# High idle/low vacuum



## Max Blast (May 27, 2006)

Hi, first post here.

I've got a well used 1985 Nissan 720 Kingcab 4x4 Deluxe, 3rd owner with all receipts from 1985 on. It's completely stock and unmolested and will be a sweet dirt rig but it's doing some strange things:

-It's got very low vacuum. I measured 18 inhg (shows late igntion timing on gauge) when first starting up cold then about a minute later it drops to 6 (very low- shows late valve timing or manifold leak on gauge) Rock steady though.

-Extremely high idle. It idled at about 1500 when I got it, but would drop to the regular 800 only when restarting it warm. After I replaced the alternator it idles at 2000 warm or cold and I did not even touch the carb, and will not drop. Is there an alternator/carb connection? My Haynes says there is. The idle will drop to about 1500 for a few secs when manually goosing the throttle linkage but then surge right back up to 2000. I've checkd the linkage and there's no binding. Also checked carb electrical connections, seem secure with no wire fraying.

-I've also checked for vacuum leaks with starter fluid and gone over hoses....nothing. Timing is also set to stock, new plugs, wires and caps.
Carb float level stays put at half as seen thru sight glass.

-It drives just fine (well they were slugs even when new) except for the high idle and dieseling on shutoff due to high idle.

Where else should I look?

Thanks,

Max


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## usmyrmss (Oct 31, 2006)

Max,

Did you ever get any feedback on this. I have the same truck. Original owner. Same problems. Done the same troubleshooting. Now it's cutting out under load at 3000+ RPM. Seems lilke a vacuum leak or an electrical component breakdown at higher RPM. I'm not sure which.


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## mech361 (Jul 31, 2006)

If these are fairly high mileage vehicles and have not been driven very hard in the past, it's possible that the secondary in the carb may be stuck partially open. This would cause the high idle, and low vacuum reading. (without a dead skip I might add.) USMYRMSS, sounds as if you have a problem in your distributor as well. Have a good look at your rotor for burn through as well as the cap. A word of advice, if you have a problem with you cap or rotor get geniune Nissan parts to replace them with.


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## usmyrmss (Oct 31, 2006)

I replaced the fuel filter last night. Voila!!!!

http://www.nissanforums.com/images/smilies/bubbarubb.gif
:woowoo:


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