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77 Seville fast idle valve

Started by Kerry Lange, December 30, 2004, 03:39:41 PM

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Kerry Lange

Is there any way to disable or disconnect the fast idle valve on my 77 Seville 350? It is working as it should, according to the shop manual, but I find myself sitting for 5 to 7 minutes several times a day waiting for the idle to drop to a drivable speed. Even shutting off the vehicle for 30 minutes results in the fast idle returning. I understand the principles behind the operation, but would just like to either speed up the process or disable it all together. Ive already tried disconnecting the electrical connector, but this results in a permanent fast idle.

George Woodford clc21025

Why dont you replace the heater valve with another one? Check the yards in California, they sometimes have used heater valves for sale.  NOS are sometimes available here and there, but the part is GM/AC Delco discontinued; never was available on aftermarket.  My heater valve was performing like yours until I replaced it.  Idling at 2000 rpm for 15-20 minutes when you first start the car was too much fuel waste for me.

Kerry Lange

George, I dont think that my valve is defective, as I have a spare used one that does the same thing. My shop manual indicates that the fast idle will stay on for 90 seconds at 60 degrees F and 5 minutes at 20 below. Since my car has been recently brought into a winter climate, its the 5 minute waiting times that are now occuring several times per day. It doesnt sound like much, but time sure does drag when youre waiting for a cars idle speed to slow down to a drivable speed. Being an original California car, I dont know if the settings are different than a "normal" one. I doesnt have an air intake from the exhaust manifold like most cars do, so I supposed that the cold air from the air intake is having something to do with it also. I think the message above about putting shims in the idle speed valve is the way to go. I havent had the time to experiment yet.

Jim Smith

I purchased a nice low mileage 1979 Seville a few months ago and it has the fast idle problem also. It is a California car and has the same fast idle system as the 77s from what I can tell.  I am located in the central valley of Calif and have an acquaintance who was a mechanic working for a Cadillac dealership during those years.  He says that fast idle during warmup was a major customer complaint in those days. It seemed some had the problem and others didnt. He says make sure the valve assenbly is clean with no residue or varnish causing parts hangup. I bought a 79 Seville in 1979 with less than 10k miles on it, drove it over 140k miles and dont remember fast idle warmup ever being a problem. Doesnt make a lot of sense. Worked at GM Research Laboratories in Detroit in the 1950s and a lot of investigation was done trying to determine the wear rate of internal engine parts during a 20 minute warmup cycle. Tests indicated that more wear took place in those 20 minutes than during the next 8 hours of run time at normal operating temperature and loads. High rpm and high loading during warmup is not a good thing. Shimming the fast idle valve sounds like a wise approach. Sure will give it a try.  Jim Smith  

Kerry Lange

Rob, your post got me thinking over the past few days, and I came up with a slight variation on your theory. While placing shims in the top of the plunger would slow the idle down to a more driveable speed, it probably wouldnt change the time frame until it dropped to a slow idle. With driving conditions where I live consisting of driving on ice and snow a good portion of the year, I wanted the speed to drop pretty much as soon as I started the car. With that idea in mind, I removed the whole fast idle assembly from the throttle body, and installed only the seat and plunger. I then put a spare 1/4 inch drive socket in the top of the plunger and inserted a small wooden dowel into the hole in the socket. This dowel had been cut to take up any slack between the plunger and the heater control housing which was now back in place, minus the needle valve. Of course, the elecrical connector was left unplugged. This morning, I started the car in 30 below temperatures. The car started immediately and ran at a very slow idle. I was able to drive off immediately. As the car warmed up, the idle picked up only slightly. Ive kept the parts just in case I need to re install them in the summer, as the A/C may cause the idle speed to drop below an acceptable level. Thanks everyone for your opinions.
Kerry

George Woodford clc21025

I have heard of some owners using the 10 cent piece for those valves that dont fully close.

gordon24

how and where do you place shime show pic also.

spolij

Kerry Have you checked the choke? May be the fast idle cam is misadjusted.

Gene Beaird

Quote from: spolij on January 17, 2019, 11:54:38 PM
Kerry Have you checked the choke? May be the fast idle cam is misadjusted.

John, Roy is talking about a 77 Seville with EFI.  There is no fast idle cam.  It's all in the throttle body. 

@Roy, I know I've seen a description of of this job, but it's been years since.  If I remember, the fast idle valve has a cap that just rotates off and up, allowing you to insert a spacer right there.  Perhaps search for some postings by Bruce Roe, who's done extensive work on these 70's Cadillac EFI systems, maybe you'll hit on notes about how to do this mod, although I don't think Bruce really approves.   ;)
Gene Beaird,
1968 Calais
1979 Seville
Pearland, Texas
CLC Member No. 29873

spolij

Gene They really know how to screw up a good thing!