Idles very low after sitting for 1 week

[FiatRunner]

Hello all,

I went on vacation and left my car sitting for exactly one week. I come home, car starts right up fine, but idles super super low. Probably between 350 and 450 rpm. When the fan kicks in, it will stall. However, once you give it some gas, it runs beautifully, has plenty of power, and drives just fine.

I've never had this issue before, over the winter I'd start the car up every week but it would sit for 7 full days in between starts, and it would always idle very strong, between 900 and 1000 rpm once warmed up.

I did notice that it seemed to idle better when braking, as I did a few tests where I would put it in neutral at 45mph or so, and let off the gas. It would idle low but pick up in speed when braking hard. I have no idea why this is happening. The carb seems to be getting plenty of fuel, my filter is transparent and I can see that is isn't plugged and fuel is flowing just fine.

Edit: I also started to hear a sort of whistling noise, related to engine rpm. Got louder and higher pitched as rpm's increased but gets drowned out past 3000rpm. I was thinking vacuum leak, but wouldn't this make it idle higher?

Any ideas?

[FiatRunner]

I have an update.

Whistling noise is now a bit louder, still related to engine RPM only.

It isn't a vacuum leak, every hose and fitting and gasket has been checked. Is audible with the air filter on or off.

I was thinking it could be the alternator, as bad alternator bearings would cause a drag on the engine, but I don't know if it would cause enough of a drag to make it idle so low. Has anyone heard of an alternator going bad and making whistling noises?

[18Fiatsandcounting]

Has anyone heard of an alternator going bad and making whistling noises?

I haven't heard a whistling noise, but I have heard squealing or a light mechanical scraping sound. You could momentarily take off the alternator belt and see if the noise goes away. Don't run the engine for more than a few seconds like this as your water pump won't be working without the belt.

You could also remove the belt with the engine off, then spin the alternator pulley by hand. See if there is any noise, or if the pulley has any play in it.

As for the low idle, have you tried simply raising the idle speed to the nominal 850 rpm? Also, many Veglia tachs are quite inaccurate at low rpm, so it can't hurt to check with a good quality external tach.

-Bryan

[Nut124]

Did you say idle speed reacts to brake pedal?

If so, that would point to a vac leak in the brake booster.

Remove the vac hose from the booster and cap it off, see how it idles.

[FiatRunner]

Well, I’ve figured it out.

The alternator bearings are going bad, I took off the belt and it idles just fine, totally normal. When spinning the alternator by hand, you can hear that they’re going bad, and there is plenty of spinning resistance.

When you apply forward pressure to the alternator pulley while spinning, the amount of drag decreases significantly. I thought this was weird, but it would explain why there was less drag on the engine when braking hard.

I appreciate all the help! I’ll post an update when the new alternator arrives.

[18Fiatsandcounting]

Well, I’ve figured it out.

Excellent! The alternator pulley should spin freely by hand (when not charging the battery), so if you feel any resistance, the alternator bearings are bad. A alternator/starter shop should be able to fix that, or you can just buy a new or rebuilt alternator. The latter is likely cheaper.

-Bryan

[FiatRunner]

you can just buy a new or rebuilt alternator. The latter is likely cheaper.

So, I purchased a new alternator from AR. Turns out the old alternator was from some GM vehicle, and the yellow and grey wires were not connected to the alternator because they had nowhere to go.

I don’t know which wire goes where, and I don’t want to screw anything up by just guessing. Are you able to explain where or share a photo that would help determine where they connect?

[TX82FIAT]

AR at one point supplied a diagram of how to wire up the 95 amp alternator if that is what you purchased. I'm sure if you reach out to them they can tell you what wires go where.

[18Fiatsandcounting]

I did notice that it seemed to idle better when braking, as I did a few tests where I would put it in neutral at 45mph or so, and let off the gas. It would idle low but pick up in speed when braking hard. I have no idea why this is happening.

I missed this in your original post since I was focusing on the alternator. An idle speed that changes when braking can be a sign of the idle mixture screw being out of adjustment. A combination of extra air into the intake from the booster, and the fuel level shifting slightly in the float bowl, can cause a momentary stumble in the idle. Properly adjusting the mixture screw and the float level usually fixes that.

As for hooking up the new alternator, TX82FIAT's advice to call AutoRicambi is sound.

-Bryan

[FiatRunner]

An idle speed that changes when braking can be a sign of the idle mixture screw being out of adjustment. A combination of extra air into the intake from the booster, and the fuel level shifting slightly in the float bowl, can cause a momentary stumble in the idle.

As for hooking up the new alternator, TX82FIAT's advice to call AutoRicambi is sound.

I’ll make sure to call after work today, if there’s anyone that would know something that specific it would be them.

As for the idle, it would actually idle stronger and at higher RPM when braking hard, because there was a lot of forward-backward play in the alternator shaft and there was far less spinning resistance when it was pulled towards the front of the car.

I have no idea why, but at least now I’ve got the right alternator.