I am having a problem with my 1976 ‘02. Last week when I was driving, it suddenly would not idle although I could keep it running by holding the accelerator pedal down. I suspected a vacuum leak and replaced a very old brake booster hose with a new one. The check valve seems to stick a little but otherwise was functioning (preventing backflow). When I tried to start it, it would not idle at all but later maintained a higher idle (around 1500-2000) when I adjusted the idle screw on the carburetor (Weber 38). The in-dash vacuum gauge fluctuated slowly between 10 to 15 inches.
I worked on it some this weekend and here is what it is doing now. I can get it to start by holding the accelerator pedal way down but it won’t go above 1000 rpm, even with the pedal completely down, until it warms up some. Interestingly, the vacuum gauge shows it is drawing 0 inches. After it warms up a bit, it can be reved higher and vacuum gauge will read steady around 15 inches. When it is fully warm, I can get it to maintain an idle at 1500 rpm and the vacuum will hold steady at 18 inches and occasionally at 21 inches. Normally, it draws 20 inches at idle. I drove it down a residential street for about a mile and it seemed to have normal power when moving.
Any ideas what might be causing this?