Yup, having some issues with the Bronco surging at idle and while driving. Pulled the carb apart today, reinstalled after I checked everything out. Still surging.

Anything I need to be looking at?

Hook up a vacuum gauge.

Take a look at your right foot. Where is it and what is it doing when you are surging?

Big vac leak.

How about ports out of the intake, like the one the brakes used to connect to (You have hydroboost now, don't you?).

I had Flintstone brakes before. So no vacuum port to plug.

Everything had been running fine since the swap over to 4 barrel, with the exception of an erratic idle. Well, that has apparently gotten much worse.

I've gone through the carb twice now with no luck in finding obvious leaks. The intake appears to have no issues.

I did order a part today and will see if that helps matters out Wednesday when it arrives. I'll keep you guys in suspense until the part arrives and I check for results. It's a funny story and I'm not proud of what I did. LOL

Have you done the old school check by spraying around the intake & carb area with starting fluid to see if the idle kicks up?

Negatron. But I will be doing that next. Hard enough to keep the damn thing running when the carb was on.

This sounds exactly like what was happening to mine a couple months ago. It turned out one of the vacuum port caps on the carb had cracked and actually fallen off. I couldn't see it because is was almost recessed back in under the carb.

But you've pulled your carb and it's working fine, so I'm out of ideas.

If it will help, you could come swap my Q-jet onto your engine and see if that helps. Wouldn't take more than 15 minutes to do a test. I'm actually riding the motorcycle most of the time, so you could even take it for a day.

Well, I've got my parts in and I'm about 75% done with putting everything back on and test firing. Work and a cranky baby have been getting in the way of turning wrenches. With luck I'll have it test fired tonight and report back.

I had a crack on my intake on an old F250 w/ 351W I had. I couldn't find it for months!!! I ended up taking the red dye & white powder spray (Dye penetrant )from my shop at work, spraying the intake letting it sit then spraying the white powder. You have to wipe the excess off REALLY good or it will leach, but if there's a hairline crack it will find it. My intake was an Edelbrock high rise intake manifold & I found the crack right at the threads on the front left headed down, was actually 3 different ones. We always called it crack finder, but any good welding store should have Dye penetrant test kits. There will be one can of red dye (Dye Penetrant) you let penetrate & one that dries to a matte white (Dye Penetrant Developer)that the dye in the crack leaches through. It might be worth a try! Some are more than others, but a basic kit should be somewhere between $20 - $40

So, I was pretty sure my vacuum leak was coming from around the intake/head surfaces. All troubleshooting of the carb and associated areas resulted in no fixes. Last night I pulled the intake and check out the gasket areas. Looked pretty likely that I did not have a good seal there. Dropped some new gaskets in and bolted everything back up. During the torque sequence I wound up snapping off the LAST BOLT I was torquing down. So, later today I get to repeat the same process all over except with a bolt extraction thrown in. Good times.

Went ahead and fired the truck up with the broken bolt in the manifold. After all, how much vacuum could be lost by one bolt, all the way in the back. Answer: 0.

Still have a surging idle with a bouncing vacuum gauge. And the only place I can spray starting fluid and get any increase in RPMs is near the air cleaner. So, I suppose the carb is the next thing to replace.

Anyone have a spare Edelbrock 1405 or 1406 on the shelf they want to lend me for a day?