Hi all. Im new (first post here) and have just recently purchased my first Firebird. It needs some lovin, right now its in the process of getting a new windshield frame grafted on due to rust around the t-tops but there are other issues that need addressed before it rolls back out of the garage. Its a weird auto cruise issue at about 1800rpm when the car warms up to operating temps. You let off the gas pedal but it keeps right on going like you didnt. It wont let off until you hit the brakes and hold them for a few seconds and it lets go all at once, no slow release. Now, before you think its a sticky cable it gets weirder. When you are at idle and turn on the ac everything is fine until you take off and then try to stop. Sticky throttle that wont let go til you turn off the ac and its immediately released. I learned this the hard way on wet pavement trying to stop with the ac on defrost to clear the windshield... Any idea what could cause this? Im also having problems with the secondaries opening up when you really feed it the skinny. The car has 150k miles on it and looks like its been coated in oil and grime for a LONG time. Eventually going to swap in a carbed 350 but want to drive it with the tired 305 for a while longer but want to do it safely. If I wreck it I want it to be something else that causes it besides a stuck accelerator pedal!!
I searched and couldnt find anything close to this problem on here.
Thanks in advance for any info...

 

It is normal for the idle to go up when the AC is on. The fast idle solenoid on the carb is activated when you turn on the AC.

The auto-cruise is a separate problem altogether. I also have that weird auto-cruise problem. Sometimes it happens, and sometimes it doesn't. Seems pretty random but I have a feeling it is a vacuum problem. Do you have any cracked or broken vacuum hoses going to the carb? I finally found another person who has this same problem Let me know if you are able to fix this problem and how.

 

Welcome to the boards. As said above the A/C engages a solenoid that increases idle speed to compensate for the additional load. You'll see it in front on the driver's side. You can turn on the A/C with it idling to check its operation and adjust the plunger for proper idle with A/C on.

A good cleaning, though, is probably in order before making any adjustments. A can of carb cleaner liberally applied will do wonders on gummed up linkage. If the cruise control is causing problems the cable and linkage to it can be cleaned as well. Gunked up linkage can cause erratic operation.

Take care of your q-jet and associated controls. They'll swap over to a 350 and nearly tune themselves. If you need any help just ask.

 

Agreed with it being 2 separate issues. The A/C issue has already been covered. I'll take a stab at the other one.....

1. Worn out primary throttle shaft bushings. The cable and return spring arrangement is bad on most QJet-equipped cars. Both the throttle cable and the return spring are both pulling BACK on the throttle arm. Over tens of thousands of miles this causes the primary throttle shaft to eat into the metal surrounding it and the throttle gets "sticky" sometimes, often coming off of a full throttle run, but not always. Note this compounded by the vacuum pulling down on the throttle plates when the motor is running. Often it will move freely with the engine turned off but get sticky when the motor is running and pulling vacuum.

2. Choke not getting all the way open. The choke linkage has a fast idle cam built into it that raises the idle speed when it is engaged. If the choke isn't getting fully open (electric choke heater element on the passenger side of the carb weak, dead or not being supplied a full 12V of current by the wire that plugs onto it OR the linkage behind it being gummed up or mechanically damaged/mis-adjusted) it will cause a high idle sometimes. I doubt it would ever be so bad as to act like "cruise control" on the open road but it's something to check out.

Those are the only two things I can think of right off hand that would act as you describe.

 

Thanks for the welcome and info. Ill post a bio and pics of the bird when I can find the cord for the digi cam! LOL!!
Anyways, back to the problem... The high idle with the AC on is reallllllly high, 18-2000 when coming off the interstate and wont drop til the AC is turned off. Im glad the hear that everything has been carb specific thats been mentioned on here. I found a guy in AR that sells the exact rebuilt carb for $250. Looks like he does great work, been a rebuilder for over 20 years. Its Mountainmanfuelsystems.com or something like that. I guess I will just buy that when its close to completion of the top. Give the linkage a soak in my neighbors parts washer and relube em when the new carb is ordered. Ill also start another message when the top work begins. Should be interesting to cut the windshield frame off, separate the t bar and graft on a new front frame section. More to come later on that though!
Steve Rhoads
84 Firebird S/E