93 Accord idle speed

My 1993 Accord has started oscillating between 900 rpm and 1600 rpm
when warm and in neutral or park. In gear it idles smoothly at around
950. In neutral the engine revs up to 1600, drops suddenly, seems to
almost stall, then revs up again.

I just had the car in for 150,000 mile service. The shop replaced the
plugs, rotor, air filter, and fuel filter and a couple of oil seals as
well as some mechanical problems not related to the engine. They did
not replace the PCV valve, which would be my first guess, but I
checked it and it seems to be okay. They did replace the PCV valve
hose, but I do not know why. They did not charge me for it or mark it
on the invoice. Maybe it was leaking.

This is the four cylinder, 2.2 L fuel injected engine with automatic
transmission, USA version and USA emissions equipment.

Any suggestions will be appreciated and acknowledged. I want to know
if I can blame the shop before I take it back.


Elliot Richmond
Freelance Science Writer and Editor

 

Sorry I can't help, but I'm having same problem (intermittent) with my 95
Accord (Cdn version, but same size motor, etc). Please let me know if you
get any informative responses...

 

Has anyone monkeyed with the cooling system recently? Such that air may have got
in?

Make sure the level in the cooling system reservoir is correct. Then consider
doing a careful purge of air from the cooling system. See www.autozone.com for
free repair guides specific to your car. Make sure the fan comes on twice, as
the directions usually say. This may take 40 minutes or more with the car
idling.

My 91 Civic's cooling system had air in it, and I believe it was messing up the
EAC valve (a.k.a. idle air control valve). This valve has a coolant port which
was running empty on my car. I had symptoms like yours (though my car is a
manual transmission), and ultimately, the air purge fixed it right up.

How old is the PCV valve? I doubt this is the problem, but for the record, the
springs on these do wear. They may open and shut fine, but not throttle
correctly. If yours is the original, replace it. I'm changing mine at least
every 60k miles now. (The original made it to 140k miles without ever being
checked. I replaced it on a whim and my fuel mileage shot up over 10+% and has
stayed there.)

 

It's possible. I will check at the cooling system and replace the PCV
valve.

Thanks for the suggestions.


Elliot Richmond
Freelance Science Writer and Editor