Hi, I have the typical 92' Olds 88 that is stuck in defrost mode. I know that there is a vacuum line in the engine compartment just left of the brake booster that is suspect. I fixed that leak but it didn't help any. Does anyone have any other ideas? I ordered a heat/ac control as the next measure of the goose chase but am open to suggestions.
The car has been acting weird anyways. I had an issue when I first got the car where it would stay stuck in park. I changed all the motor and trans mounts and that helped. Occasionaly, I have to rev the motor (which tells me it needs to build vacuum somewhere) in order to get it to shift out of park? Weird, right?
The check engine light comes on right around 45 but if I am cruising at 65 it goes away sometimes. The cruise control also acts weird on hills as it won't hold speed. (vacuum controlled as well)
I'm trying to figure this out but suspect it could even be a brake booster and with this car originally having life in Florida, I wonder if it is bad.
Well, if anyone feels like offering some advice, I could sure use it. I'm freezing from working on this out in the cold and my feet freeze from no heat in the car. Defrost only as that is the default mode...
Honestly, as you can tell, I've done my best to research before posting a new thread as to try and not miff anyone for being a newbie here....

you can plug off suspect components until your vac issues disappear golf tees work good. although the vents not working seems the likely suspect. i would take the vac connector off the back and put your finger on the source from the engine and see if you have a good vac and if you plug it the engine should smooth out. usually when a brake booster goes out you get vac going out when you press the brakes.

Defrost is the default mode when the HVAC control head fails. You may correct the problem with the new one you ordered.

Does your car idle rough? Are there any other signs you might have a vacuum leak? You can try spraying carb cleaner around your vacuum connections in the engine compartment. Any change in idle speed means you found a vacuum leak.

Have you checked the HVAC vacuum manifold that is located behind the glove box?

good idea with the golf tees! I'll try it tomorrow when I am free to work on the car again and let you know what I find.

and yes, the car does kind of idle a little rough but I thought it was just because of the miles being around 178K....It'* not surging or running really rough though. Could you tell me more about the vacuum manifold behind the glovebox? I have that area apart as I was checking the box diverter and it works witht he temp so I know that isn't the issue but there was a pink vacuum line that went up there abobe the computer. (It turned into a black one and I just assumed it is the one tha comes out the firewall to come back to the main tee fitting closer to the brake booster.
Do you think if I block off the fitting for the brake booster on the engine and notice a difference that this would identify the brake booster as the problem. i.e. cap off the port on the engine vacuum manifold that is on top of the motor.
Thanks guys! I really appreciate the advice and will try what you both have suggested and repost what I find...

one finally thing to note is that when I push the brake, it makes kind of "swooshing" sound at times? That'* what originally made me think the booster was bad and it is a main vacuum supply for everything, isn't it?

Read the following two threads:

https://www.gmforum.com/mechanical-134/climate-control-diagnostic-88-93-a-285427/

https://www.gmforum.com/mechanical-134/default-redirect-cooled-air-late-model-gm-cars-96-2000-a-279092/

I tried the new control/vacuum switch on the main heater control and that did not fix the issue which makes me believe that there is a vacuum leak under the hood.
Here'* a question I have: Do you think that the modulator on the front part of the transmission could be bad? Or is the cruise vacuum thingy ma bobber prone to failure as well, given the fact that it won't hold speed on a hill.
I guesss this is like peeing ion the wind with a vacuum issue. I don't see any really bad vacuum leaks, that is why I ask these questions....
Thanks in advance guys!
Randy

Go back to Justin'* post about blocking off vac hoses until you find the leak. If that doesn't work, get some carb cleaner and spray it around vac connections in the engine compartment. A change in idle speed means you found the leak. Pay particular attention around the EGR and the EGR tube.

You said the CEL is coming on. Get the car scanned for diagnostic trouble codes.

Where is the egr on the 92'? I didn't think this car had one?