Hard Start and Stumble when starting

[1952Chevy]

99 K2500 Suburban Vortec 454

So recently replace the motor. Been running fine except for a misfire count of 2 at idle on the number 2 cylinder.

New parts on engine install.
- EGR Valve
- Distributor/cap/rotor
- Spark Plugs
- Plug Wires
- Every seal/gasket you can imagine
- Timing Chain/sprockets
- PCV Valve
- Oil Pressure Switch
- Head Gaskets
- Fuel Injectors
- Thermostat
- Radiator
- Oil Pump

I have a code for EGR not recirculating, and Bank 2 Sensor 1 02 sensor. The EGR I attribute to an exhaust leak(need to have a section of exhaust welded back in currently it's flex tube).

It's been running and starting fine, taking a little longer to start sometimes but nothing horrible. Well today it started I moved the truck, shut it off, and tried to start it again. It sputtered and shut off, then did not want to start. I had to give it some throttle to get it over the stumble on start-up. This has happened a few times since, but not every time.

What's everyone's best guess for the cause of the issue? My first thought is idle air control valve. Seeing as giving it throttle helps it. Doesn't seem like it would be a fuel pump issue, but that could also be on the list.

 

[Schurkey]

1. WHAT VEHICLE? WHAT ENGINE? WHAT COMPUTER?

2. What is the fuel pressure at prime? At crank? After the engine is running?

3. Was the camshaft "degreed" or just shoved in "dot-to-dot"? What is the cranking compression?

4. Connect a scan tool, verify all sensor inputs to computer, verify all computer outputs to injectors, EGR, IAC, spark advance, etc.

 

[1952Chevy]

1. WHAT VEHICLE? WHAT ENGINE? WHAT COMPUTER?

2. What is the fuel pressure at prime? At crank? After the engine is running?

3. Was the camshaft "degreed" or just shoved in "dot-to-dot"? What is the cranking compression?

4. Connect a scan tool, verify all sensor inputs to computer, verify all computer outputs to injectors, EGR, IAC, spark advance, etc.

Edited the post to include vehicle info.
99 k2500 Burb with Vortec 454
Haven't checked fuel pressure yet.
Camshaft didn't come out, and it was not degreed, but I made marks and it did not move, timing gears were dot-to-dot.

Havent done a compression test.

I have the torque pro app, I've checked the sensor it will allow me to and everything reads good. I get no readings for the injectors though, not sure if that's a PID issue or what's going on.

As stated I have the EGR and O2 codes that I know the cause. Figured the misfire count of 2 could be related to thise, and that only occurs at idle after its been idling for a while.

Spark advance varies but around 25 ish.

Once it's running it runs great. Just getting it started today was tough.

 

[Pinger]

Once it's running it runs great. Just getting it started today was tough.

I'm having a similar problem with my 350 Vortec and it seems to be worse in cold weather.
Like yours, mine needs a touch of throttle to fire-up and if I hold that throttle opening it will sit at around 1000 rpm but if I open the throttle further it is reluctant to rev any higher and my AFR gauge shows lean (though how trustworthy that is when the O2 sensors - despite being the heated ones - will still be stone cold). When/if it stalls, the process is repeated but at some point it clears (instantly) and is fine for the rest of the day.
Mine has had its butterfly stop screw messed with and I have the butterfly pretty much closed and if I do open it the starting is easier - but it seems to idle (when hot) higher than it should. Kinda points to the IAC valve but instantaneous loads (Hydraboost brakes, steering, gear engagement, etc) never catch it out).
Just occurred to me that my FPR might be sticking. Most of my running is on LPG(propane) so the FPR is sat in one place - fully closed probably without any fuel pressure behind it with the pump isolated (isolated to prevent the pump running all the time and the FPR being fully open for hours on end). I've had problems with it sticking in the past.
My pump is only a few years old and the wiring problem it did have is sorted now. I don't think the problem is there as when it it does come good, it runs perfectly well and never a problem when the engine is at temp (when it rarely needs more pedal to start).

 

[1952Chevy]

Started completely fine every time today. Idk what normal idle for the vortec 454 is, but I'm sitting at about 600 rpm.

Also yesterday was very humid and rainy, today was dry and windy.

 

[Pinger]

Think I've found the cause of mine being a pain on cold start.
It's a blow off valve and is located between the MAF sensor (and LPG mixer) and the throttle body.
An inlet backfire has bent it out of shape hence the gap at the top - and a sizeable vacuum leak.

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