that there is more, or better airflow into the motor, with all other things not changed. So more air would lean the mixture, yes? I can easily fix this condition with a new burn of the PROM.

Just wanted to see other folks' opinion.

 

Just porting the intake should not cause a lean condition. However a problem with the intake or TPI gaskets leaking will cause a lean condition. Did your idle jump after the work?

 

The idle was smooth and steady, after the usual warm-up period. I had bad gaskets BEFORE the porting work. The intake gasket was leaking antifreeze out of the motor, and into the motor as I found. Also I think oil was getting into cyl number 1&3. They were quite oily compared to the other cyl, as well as the injectors. The intake gaskets were in bad shape!!!

I had changed things in the PROM to match how the car was running before this work. Now everything is sealed up tight, and flowing differently, so it looks like I need to change things in the PROM to fix it.

 

If you've done a lot of port work, especially on a 350, I could see you leaning out a bit.