2000 astro, rough idle, stumble from stop, hard warm start

[vivaleastro]

2000 astro with 376,000 on original engine . Hard warm start symptoms appeared first a couple of months ago. Van was due, so gave a complete 100,000 mile tune up (plugs, wires, cap, rotor, fuel, air, and oil filters, pcv). No improvement. Runs fine over 1000 rpm and gets great gas mileage. Initial codes for P0300 have now become mostly P0301. Have since swapped IAC valve, ignition coil, and distributor. Also swapped ICM, which made problem worse (and of course my local parts place will not take back ). Time to get smarter...scan tool shows misfire primarily on cylinder one, with lower counts on 2, 5, and 6, and none at all on 3 and 4. Flow chart in factory manual sends me to concentrate on compression or injector issues at that cylinder. Various injector cleaning products have not had any effect. What I can't figure out is why it would start fine cold (sitting >12 hours) with a clogged injector or compression problem. I did spray the throttle body (without removing it), with no improvement. Anything else I've read that would produce these symptoms (egr, pressure regulator, pump pressure) seems like it should cause a completely random misfire. So, anybody recognize these symptoms? At this mileage, I don't mind replacing parts, up to a point. Should I just go ahead and put new injectors in this thing? I do most of my own work, including all of the above, is injector replacement something I should be able to do with the factory manual at my side, or should I leave it to a pro? TIA

[MikeS144]

Have you checked your fuel pressure yet? This will tell you immediately if you have a leaking injector or regulator. I know on the vortec 4.3s with the "spider" you should see 60 psi at key on and it should hold pressure for several minutes. not sure which injection system your 2000 uses though....worth a look see. You can pick up a fuel pressure test kit from Harbor Freight for 20 bucks...

[vivaleastro]

Thanks for the reply, i've been meaning to update this post. Sent the truck to my pro and my problem did turn out to be a leaking fuel pressure regulator. Hopefully this helps someone in the future.

[Wmurky]

make certain your distributor vent holes are clean & clear, when they are blocked the cap and rotor can degrade very fast under damp weather conditions due to moisture build up inside the cap.