Stumbling at 3200rpm with A/C on

[81 ZXT]

With the A/C off the car runs great. With it on it accelerates just fine til I get to 3200 rpm and then it stumbles terribly. If I get to around 3800 rpm and then turn on the A/C it stumbles just a little but barely noticable and will maintain pretty well at 3900 +. It started doing this last week. Ran OK with A/C on before. I could notice a difference in power with A/C on but it did not stumble. I changed the fuel filter (it was time anyway) and checked/re-gapped plugs. They looked fairly normal with maybe just a slightly lean condition. Some looked like they were burning/sparking on only one side of the plug. The way it acts to me is that is is electrical not fuel related. By that I mean when I am running at 3400 rpm and flip the A/C on, its like throwing a kill switch on and off. This is on a 1981 280ZX Turbo with A/T. Any suggestions will be appreciated.

[zKars]

I'm thinking you're getting a vacumm leak when the AC is on. This is the only system "shared" by the AC and the engine that would cause such a dramatic effect. As to where to look, well, everywhere vacuum lines are used by the HVAC system. Study the FSM for clues. Watch stumbling verses boost. If the issue goes away when on boost, and comes back when you're on vacumm, then that really points to a leak. Good luck, be methodical.

Jim

[81 ZXT]

Still having this problem. Looked on some other sites and 2 different guys said their AAC was bad. They said they replaced the AAC and that cured the stumbling problem. Looked thru the FSM and could not locate an AAC. Does anyone have any ideas?

[grantf]

Does you're car have the ac dash-pot thing that is actuated by vacuum? it should increase the throttle.

[sblake01]

Still having this problem. Looked on some other sites and 2 different guys said their AAC was bad. They said they replaced the AAC and that cured the stumbling problem. Looked thru the FSM and could not locate an AAC. Does anyone have any ideas?

The AAC vavle is located on the intake manifold and looks pretty much like an EGR valve. It's the furthest forward of the two. You have to look in the EF section of the 1981 turbo suppliment as it's not shown in the regular 1981 280ZX FSM. Edited August 9, 2011 by sblake01