I recently purchased a chevy 2000 4x4 4dr 4.3 vortec.

The problem I am having is this, when cold the engine will stall, when the engine warms up it runs like a champ.

Here's what I have done so far:
radiator replace prior to purchase
Replaced fuel pump(AC DELCO) and spider(DELPHI)and yes fuel filter
Originally got a p0118 code, replaced temp sensor ac delco(coolant came out clean green) replaced lost coolant with water.

NOW:
fuel pressure is correct psi at pre start, idle and run.
Radiator coolant is green water mix with brown tint, radiator cap appear to have rust mud on it as well as over flow tank.
Oil appears ok(no milky or muddy indicating water) but to be certain I am changing oil tomorrow to make sure previous owner didn't use incorrect weight and replacing air filter(af replaced 4-5 months ago by me)

When it's started it runs a little rough, I notice the following, when it starts choking, the temperature gauge needle will bounce when the rpm bounces while stalling. Presently no codes.

I am plugged my drive right car chip in(moniters systems does not change anything) to see if i can find any thing I am missing.

After about 5-10 mins of stalling/hesitating it will run like a champ. If I let it idle for about 30 mins before driving it no problems at all. But this has dropped my mpg to 8mpg by doing this.

 

Looks like you have got a fleet out there to maintain, +5.
You seem to have hit some of the usual suspects.
Inspect cap, rotor, wires. Take out a couple of plugs and inspect.
Good clean of IAC, MAF, throttle body...........and so on.

 

Hey whats up you just explained almost exactly what is happening to my mother's Plymouth Breeze. I would test your head gasket have a compression test done on your cylinders. I haven't done this test yet on the Plymouth Breeze because of funds but it has the brown tinted coolant but nothing on the cap or no milkiness anywhere but the oil appears ok. It stalls when it's cold and takes longer to start and it goes away once the car is fully warm. Question do you have excessive smoke come out the muffler when cold starting your Blazer?

 

No it does not smoke.

Update, performed oil change with non syn and added slick 50 high mileage to it. Replaced the air filter(used fram until I can afford K&N) and plugged my drive right chip into it set to monitor air, fuel, o2 sensors. I am hoping this will show something.

 

Ok can you update us with what you find pls.

 

Came into this thread late, but just for FYI, I live in the NE and my Durango would do the same thing on cold days (even as warm as 30 degrees). It came down to the oil weight I was using. My guess was the oil was cold enough to make it too "thick" for the pickup or to get to the right places in the engine fast enough. Once I went back to the manufacturers recommended oil weights and stopped using any additives (like Slick 50) I never had the problem again. Granted, never had this problem with any of my Blazer's...but the symptoms are exactly the same as what I had with my Durango.

 

Green coolant, (ethylene glycol) is the wrong coolant. Needs to be Dexcool, (orange). When/if the 2 are mixed, you end up with brown mud in the cooling system, (might be why the radiator was replaced). The entire cooling system needs to be flushed, including the reservoir, heater core, block, hoses, radiator, and most likely replace the radiator cap as well, then fill with Dexcool and distilled water. This will not affect how it runs cold, but it will make your cooling system last longer

What is your fuel pressure? Key ON, engine OFF, and fuel pump running? Does pressure remain above 55psi for at least 10 minutes after the pump shuts off?

After the vehicle sets 8 to 10 hours, before you start it, check IAT and ECT readings on a scan tool. They should both be within 2 degrees of ambient temperature.

Might be a good idea to replace the distributor cap & rotor, (use AC Delco). Check the vents in the bottom of the distributor housing: if they are restricted, condensation can form on the underside of the cap when cold and cause what you're describing.

 

Update:

Replaced cap and rotor with ACDelco(with dielectric grease on all contacts).
Replaced plugs- ACDelco 41-993(with anti-seize lube) and Autolite pro Series Wires(with dielectric grease on all contacts).
Was not able to locate distributor vents, will try again when warmer and more light. Ran IAT and ECT tests via Car Chip Pro(I love this thing) see below.
Fuel pressure tested when it started this(tested correctly), will run again next weekend.

Found the following, #2 spark plug loose, all spark plugs incorrect gap(but ACDelco plugs mixed types[41-993 & 12607234]), after market cap(contact with rotor half the size of ACDelco) and rotor(corrosion on cap & arc marks on rotor) see below.

The vehicle did great, started in outside temp 26 degrees, did not sputter. But still going to find distributor vents, since its possible that cap was still warm and dry from changing cap.

Special Thanks to Captain!

Now onto flush and lots of other stuff.

 

Nice job! Sounds like you got it! Item #1 in the image below shows the vents. Some of the later distributors have slits instead of screens. GM TSB, (Technical Service Bulletin) instructs to remove the screens (if equipped) or clean the slits, (if equipped). Bottom line is, whatever it has, they need to be clear for adequate ventilation.