Hello new member I would like to say hello and help ? First I just picked up a 1990 formula 350 White from the original owner. She had it for 20 years never saw snow 52,000 miles very clean I have all paperwork. It was a dream find for me always wanted one. So my question is i have two problems the vacuum for the heater. That switch's the heat from floor two vent to dash is just hissing and wont switch it seems to be stuck.

The second problem is the car idles low around 550 rpm has a small shake seems low. Besides that the car moves its cold here in Chicago could the timing be off what should it be at and what is the right way to set it. I have read about a idle screw but the acronyms are killing me. I'm not sure how to set it any help would be great. Thanks heres some pics just got the car only pics i have sorry my buddy was in the car.

 

Welcome to the board. Awesome car too! The first thing I would do is take off your air cleaner and clean your throttle body really well using carb cleaner. Be sure to clean the back of the throttle blades too. While you're in there spray some carb cleaner down in that little hole on the bottom front part of the throttle body. That goes to your idle air control valve (iac). Also check the voltage on your throttle position sensor (tps). There is a tech article with instructions for this on this site.

You may want to take your iac out and clean it as well but if you do this you are going to have to reset the idle speed. Instructions for this are also in the tech articles. If I were you I would just clean the trhottle body really well and set your tps voltage. It is amazing what this will do for idle quality on a tpi motor. They are prone to carbon buildup in the throttle body due to the location of the egr valve. Doesn't sound like your idle speed is too far off. I believe 550-600 is about right for an automatic tpi. Cleaning will smooth your idle out for sure though.

As far as your HVAC controls go you probably just need to take remove the three screws holding the controls in and pull them out far enough to see the back. You might have to take your radio out too. Make sure none of the vac lines coming off the back of the controls have come off, broken, or kinked. Sounds like one came off based on the hissing sound. If that checks out you'll have to trace the vac lines. Good luck!

 

Forgot to mention, your idle speed is controlled by the ecm so don't mess with the adjustment screw on the throttle body unless you are prepared to reset the idle speed by grouning the computer.

 

Defrost is the default setting, so if that's the case you have a vac problem. If you can put your ear to the HAVC panel and hearing hissing, it's probably the switch.

JamesC

 

A bad idle and the door switching issue makes me first think of a vacuum leak. Our rubber vacuum hoses deteriorate over time due to exposure to heat and often leak. Sometimes they will even crumble when touched.

You can first check all the hoses for a leaking one, then attach a vacuum gauge to the idling engine and post the reading here. Replacing a leaking vacuum hose could cure both of your issues.

Jake

 

Thank you i will try and see if this works.

 

I was going to mess with that glad i didnt

 

I'm going to chase the leak down first maybe I will get lucky the car been good to me so far. Like the head lights didn't pop up fixed that for 65 cents took 5 hours. The alarm didn't work she gave me the paper work for it i called the company that installed the alarm. They were still there 20 years latter and they warranty it and gave me all new keys and new brain my cost 0 cents been getting lucky so far.

 

Yeah your vac lines are definately worth taking a look at given the age of the car. You should still clean your throttle body even if vac lines are your problem though. It's one of those little things that people overlook but it makes such a huge difference. Only takes a few minutes too. Let us know what you figure out.

 

So i found the leak Its on the switch looks like this peace can be snapped back on not sure. It shaped like a clip on the other side for what i can see cant get it to clip. inside If i hold it in place my vents flip and the hiss is gone. Heres some pics best my camera can do anyone know can this be fixed or get a new switch.

 

That's it you have it. Now you just have to figure where the clip that holds it in place is and put it back togeather. May have to get another piece from a junk yard.

 

I can't exactly tell from the pics but if you cant fix yours you can buy the whole assembly on ebay for less than $10 any day of the week. You can probably find one at a junk yard too but given that it is early Feb. and you live in Chicago, I'd check ebay.

 

Well napa had it for $36.00 GM discontinued it If any one can find it cheaper GM part #16032395