Good day. I've learned way more about this truck in the past two days than I ever wanted to! Thanks to this forum for the information! I've read a lot, and I don't want to be that guy that just starts a new thread when something has already been addressed but when it comes to idle issues, each thread has a hundred different answers that seldom seem to work. The truck was bought new by my dad in 1987 and is a 86.5 with the Z24. It hasn't been running in a few years and my dad loves it (my mom hates it) so I thought I'd try to get it running again. Everything in the engine compartment seems to be original. There is no idle-up solenoid valve. It was never tapped into the TB from the factory so apparently it never had one. I got it started, but it wont stay running. Here's the skinny:

Difficult start. When it does start the initial idle sounds good then as it warms up (less than a minute) the idle drops rapidly and it dies. Hard to restart.
I can keep it running if I give it more acceleration but it will surge (buck, pulse) when I rev idle higher than about 2300 rpm.
-No leaking into the throttle body so ERG is probably good.
- Sprayed carb cleaner at all the vacuum lines and the under the ERG with motor running - no change in rpm.
-New NGK plugs (gappped to .032).
-Threw new wires, cap, and rotor at it with no change. Triple verified that the wires are correct on the cap and plugs.
-I can manually advance the throttle with the TPS. It runs longer at higher idle doing this, but eventually still dies.
-Voltage at the injectors, but oddly there seems to be 12volts at both wires on both injectors (I don't know if that's normal)
-Unsure of timing, but I would assume it's good, because it hasn't been altered and it used to run fine.
-When replacing plugs, both plugs for #3 and #4 showed rich (black and dry) while plugs for #1 and #2 showed a little lean.
-ECM is the old toggle style. I get code 23 and 24. 24 is expected as I have bypassed the clutch interlock awhile back.
-Fuel pressure is good with a steady 36 even when it's running rough.
-Fuel filter is new.
-All new vacuum lines but as you know, when working on the TB you have to disconnect some 1000 vacuum lines to get to it. I've tried it with the lines all vacuum lines connected and the air filter housing on - no difference
-Airflow sensor - vehicle it will die when I unplug it, so I assume it is working.
- I've checked all the fusible links and relays under the hood.
-I've removed, cleaned, and reconnected every body ground and motor ground I can find.
- I've unplugged, cleaned, and re-plugged the connectors for the exhaust temp sensor, coolant temp sensor, TPS, mass airflow, etc etc. both on the sensors themselves and on the harness. All seem solidly connected.
Sadly, it's hard to diagnose because it wont stay running long enough to test much more than what I've laid out here.

On a side note, if anyone knows of a source for the retainer plate for the speedo cable (at the trans) please let me know.

Thanks.

Are you sure you got all the vac lines on correctly? When I did the head gasket on my 86.5, I even marked the lines. Some of the labels came off so, of course, I connected them incorrectly. I recall having a similar issues once I restarted it. After a few swaps, I figured it out.

Thanks for the reply. All the vacuum lines are attached according to this schematic with the exception of my charcoal canister which requires three hoses intead of two. All vacuum lines have been replaced with new lines. One other thing I have noticed that seems a little off...This TB has no Idle-up sensor (that port is sealed from the factory) but it does have a FICD. Also, it has two injectors but the manual for the 1988 (mine is an 86.5 but I can't find a manual) says that the Z24 should have one injector. The wiring harness is 6 slots instead of 8. 4 wires to injectors and two to the FICD.

I'm working from an 1988 service manual that I downloaded from NICO. I think I really need a 86 midyear manual as I have found a few differences already. Timing in the 88 manual says 10 degrees, timing referenced on the truck says 5 degrees.

Found the issue(s). Intermittent ground to the crank angle sensor and vacuum leak between the throttle body and the intake at the gasket.