AZ455

Well I finally got a tach for the Olds, and was setting the slow idle today when I noticed something that doesn't seem right.

The service manual says to set the slow idle to 650 RPM in drive (solenoid energized) and 550 RPM in park (solenoid de-energized). Well, I set it to 650 RPM in drive by adjusting the solenoid screw, no problems. I then put it in park to adjust to 550 RPM with the carb idle screw and noticed the solenoid doesn't de-energize in park... Was my engine not hot enough or something? It had been running some time, but not driven. What de-energizes the solenoid?

Thanks.

MDchanic

Was your A/C on?

- Eric

AZ455

No, vent control in off position.

Rickman48

I thought the solenoid was for the A/C compressor causing a lower idle when on - and should be set with the switch in the on position!

boondocker

X2 ...according to my '71 manual.

AZ455

According to my manual for the 74 the solenoid energizes with the key in the ON position, which mine does (plunger out against throttle linkage). From how they describe it it only refers to it for setting the slow idle. It says set 550rpm idle solenoid de-energized in park, and 650rpm in drive - solenoid energized.

Mine never de-energizes, so if I set the idle to 650rpm with the solenoid plunger adjustment in drive, once I goto park I'm then idling at 800-900 rpm because the solenoid plunger is still pushing the throttle open some.

Unless it's really just an anti-dieseling solenoid and its supposed to stay energized the whole time until the engine is shut off? It's sort of vague in the manual.

Rickman48

Does anything change if in the A/C position, blower motor on?

AZ455

No, nothing different with A/C on or off, trans in or out of gear, or engine temp.

boondocker

Here's a explanation that might help...

http://www.corvetteactioncenter.com/...-solenoid.html

AZ455

Ah, so it is just to prevent dieseling. I suspected as much, but the name they give it misled me to think it'd change the idle as the car was running.

I ended up setting the idle to the 550 rpm in park they suggest, though in gear it drops down a bit more, but the engine seems to not mind the low idle speed... and it sure sound good that low...

Rickman48

And I don't think you have to worry too much about high idle with the choke on - in Arizona!
What's the coldest it gets there - like 40?

AZ455

Well, Arizona's a big state with very different elevations/climates throughout it..

In my part of the state, probably no colder than 15 degrees in an average winter. No hotter than the 90s in an average summer.

AZ455

So does anyone see any reasons that I shouldn't leave the in-drive idle at around 400rpm? That's with 550 in park.

Runs good, sounds good.

Rickman48

If it works, do it!

Junkman

The proper way to set this is to set the idle with the solenoid energized at the speed it calls for. Then disconnect the solenoid, and set the idle speed with the choke fully warmed and off at the 550. Once you have these two set, you can adjust the idle screws on the carburetor for the best idle, and then reset the other two. If the carburetor has idle screw caps, you can pry them off for a better mixture. Just don't tell the emission police that I suggested this. Then check everything one more time after you take the car for a drive around the block to settle out any "alignment" issues. If the air cleaner element is clogged, it is going to mess with your idle speed, so this is one more reason to replace a dirty air filter. If you experience "dieseling" when you shut the car off, then leave it in drive when you turn the key to the off position, and the "dieseling" problem is solved.