90 K1500 timing issue

[rhinostacy]

I have a 90 chevy K1500 with a 5.7L engine. I will idle fine when put in base timing, which is set at zero. When not in base timing, it seems to go full advance as soon as the computer takes over timing. When I unplug a major sensor such as the CTS, it will idle with about 25 degrees of advance. With everything plugged up, the timing will get erratic and it dies.
I have replaced the ignition module, plugs, wires, cap, rotor, computer, MAP, ESC module, and knock sensor. I have tested the CTS and TPS and both seem to be working fine. Any help would be greatly appreciated.

[Schrade]

Welcome to the boards there!

Strange - you unplug the CTS, and it advances. Normally, a default reading, like [no] reading from CTS, would make the computer go to default timing, which ain't not nowhere 'nary near 25 degrees advance.

Any codes?

What voltages did you get for CTS and TPS at idle?

[2000CAYukon]

I have the same truck except it is a GMC and I bought it new back in the end of 89. Normally, the timing will be 20 degrees advanced at idle after setting the base at 0.

A while ago, I was fighting a rough idle and found that the vacuum hose to the MAP no longer was holding a vacuum which would signal the ECM to add fuel and timing.

The other issue I had was the PCV gromet was hard as a rock and not sealing very well. After replacing the vacuum hose to the MAP and the PCV gromet, my idle issues disappeared.

//2000CAYukon