Mine's an '86 L98 4+3. Winter starts are great. But now that the weather is stating to warm up in Chicago, when I come back out of the store and do a restart, it cranks for about 4-5 seconds until it catches. Here's what I've done so far:
1) TPS and minimum idle are on (according to the procedure).
2) timing is on.
3) fuel pressure after engine turns off stays up (no leaking injectors?)

Spark plugs could use a change.

Next may / may not be related, but I was wondering about the cold start valve. The shop manual says it's adjustable? 1 turn out from bottom. Has anyone ever messed with this and if so, for what reason? I can't pull off the plastic cover.

 

I've not tried to adjust it but you could pull the connector at the CS injector. Though it would be harder to cold start it would tell you if the timer was the cause of the warm start problem.

Before you do that however, when warm starting the engine depress the accelerator fully for a minute before cranking the engine. If this eases the problem have the injectors serviced.

 

I already tried that and there was no noticeable difference in any start attempts. Warm starts were still weird.

According to the shop manual it looks like the "adjustment cover" just pulls off the CS valve. But it won't come off with a 'medium' pull.

 

I'm not sure about the '86 but my '87 manual says that the CSV isn't even used when coolant temps are above 95 deg. F. If its a hard starting problem with a warm engine, it's not the CSV.

 

Sorry, though I've had the cold-start valve out several times, I've not tried to pull the cover so can't realy help there.

 

What War Machine says is correct, but it can be misleading. The cold start valve (CSV) is not "supposed" to be used when temps are above 95 deg.

The CSV is not controlled by the ECM but is controlled instead by a cold start switch. This switch is a bi-metal thermo switch which is located at the front of the engine below the throttle body. If the engine is already warm or the temps are above 95 degrees, then it should not activate the CSV at startup. However, if the switch is defective it could be activating the CSV when it isn't supposed to. The switch is not expensive and can be replaced with simple hand tools.

It is also possible that the CSV itself is leaking. It doesn't add that much fuel to begin with and any extra fuel due to leakage will be easily compensated for by the ECM once you reach closed loop. At startup though the system is in open loop and a leaking CSV can add enough extra fuel to make warm starting hard.

The CSV is different from the other 8 injectors and is no longer available new by order from GM or anyone else. If you have a CSV problem you need to order a rebuilt unit from Rich at Cruizin Performance or have him or someone rebuild your existing unit.

As already mentioned, it could also be due to leaking at any of the other 8 injectors. I'd start by disconnecting the CSV and see if that helps. If it does, the problem is in the CSV or the cold start switch. If it doesn't, the CSV or one (or more) of the injectors is leaking.

Been there, done that. Good luck.