Stumble after cold start

[Redsled]

I recently purchased a 93 Blazer with 350 TBI. All stock - no modifications. Overall, it starts(other than noted below) runs and drives great.

The only problem is on a cold start, it fires up fine, but then after a few/several seconds it will begin to stumble around and nearly stall. It will do this for about 30 seconds, then just snap out of it. I suspect because it goes into closed loop at that point? It only does this when cold. You can smell gas pretty strong when its doing this so something is making it run pig rich when its having its hiccup. Warm starts are zero issues. You can stop/start it 100x with zero problems unless its a true cold start.

Here is what I have done thus far. I also have a 91 k1500 with the 350 that runs with zero issues. So I have swapped the following parts over (one at a time) and started it up cold. So far, zero changes. Problem is still there after each “swap”.
MAP
IAC
TPS
TEMP sensor

I also pulled the solenoid under neath the distributor and checked it. It looks new so I didn’t replace it. I did clean it up and put new diaeletric grease underneath where it contacts the distributor.

Not sure where to go next?

 

[movietvet]

Temp sender for gauge or temp sensor for computer?

 

[Redsled]

Temp sender for gauge or temp sensor for computer?

Computer. The one up top next to the thermostat.

 

[movietvet]

Codes?

 

[Redsled]

Codes?

Good question. Forgot to say that…SES light only comes on after driving for a little while after the engine is up to running temp. Its a 32 which is a EGR/MAP code.

I was thinking maybe the fuel pressure regulator? But if so, I cant figure out why it would only fail during a cold start? If it was bad I would expect it would have other running issues?

 

[movietvet]

Sounds like you need to inspect the egr and passage.

 

[Redsled]

Sounds like you need to inspect the egr and passage.

I was thinking about that since it threw that code.

That said….please correct me if I am wrong, but I was thinking the EGR does not come into play until after the engine is up to operating temp? That it basically stays closed when its cold? If that is right, then is it still possible the EGR could be the issue? If it was stuck open I suppose that could do it?….just odd it can “correct itself” after about 30 seconds. But I am definitely not the expert on these motors!

 

[movietvet]

EGR could be a problem but maybe not the problem or it corrects itself when heats up and has the problem when cold. IMO, it is something that needs to not be overlooked.

 

[Schurkey]

93 Blazer with 350 TBI. All stock - no modifications.

on a cold start, it fires up fine, but then after a few/several seconds it will begin to stumble around and nearly stall. It will do this for about 30 seconds, then just snap out of it.

Connect a scan tool, find out what the computer wants you to know.

You can smell gas pretty strong when its doing this so something is making it run pig rich

More likely misfire, and the catalyst is damaged.

I have swapped the following parts over (one at a time) and started it up cold. So far, zero changes. Problem is still there after each “swap”.
MAP
IAC
TPS
TEMP sensor

Stop swapping parts, start diagnosing. What is the fuel pressure? How old are the usual "tune-up" parts--cap, rotor, plug wires, spark plugs, PCV valve? Initial timing correct? Does the IAC actually work? EGR functioning properly? Does the electronic spark advance work?

You NEED that scan tool connected to verify every sensor and computer output.

I also pulled the solenoid under neath the distributor and checked it. It looks new so I didn’t replace it. I did clean it up and put new diaeletric grease underneath where it contacts the distributor.

I have NO idea what "solenoid" you're talking about, or why it would need dialectric grease "where it contacts the distributor".

Photo(s)? Nicely cropped, resized, and in-focus, please.

 

[Sabinoerc]

I recently purchased a 93 Blazer with 350 TBI. All stock - no modifications. Overall, it starts(other than noted below) runs and drives great.

The only problem is on a cold start, it fires up fine, but then after a few/several seconds it will begin to stumble around and nearly stall. It will do this for about 30 seconds, then just snap out of it. I suspect because it goes into closed loop at that point? It only does this when cold. You can smell gas pretty strong when its doing this so something is making it run pig rich when its having its hiccup. Warm starts are zero issues. You can stop/start it 100x with zero problems unless its a true cold start.

Here is what I have done thus far. I also have a 91 k1500 with the 350 that runs with zero issues. So I have swapped the following parts over (one at a time) and started it up cold. So far, zero changes. Problem is still there after each “swap”.
MAP
IAC
TPS
TEMP sensor

I also pulled the solenoid under neath the distributor and checked it. It looks new so I didn’t replace it. I did clean it up and put new diaeletric grease underneath where it contacts the distributor.

Not sure where to go next?

I have a 93, same engine since new.
Other than basics like no broken wires, vacuum lines, etc. the first things I’d check is fuel pressure, make sure all the grounds are good, and for any codes.

The PCM has no feedback on fuel pressure and assumes it’s good. Marginal fuel pressure can cause behavior like you describe. Bad grounds, especial the one on the CTS causes noise which causes problems in the PCM. Trying to find problems without the basics confirmed and without codes is hard on these engines.

if you wanted to confirm whether it’s running better when going into closed loop there are pins on the ALDL connector you can connector or ground to have the CEL light flash differently when it goes into closed loop. I forget what but you can google. That said, even with that known it doesn’t necessarily narrow the problem set.
good Luck!