Working on a 1992 inline 6.

We've replaced oxygen sensor, MAF sensor, Ambient air temp sensor in the manifold as well as the manifold gaskets.

172, EGO not switching; 412(cannot raise RPM) seems meaningless.

A later codes that occurred was 213, spout circuit open. It's been pulled and the circuit tested good.

Plugs are all fine.

Nothing changed from any of the above. Still runs pretty rough. Barely drivable.

 

FUEL FILTER?

 

Check fuel pressure and timing. That's all I can suggest other than pulling ECM and checking for leaking capacitors or burnt resistors on board.

 

How have you determined it's running lean.. . plugs are white?
What is fuel consumption like?
Does it idle smoothly?
A stuck open EGR valve will cause idle problems and make the engine run lean so that's something you should investigate.