76 280z high rpm

A forum for owners of S30 and S130 Datsun Z's... 240Z, 260Z, 280Z and 280ZX!
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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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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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