I picked up an 85 z28 with a 4bbl cc quadrajet. 80k original miles. 2gs thinking to my self what a steal. Straight body's slightly high idle thinking its going to be a quick fix I was wrong.
Now I'm at my wits end. Timmed it to 8 bdc an didn't fix the idle. Look for vacum leaks can't find any. Order a new carb from summit because my buddy took a look at the old one an said it was junk. Someone did a number on it. New carb on tightend the idle screw all the way in backed out three turns go to start it up an staight to 2k rpm constant. Any input?

 

Id say look harder for vacuum leaks. Did you use carb cleaner or propane to check for leaks? So if you back the idle screw out all the way it still idles at 2000 rmp?

 

during my search for vacuum leaks i happened break my coolant temp sensor an two other sensors that sit in the manifold. the emission sticker says they are t.v.s but im having no luck finding out what they are so i can go get replacement sensors an then im going to get some vaccum an start once more to finding leaks...the more i try the more i seem to break crap.

 

I'd be very wary of a "buddy" looking at a carb and calling it "junk".

What did you get as a replacement?

The most common reason for high idle with a q-jet is the throttle being held open. The most common cause for the throttle being held open is the choke not disengaging the high idle cam. The most common reasons for the choke not disengaging the high idle cam are inadequate voltage to the choke thermostat, a bad choke thermostat, or gummed up choke mechanism. Among other causes for the throttle being held open are improper adjustment, mechanical binding/interference, or interference with a gasket.

Advancing the base timing typically will raise the idle, not drop it. Assuming this is the base LG4 V8 (the information you provided was very sketchy), the base timing would be zero degrees. The less common L69 base timing is 6 degrees BTDC. Base timing is set with the flat 4-wire connector from the base of the distributor to the harness along the firewall disconnected.

It's been a couple of years since I looked, but I was able to get all of the TVS/sensors I needed from O'Reilly or Advance Auto.

 

Where the idle mixture screw are underneath was drilled to hell exposing holes at the base of the carb. I ordered a rebuilt replacement quadrajet from summit because I couldn't find any on island at an shop or junkyard. My chiltons said 8*bdc for the LG4 so I disconnected the connector an timed it to 8. Where it's at now is once turned on it idles at 2k constant idle vaccum is pulling a over 26 constant. Found the tvs sensors online went to the store an there are none on island so now I have to order them I'm going to recheck for vaccum leaks when I get a chance which isn't anytime soon due to the army and currently mid move to post. I will chech for voltage at the choke when I get a chance. I was under the impression that if the carb was tuned too lean it would cause it to compensate and run rich. This is my first carbd car. My last car was a 92 rs so it's a foreign language to me which I'm picking up quick but it's killen me trying to figure out why it's idling high

 

So I've got it down to the hot idle cam. The choke opens up an the levers on the side of the carb drop down. The hot idle cam doesn't want to disengage and I'm trying to figure out how to adjust it but to no luck the search button isn't helping. So anyone want to give me a quick run down on how to adjust the hot idle cam to disengage

 

8 degrees BTDC is the non-computer timing setting from the factory. LG4 with computer control is zero degrees base timing (at idle with the flat 4-wire connector disconnected). Timing advanced too far will cause high idle (among other problems).

There isn't any adjustment to disengage the fast idle cam, assuming the rest of the choke mechanism isn't FUBAR'd. See the factory diagram for the pieces involved: https://www.thirdgen.org/tech/images/e4me016.jpg (I haven't heard of 3rd gens with the rear vacuum break, item #48, usually only have the front vacuum break, item #25)

Try this: With the engine cold and not running, remove the air cleaner. Open the throttle a little. The choke butterfly should snap shut and the fast idle cam (the green weight thingy) should engage (weight comes up). If that happens, so far so good. Now, hold the throttle open a bit again, with your other hand open the choke butterfly completely. The green weight should drop down. Now let off the throttle while holding the choke butterfly completely open. The high idle adjustment screw should be disengaged from the high idle cam now (hard to see, but you should be able to jiggle the weight a little).

If it is disengaging the high idle cam when you do this manually, then repeat the process except let the engine run long enough to open the choke butterfly. This will likely take several minutes. Of course, to get the fast idle cam to disengage, you have to open the throttle a little to remove the force the adjustment screw is putting on the cam. If the choke butterfly doesn't open all the way after several minutes (I'd say give it at least 10), then you've got a problem with the electric choke thermostat.

Another way to check is to start the engine with the air cleaner off, and just push the weight down with your finger. If it doesn't lower the idle, there's something screwy.

Since you had the same problem with the original carb (at least, it sounds like you did), it's highly doubtful the carb is causing the problem.

BTW, some details beyond "it's junk" are usually helpful. What you described with the idle mixture screws doesn't sound fatal. You have to do that to some degree to get to them to remove the idle mixture screws during a rebuild for proper cleaning. Without pics, it's hard to say for sure, but unless there was a leak path from the intake opening to some carb circuit, or from a carb circuit to the outside (which doesn't seem possible without seeing it), it wouldn't be a problem. Since the problem didn't go away with another carb, again, doesn't sound like a carburetor problem.

For the record, what kind of gasket did you use with installing the replacement carb?