I bought a 69 FB that had a 1977 Pontiac 350 installed. Stock down to the EGR valve (that has it vacuum source disconnected) Engine starts and idles fine, runs well. After running down the road a few miles, the engine will not return to idle and dies.

The ERG valve is disconnected from the external vacuum. Could it still be opening by manifold vacuum somehow or do they require an external vacuum to operate? I know these things can get crudded up, but with it disconnected I thought I was safe.

When the car starts cold, it idles fine. It has a hot air tube style choke which opens fully when warm. I can't figure out why it dies after stopping at a red light/stop sign. So weird. This is a 4-speed car. Changed the fuel filter, no vacuum leaks or fuel leaks on the Rochester Quadrajet. Running about 199F.

Any ideas to try? The weird thing is after it cools, it seems to run fine again until its driven far enough to warm it up. After it dies, I can restart it but have to apply considerable throttle to keep it running. Maybe the weights in the HEI are sticking?

No the EGR will not open without a vacuum signal.

My initial thoughts; vapor locking, idle mixture too lean, idle speed set too low, float level in the carburetor too low or the float has saturated and sunk.

Also, you can try this. When it stalls out, pull the air cleaner and manually hold the choke partially closed (about 3/4) and have someone try to start the engine.

It does sound like a fuel system issue.

Since it runs fine with the choke cold/closed, but won't idle after the choke is warm/open, I'd say something in the carb is the problem. May just need to screw in the throttle adjustment screw enuff to keep the engine running when warm.

Might also help to make minor adjustments to the idle air screws, to see if they make any change in idle speed.

Sometimes a Q-jet can get gunked up so that the idle circuit does not work properly. That would require a clean-out/rebuild.

I'd also check the initial timing, at idle. I use to run mine at aprox 12-13°.

"...Maybe the weights in the HEI are sticking?"

At idle, the weights should be pulled all the way in, by the springs.

A malfunctioning vacuum advance can cause idle problems. It should also have a constant, adequate vacuum supply.

Thank you for your reply. The thing that is weird is, when it cools off, like the next day, it cranks and runs great. You have to drive it enough to get it hot, and then it does it. So if the float were sinking, ect, it would likely keep running bad, not recover when restarted the next day. I don't have anything temp operated except the thermostat.

So if you shut it down for few minutes it will not run/idle well? It needs to go all the way "cold"?

Check your choke. Sounds like it's sticking shut. Put vac guage on it. Is it steady? What readings do you get cold (startup) and hot.

I'll check the timing and vacuum tonight. Drove the car to lunch, ran great, idled great. After it got to 200F, about 10 minutes, it started dying at red lights. I could restart the engine immediately and keep it running if I held the pedal down a little but. I stopped at a fast-food restaurant and the 10 minutes it took waiting, with the engine off, for food, it started up and idled fine again.

So, maybe the EGR valve only leaks when the engine is hot, and this causes a vacuum leak?

I might install a 1969 intake on it this weekend.

"...I might install a 1969 intake on it this weekend..."

A '69 intake will not work on '72-up heads, without mods.

The late heads have a blind hole, above the exhaust heat riser holes. The '71 & older intakes have a large rectangular exhaust crossover hole, on the passenger side, which will cause a leak.

There are fixes. The blind hole can be filled with furnace cement or equivalent. Some say you can cut a thin stainless plate, to cover & seal off the pass side holes. I've even read that some have used the Fel-Pro 1233 intake gaskets. I haven't used any of these methods. So, I can't say what will work best, or even that all 3 methods will work.

https://www.hotrod.com/articles/hppp-1301-pontiac-cylinder-head-modification/

https://www.summitracing.com/parts/fel-1233/applications/

OK, to help others, here is the problem I found causing this and the solution.

I removed the EGR valve and it was very sooty. The car would die after a warm-up at red lights even with the vacuum source to the EGR valve removed. I removed the EGR valve, tapped the openings in the cast iron intake and threaded in pipe plugs. No vacuum leak, no exhaust leak, no EGR valve. Appears as the car warmed up the EGR would leak more to the point the car would not idle.

The car continues to idle fine now and has more vacuum at idle than before. I did check vacuum, about 17 at idle. The timing was 8 degrees.