76 280z high rpm

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IdahoCoug
Posts: 1
Joined: Mon Jun 08, 2020 2:34 pm
Car: 1976 Datsun 280Z
1977 Datsun 280Z 2+2
1993 Nissan 300ZX Turbo

76 280z high rpm

Postby IdahoCoug » Fri Jun 19, 2020 2:25 pm

Hi, I am new to this forum. I have a 1976 280Z and my problem is while driving and coming to a stop the idle stays high for a few seconds before coming back down to normal. Is this a problem with my AFM setting? Any help is appreciated?


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AZhitman
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Car: 72 240Z RB25, 63 Bluebird RHD, 63 NL320, 67 WRL411, 67 SPL311, 68 510 SR, 77 620 SR20, 89 Pao, 97 D21, 98 S14, 11 LS460L, 12 Titan 4x4.
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Re: 76 280z high rpm

Postby AZhitman » Fri Jun 19, 2020 8:57 pm

Welcome aboard, Idaho!

A few possibilities, in order of commonality:

1 - Throttle cable linkage binding. Easy to test, pop the hood, run engine (by hand) at 3-4k RPM for a few, then drop the linkage. See if it remains at high idle, and if so, try to manually decelerate it. If that's the fix, lube the cable and throttle linkage.

2 - AFM contact points can get funky and sticky. You may have to do a search on the process for cleaning them, it's been over a decade since I messed with one.

3 - On deceleration in the L28, manifold pressure surges and causes the RPM's to stay high. The factory installed a "Boost Controlled Deceleration Device" (BCDD). Allegedly, they have been known to fail. I have heard that some Z owners remove this piece completely with good results.

4 - Vacuum leak (although this should maintain consistent high idle, not just after stopping).

Keep us posted!


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