RPMs fluctuating at startup???

Sometimes when i startup my 1994 Civic EX (vtec) the engine revs back and forth
between 1500 and 2000 rpm a few times before finally settling down at 1500
(then dropping lower as the engine warms up).

anyone know what might be causing this?

 

Electronic air control valve (EACV) (idle air control valve IACV on 92-95
Civics) passages may be clogged or have insufficient cooling. Remove, inspect,
re-install. Then thoroughly purge cooling system, letting the radiator fan come
on two times (may take 35 minutes or more for the fan to come on). Insufficient
purging led to my EACV on my 91 Civic having probably no flow through it this
past summer and having irregular idling. I took the EACV off, saw its empty
cooling line, and purged the cooling system thoroughly. Great improvement
resulted.

See www.autozone.com 's free repair guides for specific info about the IACV on
your 1994 Civic VTEC. Go to emission controls, diagnostic charts, then Idle
Control System, 1992-1995. Note that the second symptom listed is "When cold
fast idle out of spec (1000 to 2000 RPM)." It lists possible causes to be
1. Fast Idle Thermo Valve
2. IACV
3. Idle adjusting screw

Or the oxygen sensor could be going bad, but the oxygen sensor isn't supposed to
have much input until the car is warmed up, so I'd check the IACV first.

Or other, but the IACV does come up here from time to time as a minor problem.

 

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How full is the rad, and how full is the reservoir? Ever bled the air
out of the cooling system at the nipple? It may even be described in
your owner's Manual.

'Curly'

 

One of the sensors going bad.. forget which O2 ?. '92 and 98 Accords did it after
sitting unused for a month. About a 2000rpm swing even after warmup.

 

The O2 is ignored by the computer right after startup.