Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Q-Jet 17057274 idles too fast
Schurkey:
What's the ignition timing at idle? Vacuum advance connected to manifold or ported vacuum?
beertracker:
Distributor advance is connected to ported (above throttle plates) vacuum. I will have to check on ignition timing. Could a bad EGR valve cause this problem? I haven't changed the EGR but the ball shakes freely.
BT
beertracker:
I just noticed the primary throttle plates have two V cuts in the outer edge of the plate. I am wondering is this factory correct or did some one take a triangle file to the plate. The cuts about 1\16" deep will allow air to pass even at closed throttle.
BT
Schurkey:
--- Quote from: beertracker on May 28, 2010, 11:44:13 AM ---Distributor advance is connected to ported (above throttle plates) vacuum. I will have to check on ignition timing. Could a bad EGR valve cause this problem? I haven't changed the EGR but the ball shakes freely.
BT
--- End quote ---
Sounds like you're describing the PCV valve, not the EGR valve. Yes, a defective PCV could cause a large vacuum leak that results in fast idle.
Having the throttle blades modified by cutting/drilling is probably the underlying problem, though.
omaha:
Hello,(I ve been MIA for a while but now I am back)
I agree with Cliff, air is bypassing the throttle somewhere. Be it at the PCV or the throttle base plate [warped or shafts worn]. Also make sure the distributor is not advanced too much at idle and uses the correct vac source. (sounds like you got that covered). Bypass air [in the form of passages in the carb body or drilled/notched throttle plates] is only needed when adjusting the throttle plate opening does not suffice. Throttle plates should not need to be opened more than .040 of the transfer slot exposed.
More than this will cause the dreaded nozzle drip. Make sure choke or fast idle mechanism is not hanging up or incorrectly adjusted. It does not take too much air woth the q jet to vary the idle (mine idles a bit too high sometimes but I know it is because of air leaking by the shafts.)
A stock Pontiac should be able to idle at 800 and maybe even less.
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