So I had this stalling issue a few years ago that just "fixed itself" Well the past few months it's been trying to stall when its in gear and when i put it in park RPMs shoot up to 2-3k.

Now, I decided to rebuild my holley 2bbl to try and find where the problem is. I rebuild it with a kit. Cleaned it in my ultrasonic cleaner, replaced float, choke pull off and choke thermostat and adjusted it as per the instructions. This fixed my problem with the high idle. The accelerator pump section was all gummed up and sticking. Runs so smooth now I can't believe it. But, I'm still having issues with it wanting to stall. In park it can idle all day long, When driving with foot on gas there is no problem, but when i'm at a red light and let off the brake the rpms randomly go from 750 down to 400 then back up or it will stall and die if i don't press the gas peddle. It doesn't do this all the time but enough that I have to "two foot it" so I can catch it in case it tries to die. Increasing idle rpm seems like a band aid, it stalls less but also idles too high. I dont drive with the AC because it causes even more stalling situations. No issues when accelerating, runs smooth.

I'm not sure where to go from here. The carb is rebuilt, I replaced all the vacuum lines because they were in bad shape. Vacuum port switches too cus they was only $5 on rockauto. Fuel pump, rotor, cap is only 3 years old, wires and plugs are new. Could this be pointing to a distributor problem? With the shape that my old choke pull-off was in I'm wondering about the diaphragm in the vacuum advance. I hate just throwing parts at it but on the plus side I know everything I replace is close to 4 decades old. Any ideas what to look at would be helpful.

1983 D150 318 2BBL Holley

 

A problem with older carburetors is sometimes the basic housing becomes porous over the decades. I'd had carburetors I just never could get right. See if you can find another carburetor and swap it on. I know at this age that may be difficult. My last carbureted truck I ended up swapping a 4 barrel intake on it. I then put an Edelbrock Performer carburetor on it. Go with a small one, 625 cfm or less. Larger ones don't do any good and may run the engine too rich.

 

I always like the spread-bore style of 4 barrel carbs. Small primary to promote velocity, and good fuel distribution, and large secondarys, for power when you needed it. And if you could keep your toenails out of the radiator, might even see better gas mileage.

 

I've thought about that but I already had the 2bbl setup so decided just to go with what I have. Last truck this era I saw at bone yard was picked clean in very short order. Might be a winter project if the carb is the problem still and I can find swap parts. I've read threads with similar issues pointing at leaks in the break booster or vacuum advance. Is there any way to test this? Far as I can tell the only things original vacuum related are the booster, distributor advance, egr valve and that charcoal canister thingy. I didn't replace the large vacuum lines but they looked fine. all the 1/4" and under lines are new as they were flimsy from age. Also put in new Tee's and checked the two check valves worked around the carb.

Edit: im not hearing any obvious noises for vacuum leaks.

 

Disconnect those vacuum lines, and plug them off. If the problem goes away, then you know where to start looking. If it doesn't.... need to keep digging. I have seen the holes the throttle shaft passes thru get wallered out, and you get a vacuum leak there.

Spraying around with carb cleaner, or brake cleaner, with the engine running, will also find vacuum leaks.

 

Well I think I'm in the right direction now. I don't see any changes when I spray the carb. Also plugged up the brake booster but that didn't help the idling problem. But, I noticed when I was spraying at the base of the distributor it backfired through the carburetor. There is another vacuum port switch back there too that I missed, so I don't know which is doing it but rpm's defiantly jump up when i spray in that area. This weekend I'll investigate when I have more time.

 

If it increases when you spray the base, you probably have a leak there. Did you reuse the base gasket/insulator? Either that is leaking or the throttle plate shaft may be worn out like Heyyou mentioned. There used to be a bushing kit available to fix that. Now, I don't know.

 

Thanks everyone. I got everything working fine now. I did have a small vacuum leak back there in the hose to my cruise control transducer but what was causing the issues was a rusted out failing distributor. I install a big cap HEI distributor and it runs like a champ again.