So I assume we're talking about a vacuum issue. The thing that baffles me is, when I accelerate, isn't there *more* vacuum, and shouldn't that *close* the heater valve?

 

Less vacuum at any position other than "TB closed"....

 

Thanks Gretch.

 

Check your vacuum check valve (blue/black) mounted near the brake check valve. If the vacuum reservior doesn't hold vacuum, the heater valve will open up under open throttle conditions.

 

Will do Dave. I've been thinking vacuum issues anyway since she will stumble sometimes upon sudden WOT.

 

Heinrich
Second for the blue/black one way valve off the brake booster. Mine also failed and flowed both directions. The way I understand vacuum is that at full throttle the engine produces very little vacuum & produces max vacuum at no throttle while "engine braking". At idle my car typically pulls 14inches off the blue/black valve...which is more than enough to close the heater valve!

 

Brian ... sounds like an easy fix

 

Until you try to find a replacement for that "simple little vacuum valve". Not cheap or easy to find. If someone finds a good source for them, let me know!

 

I see these on the racks at local auto parts stores. Just a couple of bucks, although I haven't needed one.

Was going to say: check the check valve as well. OK, there I did it.

 

where abouts in the engine compartment are both the blue/black valve and break check valve located? anywhere near the master cylinder? I'm going to check mine.

 

Blue-black vacuum valve (p/n 843 820 675) I just replaced mine
before "Sharks in the Hood. $15 from 928 intern'l. Works great.

Check the 4-way connector, too (at the same location), $5
(p/n 117 078 00 45)

G'luck all.

 

My guess is that you have a vacuum leak under the dash. Check out http://members.rennlist.com/pirtle/svc_act.html