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'79 Eldorado Fast Idle Speed TOO FAST!


steve665

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I seem to recall a bad coolant temperature sensors on the Olds 350 would affect the idle speed. There should be a chart in the shop manual comparing resistance to ambient temperature.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I seem to recall a bad coolant temperature sensors on the Olds 350 would affect the idle speed. There should be a chart in the shop manual comparing resistance to ambient temperature.

When the engine warms up, the idle speed goes down like it should.

I'm just wondering if there is a way to adjust it so that it doesn't idle

so fast when the engine is cold. I gave away my shop manual with

a '79 deVille I sold three years ago.

I see there is a black, square Bosch device attached to the right side

of the throttle body that is set to the middle of a range fastened by

a set screw with a dab of blue paint intact. Would adjustmet of that

in one direction or the other change the fast idle speed?

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I seem to recall a bad coolant temperature sensors on the Olds 350 would affect the idle speed. There should be a chart in the shop manual comparing resistance to ambient temperature.

When the engine warms up, the idle speed goes down like it should.

I'm just wondering if there is a way to adjust it so that it doesn't idle

so fast when the engine is cold. I gave away my shop manual with

a '79 deVille I sold three years ago.

I see there is a black, square Bosch device attached to the right side

of the throttle body that is set to the middle of a range fastened by

a set screw with a dab of blue paint intact. Would adjustmet of that

in one direction or the other change the fast idle speed?

I wouldn't start messing with things without the shop manual - if your luck is like mine, you might buy yourself all kinds of additional trouble... :rolleyes:

I seem to recall that my carbed cars would idle what seemed too fast compared to today's fuel injected cars but that's the way they were. It could be the early EFI systems like what is on your Eldorado are the same way.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I wouldn't start messing with things without the shop manual - if your luck is like mine, you might buy yourself all kinds of additional trouble... :rolleyes:

I seem to recall that my carbed cars would idle what seemed too fast compared to today's fuel injected cars but that's the way they were. It could be the early EFI systems like what is on your Eldorado are the same way.

I gave away my shop manual so it pains me to buy another one for the $60 that they cost!

At some point, may have to. Meanwhile, I found this description of my 79 Eldorado's fast

idle valve on the internet:

"FAST IDLE VALVE

The EFI system fast idle valve, installed on the top of the throttle body, consists of a plastic body

that houses an electric heater, a spring and plunger, and a temperature sensitive unit.

The fast idle valve is connected electrically to the fuel pump circuit through the ECU. When the

engine is started cold, the open valve allows extra air to bypass the throttle valves.

The heater warms the thermal element which expands and forces the spring and plunger toward

the air orifice, restricting the flow of extra air and gradually reducing the engine speed to the normal

idle rpm. The fast idle valve has no effect after the thermal element reaches about 140°F. The

rate at which the valve closes is a function of time and temperature. The warmer the air, the faster

the valve closes. At 68°F (20°C) the valve will close in about 90 seconds and at -20°F (-29°C) the

valve will require about 5 minutes to close."

To get this valve to close faster, I wonder if partially blocking the air flow to the valve would

be effective? What do you think?

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You might also be able to play with the spring. Seems like weakening the spring might cause the fast idle to come off faster.

Thanks for the tip, Ed. I took the spring out. That disabled

the fast idle valve. The car has been sitting for six days and

it started and ran fine at normal idle speed (temperature here

is 70 degrees).

This is a fair weather car only, at this point in its life. Car shows,

cruises close to home, etc. If I need fast idle to keep it from

stalling I can fast idle it with the accelerator for a few seconds.

I hate the unnecessary fast idle that the earlier fuel injected cars

used to prevent any chance of cold stalling.

eld2.jpg

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