2.5L ('98-'01) 99 4 Cyl. Code 0171 System too lean;

[Leigh]

UPDATE:
As stated, the truck would start, and run smoothly at idle, and I could rev it up, and it would run strong and smooth at higher RPM's, but when I let the pedal up to go back to idle it would abruptly quit running. As such there was no indication of a vacuum leak, ignition problem, or fuel pressure problem.

So, I cleaned the Mass Airflow Sensor, replaced both the EGR Valve, and the idle Air Control Valve, and now the engine will keep running both at idle, and "strong" and smooth at higher rpm's, but now when I let up on the pedal to go back to idle, it doesn't quit as did before replacing the EGR, & IAC Valves, but instead of running smooth at idle as it had before replacing them, it now, at idle, runs slightly rough, and periodically surges, and shakes. Back to square one, or is it two???

 

[pentode]

Sounds like progress to me, any new or changed codes?

 

[Leigh]

Haven't checked for codes yet. Unlike the V6, all these valves on the 2.5 are at the rear of the engine, whin two inches of the firewall, & surrounded by tubes, & wire bundle's---A real PIA--had me warn out!

II ran it after the valve replacements, and this time it shut down at idle, but the engine surged and shook, so, though the manual idle screw on the fuel control is not meant for idle adjustment, I nonetheless turned it in to get it running "somewhat" smooth enough to drive it.

It doesn't run as strong as prior to 'this" incident, and definitely lags on acceleration.

I've got a TPS sensor and a PVC valve still to put in.
If all that doesn't fix it, I'm thinking of either setting it on fire, or blowing it up for revenge!!!