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2200 rpm at idle


Alan Caldwell

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Ok I love my Z but this is crazy. She's been running AWSOME but all of a sudden she won't idle below 2200 rpm. I've texted the sensors have great fuel pressure checked the fuel regulator and the cold start injector. Everything looks fine but yet she won't idle where she's supposed to. Anyone have a similar problem and knows how to help I'd appreciate it.

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Could be the Auxiliary Air Regulator (AAR) or the throttle shaft sticking due to PCV valve vapor residue (reference Humble's How to Restore book,page 194) . He says Nissan actually issued a Recall Bulletin and kits to fix it around 1977, rerouting the PCV hoses.

Pull a hose off one end of the AAR and look inside when the engine is warm. It should be closed. If not, it might be fixable with carb cleaner.

Pull up on the throttle when the idle is high and see if the idle drops. I had to hose the inside of my throttle body with carb cleaner and use some Scotchbrite where the blades came close to the body when I had a hanging throttle. It only stuck when it was warm though.

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Check the AAR when she was hot and it was closed. And no leaks from the bellows. If I disconnect the hose that goes to the PVC valve the rpms drop but if I plug the hose they shoot back up PVC valve was replaced last month and it has suction when the car is running.

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Isn't 2200 RPM about where the TPS goes off idle contact to wide open contact? Maybe you got that wet or something? The adjusting 10MM bolt maybe loose? What about if you pull the gas pedal up with your foot?, will it go down? A spring on your throttle linkage may have come off. Is your BCDD still on? Mine was out of adjustment when I bought it and would hang on a high RPM for a few seconds then fall back down. Another thing Wick Humble mentions on page 194 is the connections between the EGR and the intake come uncoupled and cause a huge vacuum leak on '77's, mine did it and rotted out a hole in the aluminium intake. Take a mirror and look under the intake to see if anything looks peculiar, at the back, around #6. Maybe the wire spark arrester in your PCV hose off the valve cover is mucked up? Good luck.

A new game to play, how many blue words can you get in a post?

Edited by siteunseen
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After replacing a butt load of parts and all vacuum line she still won't idle worth a crap. Then after going on line and finding out what each component does and how the work I tapes the hole up for the BCDD and now she idling down to 850 so thinking that been the problem all along. So where the heck do I find new parts for it or can I just take it off all together

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Forgot about that part. Good detective work. According to the FSM, the BCDD is not repairable and has to be replaced as a unit. Many people remove it, but I think it helps with the gas smell on deceleration so the car might smell a little more if you do.

You might try running carb cleaner through the various passages, it might just be stuck. There's some springs, and a diaphragm and several passages inside. The diagram is in the Emissions chapter of the FSM, along with troubleshooting. Any year from 75-79, I think they're the same. There is also a solenoid inside, but I can't remember what happens if it loses power. Power is controlled by a speed sensor on the speedometer, through the black wire on the bottom of the BCDD. You might check that, maybe the power is stuck on or off.

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