Repeated stalling

New member, 1st time posting. Hopefully I am not duplicating a previous thread, but I have not found one identical to my situation.
87 V20 suburban, TBI 350, TH400.

Went on a hunting trip last year, about 500 miles round trip. Did great getting there but on way back got stuck, replaced ignition control module in dist. and that fixed the problem (it was original and slightly rusted).

Got home, tried to fire it up a month or so later, wouldn't start. Fuel was dumping out of the injectors and out of the throttle bolt (that turns the blades, idk the part name), landing on the intake manifold. Replaced distributor, injectors, new gaskets for the TB, and ignition switch in the column. No more dumping fuel.

Here's the current problem. It will start up and idle nice for about 10 minutes or so then stall out. Every time. It will start right back up after that, then repeat the problem. It will not stall out if I unplug the tan/black wire in the driver engine bay area (vacuum advance I think?). However I don't want to run it around at base timing, I want it running right.

I have replaced: IAC, O2 sensor, MAP sensor, thermostat unit on front, ignition coil, all the vacuum lines I could see in the engine bay, PCV valve, fuel filter, I cleaned all grounds, checked fuel pressure it's at a steady 10 or 11 can't remember spec now but it was steady on the high end of spec pressure), and the previous owner had already deleted smog/EGR. I also checked TPS and oil pressure sending unit, those checked out. We also re-did intake manifold gaskets as there was a small leak in the back. Latest thing I've done is replace the TB, as there was a small leak in the side where the fuel was originally dripping out. I may have forgotten something but I think that's it.

In my mind it should have something to do with the vacuum advance system but I can't figure it out.
Vehicle is currently at shop for AC replacement and he is trying to diagnose it as well. Shop owner was a GM tech for 25 + years, he's seen a lot but is nearly at a loss.
Before someone says carb it, I likely will eventually, but would like to fix this first as it may still be a problem whether or not I stick a carb on it.
Any help greatly appreciated.
Edit - it was my mechanics idea to replace the TB because there was slop in the throttle (rod/bolt?) that controls the blades. He could manipulate a whistle sound by lightly moving it around, indicating a leak. Haven't heard back since.
Also have replaced spark plugs and wires.

T man said:

New member, 1st time posting. Hopefully I am not duplicating a previous thread, but I have not found one identical to my situation.
87 V20 suburban, TBI 350, TH400.

Went on a hunting trip last year, about 500 miles round trip. Did great getting there but on way back got stuck, replaced ignition control module in dist. and that fixed the problem (it was original and slightly rusted).

Got home, tried to fire it up a month or so later, wouldn't start. Fuel was dumping out of the injectors and out of the throttle bolt (that turns the blades, idk the part name), landing on the intake manifold. Replaced distributor, injectors, new gaskets for the TB, and ignition switch in the column. No more dumping fuel.

Here's the current problem. It will start up and idle nice for about 10 minutes or so then stall out. Every time. It will start right back up after that, then repeat the problem. It will not stall out if I unplug the tan/black wire in the driver engine bay area (vacuum advance I think?). However I don't want to run it around at base timing, I want it running right.

I have replaced: IAC, O2 sensor, MAP sensor, thermostat unit on front, ignition coil, all the vacuum lines I could see in the engine bay, PCV valve, fuel filter, I cleaned all grounds, checked fuel pressure it's at a steady 10 or 11 can't remember spec now but it was steady on the high end of spec pressure), and the previous owner had already deleted smog/EGR. I also checked TPS and oil pressure sending unit, those checked out. We also re-did intake manifold gaskets as there was a small leak in the back. Latest thing I've done is replace the TB, as there was a small leak in the side where the fuel was originally dripping out. I may have forgotten something but I think that's it.

In my mind it should have something to do with the vacuum advance system but I can't figure it out.
Vehicle is currently at shop for AC replacement and he is trying to diagnose it as well. Shop owner was a GM tech for 25 + years, he's seen a lot but is nearly at a loss.
Before someone says carb it, I likely will eventually, but would like to fix this first as it may still be a problem whether or not I stick a carb on it.
Any help greatly appreciated.

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We aren't going to say carb,that's going backwards. Let's see what your guy says I'm drawing a complete blank,with stalls,restarts immediately but never stalls in timing mode.

