1968 Bonneville Idle Stop Solenoid Function
 

Question...

'68 Bonneville, manual transmission, has idle stop solenoid on the quadrajet carburetor.
What controls the active, and inactive operations, has power to solenoid at all times...

Any ideas? Thanks, Jon

Anti-dieseling solenoid. Always powered whenever ignition is on.
Set idle with the screw on the energized solenoid.

I thought those were used to maintain idle when the A/C compressor kicked it.

Were they dual purpose on A/C cars ?

Did they come on any non-A/C manual trans models ? If so, what years & models ? :confused:

I'm not sure of that application in particular but those solenoids were used for anti run on or AC compressor compensation. The good news is regardless of the original intent you can use it to serve your need depending which power source you use to power the solenoid. In 69 they were used on the RAIV and the Sprint and in both cases they were for anti-dieseling-anti-run on.

that particular idle stop solenoid was used up through '72 model Pontiacs. High performance engine manual trans Qjet applications on '68-71 Pontiac V8's. Both T-400 & manual trans applications on '72 models. The small stamped steel bracket that bolted off the front quadrajet mtg bolt were either '68-70 or 71-72 style due to difference in design of the Qjet's airhorn.

At least on original '71 455HO T-40O equipped A-body's, the idle stop pigtail harness is tucked up & taped onto the body of the wiring harness/ no separate wiring harness for manual & auto cars.

Definately equiped on 1973 and 1974 SD455 for both manual and automatic applications. Ac or not.

Looking at the MPC and shop manual it looks like the application for those solenoids was a mix of idle stop and AC,

In 69 only the RAIV and sprints used an electric solenoid and it was for idle stop. Transmission played no role in application.

In 68 idle stop electric solenoids seem to have been used on all engines and transmissions across all models.

In 67 (and many earlier cars) an anti stall vacuum device was used on Many automatic cars to prevent stalling on sudden throttle let up. It temporarily raised the idle backstop position so the engine wouldn’t stall when you suddenly lifted your foot off the gas. 6cyl AC cars used the below device instead...

Also in 67 and earlier there was an electric speed up control (in effect a solenoid) used on 6 cal AC cars. The difference with this device is it was electric actuated but vacuum controlled. It raised the idle when the AC was on under low vacuum (high load) conditions . It was used on most 61-67 4 and 6 cal engines with AC..

For the 68 models curb idle is to be set with Air Conditioning OFF on automatic cars. No mention of manual shift cars.

Set idle with solenoid energized and de-energized (unplugged).

Yep, this ‘68 Bonneville is a manual trans non a/c car. Thank you all for the responses!

3 speed or 4 speed? Either way, it's a pretty unusual car - only around 200 Bonnevilles were built in 1968 with manual transmissions.

The same anti-dieseling is on my 72 Chevy Cheyenne pickup. I too was confused that it was always powered with ignition on. Reading the manual cleared that up. As mentioned, the idle is set by the plunger screw on the solenoid. The idle screw on the carb is set lower. Not sure how much lower. When engine shut off, the solenoid is de-energized immediately and the idle drops down because of the screw on the carb is set lower. This eliminates dieseling..

This is a 3 on the tree, pretty rare!