I have a 1993 C1500 RWD truck with the 454 engine in it. I don't drive it much, it's a reliable work truck, but sits a lot of the time. It only has 130K miles on it. Not bad for a '93 eh? A few months ago it stalled when I was coming to a stop a few times. I had to push it out of the road one of the times and it took a bit to get it started again. I chalked it up to possibly being some "bad fuel" or moisture in the fuel lines. I drove it home after those few stalling fits without having it in overdrive and in lower gears in the back road to really get it hot. It started without issues many times when testing it after that. Then it sat for a few weeks. The next trip out I didn't have any issues at all, so I thought it was all resolved. Then the old guy sat for a few months. I just started it yesterday and it barely cranked over. Luckily the battery had barely enough juice to get it started. So I drove 10 or so miles away on an errand and it stalled on me when I came to a stop. The battery was weak so it didn't start and the battery died fully. After pushing it to the side of the road, I figured it might be the battery or the alternator.
So... Took the battery out and alternator out. The battery was dead, but took a charge and later tested good after the charge. The alternator also tested good, but the bearing was a bit gritty, so I decided to go ahead and replace the alternator and get a new serpentine belt. With the battery charged fully, new belt and new alternator the old guy fired right up without any issue and idled for 15 minutes for a good warm up. I figured I had resolved the problem and took off. 15 miles or so later it stalled while stopping, but fired right back up. Then did it again a little later. If I put it in neutral before coming to a stop and keeping the RPMs up, I don't have the stalling issue. Seems to be that it stalls when coming to a stop, in gear, when the engine is coming way down in RPMs. I put in new high test gas (3/4 of a tank, it was 1/4 full) and put in a fuel system cleaner.

So I'm at a loss at the moment as to what might be going on. It's weird that it's only when coming to a stop in gear that it will stall. Start it and let it sit in idle and it will run without issues. Drive it and while in gear come to a stop and that's when the stalling is occurring.

Thoughts? I'm pondering whether or not it might be low fuel pressure, so when the engine is coming down in RPMs after a bit of driving, it's not getting enough fuel and stalls out. But that's just a hunch.

Anyone else have a similar issue that I'm describing? If so, what was the culprit?

 

Probably time for a full tune up (plugs wires cap rotor all filters) if not done and it sits that much.
Also, our 93 5.7 Sub did this exact thing for about 6 months (and a daily driver) before totally dying - ICM in the distributor was the culprit

 

Inspect the IAC valve first - the issue you’re describing matches a faulty IAC perfectly.

Here’s a write up I did on the IAC some time ago -

https://chevroletforum.com/forum/198...urious-101819/

 

Definitely sounds like the IAC might be the culprit. Not too expensive or difficult to replace. I'll let you all know the outcome.

 

Whelp. The IAC wasn't it. The after start cold idle was better, but after it warmed up, while in idle, it shut down (no running around in gear, just sitting at idle). Starting back up and doing a few high idle revs, would shut down again. So it's not fixed with a new IAC.

What else should I look into? The tune up idea I'll probably pursue, just because I've never done one and I bought it in 2010 with 75k miles on it. It has 130k now. So worth doing.

 

Try checking for diagnostic codes, even if the SES/CEL isn’t on.

If no codes are stored, see what happens when you disconnect the MAP sensor and plug the port. A faulty MAP sensor could be causing the ECM to incorrectly adjust the idle speed/air-fuel mixture.

 

New MAP, so that's not the culprit.

Due for a "tune up" so will go ahead with cap, wires, plugs, etc. And will check for codes.

 

“New” does not mean “good” - that’s a lesson I’ve had to learn more than once.

 

Truth in that. I replaced the HPOP (high pressure oil pump) in my 6.0 diesel Ford Excursion to have it go out again in less than 15K miles later. Replacement parts don't always mean resolution. Since the tune up is really due (I believe the wires, plugs, cap, rotor, etc. are all original) doesn't hurt to be doing it. And although the truck isn't worth much on paper, it's definitely worth keeping around for the work the old guy does for us.
I'll keep y'all updated!