Engine idle increases

[toml]

What would cause the engine idle to increase and stay at 1700 rpm after the car warms up? Everything was fine I set the idle at about 800 and all was well. As I drive and the engine warms the idle slowly increases. Any ideas? Thanks. Tom

[chrisfiat]

what year, what type fuel system, what mods have been done to the car, and if it's not a fiat, what kind of car are we talking about here

[toml]

Whoops, yes that would help. 1978 fiat spider. No modifications .

[131]

carbed or injected?

[TulsaSpider]

A 78 is carbed 1800. What happens if you pull up with your toe on the accelerator pedal? Will it go back down?

[manoa matt]

Either the choke is not set right, or you have a vacume leak that gets worse as the car heats up.

[So Cal Mark]

you might find the mechanical advance hanging up and staying advanced

[bobplyler]

I had the same problem, for about 15 years (I learned to live with it ). I rebuilt the carb, and replaced every spring in the carb. I made sure that the links were all moving freely. It finally went away when I replaced the carb.

[bradartigue]

78 would have a water-activated choke. The lever on that thing might be sticking or adjusted hamfistedly; easy enough to check: with the car dead cold and off set the choke by depressing the gas pedal completely. Then go look at the carb, the choke should be fully closed (flap over the carb barrel) and there is a lever part of the choke that holds the throttle slightly open. It should be pressing against the main barrel throttle lever. If you start the car and let it warm up fully then the choke plate should open fully and that lever should no longer touch the main throttle lever.

You also have a fast idle control capsule on a 78. Or at least I think the 78 had it. It is designed to hold the RPM at around 1600 while the transmission is in 3rd or 4th gear and the car is decelerating. If it is broken then the device may be activated all the time. To test, find the capsule on the firewall and disconnect the hose to the manifold. Block it off so the manifold draws no air. Start the car and warm up to see if this stopped the issue.

You may also have a poorly tuned carburetor, which runs OK when warming up to compensate for a bad/modified choke but then gets hot and just runs high. Tune the carb idle correctly - per FIAT's procedure in the shop manuals and reproduced in my manual (http://www.artigue.com/fiat) to see if the issue goes away.

[toml]

Thanks for all your help. I hope on Saturday i can sort this problem out.

[toml]

A 78 is carbed 1800. What happens if you pull up with your toe on the accelerator pedal? Will it go back down?

Yes, I tried that first and no difference.

[gchocevar]

I have the same problem with my 79 and a rebuilt ADFA with a 1800 manifold. I see that my choke fast idle lever is off the cam. When I kick the gas it drops down until I depress the gas again. I think its a kink in the linkage between the speed up control and the fast idle level.. My speed up control is blocked off. When I spray silicone on both linkages it works great until I start drivng again.

There is other good advice in this link that I have to try also. Silicon on the mechanical advance maybe? Hmmmm

Let us know if you find out anything.

[gchocevar]

I think I fixed my high idle. Even though the fast idle control was plugged (eliminated) it was still keeping the throttle linkage from closing until I kicked the accelerator a few times beween shifts and deceleartion.

I removed the forked lever off the front of the carburator that is attached to the fast idle control, retained by a small nut an circlip I replaced the lever with a similar ID and thickness washer, reinstalled the circlip and nut.

It now idles very smoothly at 850, and rpms drop as soon as I remove my foot off the accelerator.