83 FB, AC works but idle not bumping from 850.
 

Hi Folks,

Oh these hot days. Good new is that the AC works (converted to 134a and charged up months ago) but the idle compensation function just stopped working as of yesterday. It had been working fine before that. White plug is in on the rat's nest and everything looks physically ok to my (untrained) eye.

Had a guy do the engine/tranny mounts a couple days ago, gotta be a coincidence!

I have made no carb adjustments ever, and it is all bone stock, ~32K miles.

Any thoughts on what to look at first? Thanks so much!

Tom

There's one of those little vacuum solenoids that controls it. It's been a long time but I thought it had an orange clip on it. Check all the wires on the rats nest quickly then look in the FSM. It'll tell you for sure.

If the solenoid is getting power when the ac is on then check to see if it is allowing vacuum to reach the diaphragm on the throttle linkage , if it is the diaphragm may have a hole in it. A vacuum gauge / pump makes it easy to diagnose.

OK cool, I'll check the solenoid and vac bits. Thanks.

Hi Folks, reporting back, fixed, simple.

Solenoid, vac diaphragm + tubes OK, no leaks. Some plastic-safe lube on the AC vac diaphragm plunger freed it up, and the idle jumps ~100 rpm under load (just under 1k according to the dash gauge).

For the curious, there is a little screw on top of the vac actuator that is very tempting to just go ahead and adjust. Wait. First you should make sure that the diaphragm and all of the mechanical stuff moves smoothly. Then , if you need to, do go ahead adjust that screw. Tighter is less tug, looser is more tug. I played with it first, and it caused surging. So I put it back where it was and then did the aforementioned lubing and moving bound up mechanicals. After that, no need to adjust that screw.

BTW, AC solenoid is the white one, far right.

Thanks!

Tom

https://cimg9.ibsrv.net/gimg/www.rx7...b339372e61.jpg

This is good info as I'm thinking about reinstalling AC in my car but with no rats nest and a modified
nikki. Knowing which vac solenoid I need and what drives it give me some clues.

I'm having the same problem on my SE. Not sure if the fix is the same with Fuel Injection.

Very informative post with a good detailed picture - welcome to the forum Toruki!

Thanks! I've been lurking here for years and find it really helpful.

Tom