High idle on 1979 Spider

[RPihl79]

Hey folks, on my 79 spider I recently did a basic tune-up with new plugs, wires, distributor and filters. Since then, once the engine is warmed up it tends to idle high, say 1500-2000 rpm. I'm new to these engines and am looking for some guidance on the proper way to adjust that down, whether it's a timing issue or simply adjusting an idler screw, or something different all together. Thanks!

[aj81spider]

There's an idle adjust screw on your carburetor. There's an excellent booklet by Brad Artigue called "Fiat 124 Spider: Engine Maintenance and Modification" on the Fiat engine, including how to adjust your carburetor. It can be found on Mirafiori.com. It's worth downloading and following.

[RPihl79]

Awesome! I'll check that one out for sure.

[18Fiatsandcounting]

A high idle can also be caused by a leak in one of the hoses or devices connected to the intake manifold, so you might check to see that nothing got dislodged while you were changing plugs, wires, distributor, etc. Sometimes you can track down a leak by carefully listening for a sucking or whistling sound.

-Bryan

[RPihl79]

A high idle can also be caused by a leak in one of the hoses or devices connected to the intake manifold, so you might check to see that nothing got dislodged while you were changing plugs, wires, distributor, etc. Sometimes you can track down a leak by carefully listening for a sucking or whistling sound.

-Bryan

I'll check on that too. I know that there are a few lines that look on their last leg, so a leak is a real possibility.

[maxm50]

Spray carb cleaner on any suspected leaks. If there is a leak, the fumes will get sucked in and temporarily cause the idle to rise even higher. It’s a good way to pinpoint leaks. Some folks use propane also - I’ve never tried that personally.

[evrenosogullari]

The idle screw is a super easy thing to adjust with a wrench... also don't want it to be too low or car will die out when you are at a red light....

I was once broken down in the Holland tunnel because the car kept puttering out and turning up the idle a tiny bit got me on my way.

[SteinOnkel]

The absolute last thing to do for an issue like this to touch any adjustment screws!

Here's the diagnostic flow chart:

1) Compression test
2) Check valve timing
3) Check valve lash
4) Check ignition timing
5) Check vacuum leaks
6) Clean carburetor (or send it to me and I'll clean it for you)
7) If deemed necessary, replace broken o-rings and gaskets on carburetors
Now you may adjust it.

75% of all problems are cured with steps 1-5.

Stalling out at a red light is an indicator for other problems. These are silky smooth engines (if properly working); you can idle them at 400rpm if you want.

[SteinOnkel]

Spray carb cleaner on any suspected leaks. If there is a leak, the fumes will get sucked in and temporarily cause the idle to rise even higher. It’s a good way to pinpoint leaks. Some folks use propane also - I’ve never tried that personally.

Propane is better than carb cleaner, as the aersolized cleaner gets everywhere and will find its way into a healthy intake. Then your test has a false positive. Still, both methods are sketchy and not very good indicators.

The best way to check for vacuum leaks is to connect a smoke machine to the manifold and cover the throat of the carb(s).