So i've gotten my Blazer totally roadworthy, but I'm still dealing with the same stupid problem as I did the day I bought it. When you start it up, it'll run fine, then after a while it'll act like its about to die (idle goes way down), but then it immediately clears up. It does this all the time. New fuel pump, filter, spark plugs and wires, rotor, cap, IAT sensor, air filter and O2 sensors. Still same problem. Also, if i'm going down the road and need to pass someone, I usually have to floor it, and it takes about 3-4 seconds before the engine speeds up. Its quite annoying. I have no idea what to do at this point. (and just for those who might think so, I'm not throwing parts all on this one problem, the parts replaced are because of other problems) The only thing I can think of is maybe a clogged catalytic converter.

 

I don't have experience with a clogged catalytic converter but it sounds like a reasonable guess. The only other ideas are the air into the engine is not flowing well or the fuel pressure is dropping now and then.

Does it run fine no matter how you drive it for a specific period of time or does it only run fine if you do not gun it, irrespective of how long it has been running?

 

Take the cat off and shake it. If it rattles, I would look into replacing.

 

Do a check of all your main vacum lives, you may have one that is collapsing after it warms up.

 

I've considered maybe it being an issue with the IAC valve, because I just bought a '94 4 door (working a/c and heat!) ,with the same issue now after driving some time. Code on white one says IAC valve (code 35). But, since there is no emissions testing in NM, I'll just cut the cat off and put a pipe there to see if it helps. It runs the same at idle as it does at WOT. I'll also have to check the fuel pressure.
I also used the cigar smoke trick to check for vacuum leaks. Nothing seems out of the ordinary

 

I have a 2000 with only 6100 miles on rebuilt engine, .030 over bore, crank turned .010, heads totally redone, new billet distributor, 8mm wires, plugs, new cap, rotor, coil, ign module, oil lines, all new A/C components, etc. But I did not replace fuel injection components and had symptoms that have been posted on here before, such as : starts fine in morning but hard start after sits for a while, carbon out the tail pipe when warming up, strong gas smell," rough idle at stop lights", crappy gas mileage. So I bought a fuel pressure regulator from Ebay for 17.50 and free shipping, pulled upper intake plenum and this is what I did, found o ring gasket that goes around injector housing not fitting properly and was stretched out do to heat and age, throttle body gasket not installed properly so I put throttle body gasket in properly, didn't have to buy new plenum gasket it was new but could not find the injector housing ring sold separately so went to the section at O Reilly's auto where they sell blister packs of help parts and bought a coolant o ring repair kit for 6.99 which had the right diameter orange o ring in it and put it on the housing, completely cleaned the injectors, installed new fuel pressure regulator, new o rings on the the other plastic fittings on the plastic plenum, I had already done the throttle body mod so that didn't have to be done and put it back together and it runs like the brand new engine I built is suppose to, starts at the turn of the key every time no matter how long it sits and idles as smooth as grease on a pipe and cured the other symptoms as well, I could tell the fuel pressure reg was leaking because it had washed areas of the carbon away on the lower intake. I did this about 2 weeks ago and wish I would have done it a couple months ago but still learning this 4.3. Now that the weather is nicer here in Spokane, WA I will enjoy driving it a lot more. So you might try some of the things I did, my guess is the fuel regulator and maybe the injector housing o ring, it needs to be right so no air or vacuum leaks around it, Oh and I forgot also make sure o rings and washer are in right where fuel lines go into injector housing mine were not, black o ring then metal washer then yellow o ring last. maybe this will help.

 

And I forgot I had already replaced mt CAT conv when I first bought it, it was rattling so bad I was embarrassed to go through drive thru windows.

 

have you checked the ignition timing?

 

Didn't know if you were aware but timing is not adjustable manually, dist goes in and does not move after that you just tighten it down. It is done thru sensors and the computer.

 

Ahh - but the 93 as my 94 mounts a distributor ignition which requires a baseline timing...

... that being off, it may produce the symptoms 93BLZR has.