Ricko1966 said:

We aren't going to say carb,that's going backwards. Let's see what your guy says I'm drawing a complete blank,with stalls,restarts immediately but never stalls in timing mode.

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Here is a relevant question where I occasionally experience a similar but not always identical issue. When it stalls, can you immediately restart without turning the key back to the OFF position? In my case it will give no fuel or spark until the key is rolled back to fully OFF, then it will restart immediately. But if restart is attempted merely by rolling the key back forward to crank while the ignition is still on, I get no fuel or spark. I am curious to know if you experience the same effect. I have not yet attempted to run it in timing mode for an extended period since my stall outs happen very unpredictably, but if it starts happening more frequently that is a good test to do. I too am planning on going backwards to a carb if I can't find a resolution.

YakkoWarner said:

Here is a relevant question where I occasionally experience a similar but not always identical issue. When it stalls, can you immediately restart without turning the key back to the OFF position? In my case it will give no fuel or spark until the key is rolled back to fully OFF, then it will restart immediately. But if restart is attempted merely by rolling the key back forward to crank while the ignition is still on, I get no fuel or spark. I am curious to know if you experience the same effect. I have not yet attempted to run it in timing mode for an extended period since my stall outs happen very unpredictably, but if it starts happening more frequently that is a good test to do. I too am planning on going backwards to a carb if I can't find a resolution.

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Jump A abd B at ALDL next time,without cycling the key see if it will flash diagnose,not really looking for a diagnoses,seeing if the ECM is functioning when it dies.

Ricko1966 said:

Jump A abd B at ALDL next time,without cycling the key see if it will flash diagnose,not really looking for a diagnoses,seeing if the ECM is functioning when it dies.

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I will do that! I was not aware you could do that without turning off the key first. That may yield a previously hidden data point.

I will relay the message. I believe it would start up either way, but I know there were no lights coming on on the dash.

It starts up either way. No light on dash. I'm thinking it probably has to do with the open/closed loop system or perhaps air/fuel mixture?

Throttle blade shaft.

T man said:

It starts up either way. No light on dash. I'm thinking it probably has to do with the open/closed loop system or perhaps air/fuel mixture?

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The biggest difference between open and closed loop is feedback from the O2 sensor. You could unplug it and start and see if it stalls out. Unplugging it will likely make the SES light come on, but shouldn't prevent it from starting/running. But agree with above, that disconnecting the EST shouldn't change anything with respect to time of idle.

On a whim, you might try another ICM....perhaps it is the issue?

Does the SES light work? It should come on with key to ON and go out after you start it.

SquareRoot said:

Throttle blade shaft.

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We just sourced another TB because the first one was loose, you could manipulate different whistle tones or stop it by wiggling it. Waiting to hear the report from my mechanic if that solved it or not. Fingers crossed.

gmbellew said:

The biggest difference between open and closed loop is feedback from the O2 sensor. You could unplug it and start and see if it stalls out. Unplugging it will likely make the SES light come on, but shouldn't prevent it from starting/running. But agree with above, that disconnecting the EST shouldn't change anything with respect to time of idle.

On a whim, you might try another ICM....perhaps it is the issue?

Does the SES light work? It should come on with key to ON and go out after you start it.

Click to expand...

The SES light does work, and does turn off after starting.
ICM is new with the distributor but I know those are a bugger and it's worth having another one in the glove box. I may try another just to see.
I will give the O2 sensor idea a try.
Thank you for the input.

Update.
Got it back from the mechanic. He thought he fixed it with a new TB and IAC. On way home it stalled on me 5 times. Every stall was going into a deceleration. I ended up 2-pedaling most of the way home keeping it just above idle. Idles ok in gear (maybe low-ish to my ear?).
Tested it at home today and warmed up, it won't stall in P on N if I whack the throttle and release. Idle does go lower than normal for a half second then picks back up. It's only when it's in gear decelerating. Could it be the new but cheap distributor? Still an IAC issue? Or a vacuum leak somewhere? I don't think it would be a vacuum leak if it idles ok.
I would like to take it hunting this weekend so was wondering about disconnecting O2 just to stay in open loop but nervous that might cause other problems.