Idle Stop Solenoid on Quadrajet

[Douglas L.]

When I purchased my 1972, manual, w/o air, I found that the incorrect Quadrajet was installed in the car. The carb installed was a 7042220 which is for a 454, automatic. The carb was equipped w/ a idle stop solenoid. I recently found the correct carb, a 7042203. The question is: Would a idle stop solenoid be correct for a 7042203 w/ no AC ? Thanks.

[Patrick H.]

Re: Idle Stop Solenoid on Quadrajet

Doug,

Yes.

See the link in my signature below for additional pictures.

Patrick

[David B.]

Re: Idle Stop Solenoid on Quadrajet

Patrick,

Do you know what was the purpose was of the solenoid on non-AC cars? I thought it was to maintain idle when the A/C load kicked in?

Thanks,
Dave B.

[Stuart F.]

Re: Idle Stop Solenoid on Quadrajet

The first real polution equipped cars were probably the 72's. They needed to have more throttle blade opening to maintain the desired idle speed. With this wider throttle opening, at shut down, it would have the propensity to "diesel" or run on. The solenoid was used to hold the idle (wider throttle blade opening), then withdraw at shut down to close down the throttle to prevent the dieseling.

Stu Fox

[Jack H.]

Re: Idle Stop Solenoid on Quadrajet

EXCELLENT explanation! However, there are other design aspects to the carb mounted solenoid than just that of thwarting the potential for 'dieseling' on engine shut down.

And, I would differ that '72 was the first year of serious air pollution control(s). The '71's cars which proceeded had the infamous, 1-year only, Combined Emissions Control system and also used a carb mounted solenoid to create two separate, electronically controlled, curb idle profiles in the pursuit of a cleaner exhaust profile.

But, the big picture is correct...the carb solenoid has NOTHING to do with RPM compensation for the extra load of the A/C compressor. The last year for that approach was '68-69.

[Patrick H.]

Re: Idle Stop Solenoid on Quadrajet

Patrick,

Do you know what was the purpose was of the solenoid on non-AC cars? I thought it was to maintain idle when the A/C load kicked in?

Thanks,
Dave B.

Nope, you're thinking of 71s. I've got one of those too.

There are long and thorough explanations of the 72 solenoid function in the Archives. The short story - in 72 the solenoid is used to set your idle. Do NOT use the screw on the side of the carb to set your idle. See Archives or your service manual for further info.

Patrick

[Stuart F.]

Re: Idle Stop Solenoid on Quadrajet

As I recall, the idle stop solenoid was used off and on at least through 83 on carb equipped passenger cars to boost the idle with the A/C on, specially on auto transmission cars. My 83 Camaro Z-28 HO had one, and that was with a five speed manual. As to it's application on Vettes, I'll leave that to the multi-year experts. My 63 L-76 don't got one.

Stu Fox

[David B.]

Re: Idle Stop Solenoid on Quadrajet

On my '69 BB with A/C, it seems to be for idle control, which caused my question. Based on what I read in the archives and the additional helpful info here, the function(s) seem to vary by year, and sometimes application. Thanks all for clearing it up.