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Old 08-18-2015, 08:23 PM   #1
1st Gear Newbie
Join Date: Jan 2014
Location: Indianapolis
Posts: 2
Post-interference rebuild, poor idle (non vacuum) - 'thoughts?

Folks, I'm at the end of my wrenching-skills, following a post-belt-break
valve-job. The vehicle is an E30'vert with the M20B25 (non-eta) engine.
I had a few valves break, and couple bent - I replaced bad ones
from a donor head, all were 'roll-tested' for straightness, dip cleaned
and polished - and finally lapped in-port upon re-installing. Yet;
I have a "lumpy" idle (made worse by removing the oil-fill cap
on the valve cover), so it certainly seems to be top end blow-by; BUT:

1) After doing compression test - all good/spec - I did a leak down...
A) All cylinders similar, under 5% loss on any one at TDC
B) No audible hiss from exhaust, throttle or in rad/coolant
C) However, EVERY cylinder had slight air hiss through vc's oil cap
- It was audible, but not enough to even wiggle tissue paper
2) When rebuilding the head/lapping valves, I cold-adjusted them to spec
A) Running, the valvetrain is quiet; no audible tapping or clicking
B) No other anomalies in running; pulls strong, no lagging or smoke
3) To try cylinder isolation, once plugs were reinstalled, did a plug-yank
A) Sequentially removing plug leads, tried to find "weak" cylinder
B) Spark removal equally degraded idle, irrespective of cylinder

It's official; I am out of ideas. Any next-step tests welcomed. I am
loathe to yank the cover with nothing apparent to look-for .
....'Thoughts? THANKS, EVERYONE
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