Need help with very fast idle shifted in park - The 1947 - Present Chevrolet & GMC Truck Message Board Network

paximus · 11-09-2014, 07:04 AM

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 · 11-09-2014, 08:55 AM

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 · 11-09-2014, 09:42 AM

Quote:

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 · 11-09-2014, 12:49 PM

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** · 11-09-2014, 02:45 PM

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 · 11-09-2014, 03:14 PM

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.

11-09-2014, 07:04 AM	#1
paximus Registered User Join Date: Mar 2012 Location: tucson Posts: 39	Need help with very fast idle shifted in park 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!

11-09-2014, 08:55 AM	#2
donut Registered User Join Date: Aug 2009 Location: S.C. Posts: 1,593	Re: Need help with very fast idle shifted in park 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. __________________ '86 C-30 dually, 454/tbh400 '73 K-20 350/350/205 (sold ) I'm kinda like duct tape- no real purpose, but handy to have around.

11-09-2014, 12:49 PM	#4
paximus Registered User Join Date: Mar 2012 Location: tucson Posts: 39	Re: Need help with very fast idle shifted in park 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.

11-09-2014, 02:45 PM	#5
Corts60 Just here to tinker Join Date: Jun 2008 Location: Holland, MI Posts: 3,697	Re: Need help with very fast idle shifted in park 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. __________________ 78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/showthread.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 73 Chevy C20(Daily)http://67-72chevytrucks.com/vboard/s...d.php?t=852767 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(sold)

11-09-2014, 03:14 PM	#6
paximus Registered User Join Date: Mar 2012 Location: tucson Posts: 39	Re: Need help with very fast idle shifted in park 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.



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