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Old 08-16-2014, 06:53 PM
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TOO High idle on 72 pontiac 400 w Qjet

I have a 1972 pontiac grand prix with a 400 ci engine & rochester Q jet. I am experiencing very high idle at 1500 and can't get it to come down any lower. I have checked all vacuum lines and the carborator base gasket. I did a check with liquid at intake mani bolts without finding any leaks. Oddly the distributor when tightened down makes it race more. Does this suggest an internal vacuum leak in intake mani or elsewhere? It seems to run hot with some quick heating of coolant. No oil in rad or water in oil. Any help from pontiac enthusiasts would be greatly appreciated! Thanks

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Old 08-16-2014, 06:56 PM
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Check the secondarys in the carb.They sometimes stick open just a tad and can cause a high Idle.
Also check the PCV valve.Put your finger over it to block its suction,it may be causing some issue as well.
Check that..post back.
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Old 08-16-2014, 08:59 PM
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secondarys look closed,pcv ok. vacuum at 22 steady, thanks
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Old 08-16-2014, 09:16 PM
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Quote:
Originally Posted by pontiacgprix View Post
secondarys look closed,pcv ok. vacuum at 22 steady, thanks
First, if you are looking at the air valves on top of the carb, those are NOT the secondary throttle plates, which are on the bottom of the carb. Even when closed, the air valves can pass enough air to raise the idle if the secondary THROTTLE PLATES are not fully closed. You need to open the air valves manually and look down into the secondaries to see the throttle plates. Do this with the engine off.

Personally, I doubt this is the problem. You didn't mention anything about the idle adjustment screw. I assume this is not the problem (and that you are adjusting the idle screw on the driver's side, not the fast idle screw on the passenger side). Verify that the choke linkage is adjusted correctly and that the fast idle cam is not holding the throttle open when the car is warmed up. Verify that the throttle plates are not hanging up on the base plate gasket. Verify that the idle kicker solenoid (if you have one) is not holding the throttle open.

Keep in mind that you are supposed to set the timing, lock down the distributor, and THEN adjust the idle speed. You may need to check and adjust it again if the idle was really high before. You are setting the timing with the vacuum advance plugged, right?
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Old 08-17-2014, 12:27 AM
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Yes, throttle plates below are closed and not binding on base gasket. Not the cams or linkage on left side or throttle adjustment screw on drivers side. Not the solonoid(equipped bur not engaged or activating)Yes, i'm timing when vacuum advance is plugged. Notes: Idle increases as distributor is tightened down. vacuum?/ Rapid coolant heating after running a few minutes.thanks again
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Old 08-17-2014, 08:36 AM
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Have you checked the timing?
Have you popped the dizzy cap off to check the weights and springs?
Could be stuck weights!
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Old 08-17-2014, 11:02 AM
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yes, i inspected springs and weights, I even swapped another working distributor from 2nd pontiac I have here. Same racing idle.
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Old 08-18-2014, 04:47 AM
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Check to see if high idle cam ("elephant ear") is sticking on the choke. It is probably hung up and not returning to the lowest step.
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