Recently my 96 Lumina (148,000) has begun hesitating when I've restarted it after sitting around for 30min-1 hour. If I restart just a few minutes after I turned off the engine or after a few hours, there is no problem. The car shakes quite a bit and comes close to stopping until I drive it for a few minutes. I've tried expensive fuel injector cleaner and premium gas as my first steps.

Previous maintenance: new spark plugs, tune-up done about 15K miles ago.

Heard all kinds of theories like the fuel pump, fuel injectors, cat. convertor, etc. I'm not a mechanic at all so I would like to narrow things done a bit if possible. I know enough to be dangerous, but don't want to get taken at a repair shop.

Ideas?

Welcome to AF.I'd check fuel pressure first, look inside the vacuum hose at the press regulator for raw fuel, scan it and look for pending or misfire codes, this is the basic initial diagnostics. A leaking injector can cause this but is more difficult to pinpoint. My 97 Lumina did this and I never really pinpointed the problem, never quit or got worse though.

Same scenario here. '96 Lumina, 3.1, 148K miles. (Is your's blue, too?)

I started getting protracted cranking after heat soak, but once it was running, it ran just fine. My initial suspects were just as maxwedge described, but there was no leakage at the FPR, the injectors and fuel rail held pressure just fine after shut down, and the ignition system was in good working order.

I finally decided to clean the IAC and throttle body. The IAC was dirty but not terrible, but the throttle plate and bore had quite a bit of varnish accumulation. After cleaning those, checking the PCV and CCV supply, if hasn't repeated the behavior. I know that when the coolant temperature sensor and intake air temperature sensors are reporting warm conditions on startup, the PCM will not step the IAC open as it does when the engine is cold. I suspect that the little bit of additional air provided by the TB once the bore was clean was enough to allow normal starts. if you don't find a fuel pressure problem, that might be something worth looking into.