OK, I got distracted with another project. Sorry for the interruption.

Now that I'm again investigating my FI problem, I have satisfied myself that the issue is not the MAP sensor. At the MAP sensor connector, the +5 volts and Ground are present, and when I apply vacuum to the sensor the center output contact swings from +4.6 volts to +0.7 volts. I also traced the continuity of the sensor's output conductor back to the ECU. It was good and didn't show any intermittent behavior.

Now, since the general opinion is leaning toward a vacuum leak, is there any benefit in measuring the manifold vacuum? If I had a vacuum gage, are there any meaningful readings I can take that might point me in the right direction? Where would I connect the gage? What values should I expect to see?

The PCV valve has been eliminated, so it is not the source of a leak.

 

I'm resurrecting this thread merely to bring it to a logical conclusion. For those of you who had the interest (or fortitude) to read through it, you'll be happy to know that the root cause of my idle problems was a tired fuel pump. For those of you who helped me figure that out, thank you very much.

Actually, I owe Ruffneck an apology of sorts because he suggested early on to check the fuel pressure, but I figured since the engine would start and run (though with difficulty) that it couldn't be the fuel pump. I could SEE that the engine was getting fuel. True it was getting fuel, but the pressure was too low. Well, I have now been educated thanks to you. Had I listened to you then, I could have saved myself much time and money.

In a nut shell then, if your truck begins to suddenly idle strange and it won't take throttle, be sure to verify that the fuel pressure is correct before you waste a lot of time and $$$ looking elsewhere.

Cheers