Need help with very fast idle shifted in park

[paximus]

Hey friends and fellow chevy truck lovers, I have a question I need some help with, I am new here so first of all let me say HELLO and thanks for having such a cool group. Here is my PROBLEM: I have a 78 chevy pickup and the last week when I put it in to park (its automatic transmission) the idle surges real high and super fast and it wont go down, does anyone know what may cause that and how I go about fixing it? I am handy and have tools etc, I have just never run in to this problem, it just started happening out of nowhere, the distributor cap looks ok, I havent checked the timing but the truck was tuned up and timing set about 7 months ago and its been running fine, it runs fine now but when I shift it in to park REAL HIGH FAST IDLE like someone is flooring the gas pedal. Please help with step by step instructions, this is one of my work/fleet trucks so we need it on the road and running to make money. THANKS FOR READING AND THANKS FOR ANY HELP YOU CAN OFFER!

[donut]

Fast idle cam on the choke? Can it be "kicked down"? Give the throttle a quick stab with your foot and it's supposed to drop back to a normal idle.

[paximus]

Originally Posted by donut

Fast idle cam on the choke? Can it be "kicked down"? Give the throttle a quick stab with your foot and it's supposed to drop back to a normal idle.

Right exactly, it usually kicks down when I tap the throttle but it is not now, I have checked all vacuum hoses and see nothing wrong. but when I close that metal plate inside the carb (dont know the name of it) it goes down to a real slow idle then I let go of that plate and the idle immediately starts going to fast again and just stays that way. Its probably something simple but I have no idea.

[paximus]

Can anyone help with some advice about this, I am outside working on it now but I dont even know where to begin, all I know is when shifted in to park the motor begins to surge and idle SUPER FAST and nothing seems to kick it down.

[Corts60]

On the passenger side of the carb is the fast idle cam.

Remove the air cleaner and look at the linkages on the passenger side of the carb. There should be a stepped cam lever on the end of the primary throttle shaft. These steps catch on a moveable linkage which is what is keeping your idle high. You may have to move back the the throttle to free up the cam and clear it.

If you take a a picture of that side of your carb for us, I can draw a circle around the part I am talking about.

[paximus]

Thanks so much for the help. I actually do see exactly what you are talking about and jiggling it around is getting a response, my neighbor stopped by, he works on his own cars and knows a thing or two and he said the choke is broken and showed me how and why he came to that conclusion, so I am going to go get a new choke I guess and take it from there. I think what you are suggesting is pretty much the same thing he did. THANK YOU I really appreciate the help.