I finished completely restoring the vacuum lines on my Catalina to the factory configuration yesterday. I started the cold engine last night to leave work, and that was probably the smoothest idle I've felt this engine run so far. Before leaving work, I feathered the gas pedal on the cold engine to raise the RPMs. My aim was see if the high idle when it's hot might partly be due to the throttle binding up. Judging by the sound of the engine, I was able to replicate the high idle it does when hot on the cold engine by pushing the pedal and letting go. It took quite a few few taps of the pedal to get it to drop off again so I could put it in gear without doing a slight neutral drop. Where would I check for binding and lack of oil if that is what caused it to get stuck on the higher speed?
When I got home, I put the car in park after driving for 25 minutes and that still let the engine race. I was not able to tap the pedal to fix the idle as I had previously been able to in the parking lot.
Check all parts of the linkage system starting at the pedal and working back to the carb. Does the carb have a vacuum pull off and have you checked its operation?
This is something that really needs to be determined by observing the fast idle linkage and seeing where it's hanging up. As @Doc points out, also check for any vacuum-operated gadgets that may be engaging the fast idle and failing to release it.
There is a vacuum pull-off on the choke. I hooked a good sized vacuum hose up to it and sucked on the tube. The arm retracts, and extends back, though it took about a minute to fully extend again. The arm doesn't seem to be attached to anything. I attached an image of it.
I also have some new video I just took. I got it to drop down to the low idle again when it was warmed up. It took 3 or 4 sharp floorings of the pedal to get it to idle down to the 1st video. I put it in gear after doing the clip, and there was no jumping when I put it in gear, and it didn't stall. I touched the gas to move forward a bit, put it back in park, and the RPMs went back up to the 2nd video. A couple more sharp pedal movements wouldn't kick it back down again.
Slow Idle
Faster Idle
I'd almost forgotten what a nightmare emission-controlled carbs were in the late 1970s through early 1990s. (None of my 1960s and early 1970s cars ever had any of that crap on them.) Realize that the goal of the designers was primarily emission control. Driveability was a distant second on the list, serviceability maybe third if it was considered at all.
It appears to me that the vacuum canister on the left of your photo is the choke pulloff. Its intent is to start pulling the choke open as soon as possible so the engine is not running rich and emitting excess hydrocarbons. It should be connected to the choke linkage and would pull the choke partly open as soon as the engine starts up.
The canister on the right appears to be controlling the fast idle. In addition to responding to the choke, it may well kick the idle speed up if the AC is on (or it "thinks" the AC is on). Is that two vacuum hoses attached to that gadget?
The choke housing has a threaded fitting that is not connected to anything. Usually that would be connected to a a heat tube unless it's an electric choke. (The heat tubes typically rot away on old cars.)
I think you said you've obtained a shop manual on CD for this car. It should have a detailed description of what these components do, how they're connected, and how to adjust them.
The left side is the choke pull-off. I tested it last night by pulling the vacuum hose off the carb and sucking on it. The little arm retracted as the vacuum increased.
The thing to the right only has one vacuum hose, the lower one is running to the EGR valve from a manifold barb. The hose coming into the camera was a longer line I used to test that thing's responsiveness to vacuum. It also retracts with vacuum, whatever it is.
I've wondered what that threaded fixture is for. I have no clue where that connects to, as it has been missing since I first opened the hood of the car. It is a regular choke, all that's in that housing is a coiled up ribbon of metal that presses against a lever type thing that's connected to the linkages behind the housing.
Is there a more formal name for the choke-pull off and the heat tube? I can do a word search within the shop manual to see if it has anything on them.
If it's not an electric choke then that threaded piece would be an attachment for the heat tube, and that's probably long gone. Without the heat tube the choke won't work properly. The easiest thing to do would probably be to get an electric choke conversion kit. They're not very expensive and would have a new thermostatic coil with an electrical attachment for a heating element. This would be connected to a source of +12V when the ignition is on. I installed one not long ago on my '71 Ambassador for exactly that reason, the heat tube for the choke had rusted out and the choke wasn't working properly. Another approach would be to install a manual choke kit (I did that on my '67 Rambler) but you probably wouldn't want to go quite that far.
I remember my 1981 Toyota carbureted 22R with CA emissions. It had more plumbing in it than my house. There had to be a few hundred feet of vacuum hoses, a dozen or so thermal vacuum switches and assorted levers and weird springs everywhere. When I removed everything and switched to a Weber carb, I had two large cardboard boxes full of vacuum hose spaghetti.
Other than aftermarket fuel injection ($$$$) that's the best long-term solution for areas where emissions are not checked, just rip all that crap out and install a non-emissions carb.
I checked something out today in the vacuum lines and found a well hidden leak. The EFE valve (Early Fuel Evaporation) seems to be almost completely broken from its mount. The thing is intended to route hot exhaust back into the carb to more quickly evaporate fuel from the bowl, reducing warmup time. I sprayed that area with carb cleaner the engine racing, the idle slowed down. I read a faulty valve like this can cause exhaust to continue to be funneled under the carburetor and eventually lead to fuel boiling. I can imagine that causing the engine to not want to slow down once it's hot. Fuel evaporation could be giving it way too much gas for idle. I capped the line and am going to see what the effect is. Lubricating the linkages made the pedal easier to move, but had no effect on the engine operation.
@Doc and @Chuck_Tobias I assume this hole is where the stovepipe for the choke was supposed to be? I'm gonna get a repair kit from O'Reilly and try to replace that this weekend. Does that part of the system use any kind of vacuum to operate (vacuum leak I missed?), or does the hot air go into the choke just by convection?
That looks like it. There shouldn't be any vacuum there, just heats by convection. You can easily check that by putting a finger over the hole when the engine is running.
Chuck has the answer, just hot air, like politicians.
When I left work a few minutes ago, I took advantage of the cold engine and stuck my finger over that hole to see if it's pulling or pushing air, and it's actually sucking quite a bit of air. I was able to practically kill the engine by drenching the hole in carb cleaner.
I haven't seen that on any of mine but those late '70s emission systems have all kinds of crazy engineering to meet tightening standards with a carb. The designer's goal is to open the choke as quickly as possible. So they may be looking to pull hot air in there rather than relying on convenction, but if that's the case I'd expect the stovepot and heat pipe to be airtight - there wouldn't be a deliberate vacuum leak sucking unfiltered and uncontrolled air into the intake and messing up the mixture. If that setup is not airtight I'd have to say there's something wrong there. The shop manual emissions system section may have some info on this.