Idle speed dips after letting off gas - 92 civic d15b7

Hello All,
I have something on my mind that keeps bothering me and so far I could
not find an answer for it. I figured I'd post it and see if I could
get some ideas regarding this.

I have a 92 civic CX (canadian model with D15B7)with 300,000 km.
Car has been running fine, except for the overheating issue I had with
it when engine was under heavy load. I've replaced the head gasket,
got the head machined and pressure tested, flushed rad and cooling
system and that has taken care of overheating.

Ever since this has been done, I've been having an intermittent problem
where if I rev the engine and then abruptly let go of the gas so that
the throttle closes abruptly (while driving or at idle, in neutral or
with clutch depressed, does not matter), idle RPM will drop below 500,
making it sound like it's trying to stall. It will struggle at this
RPM for about 5 sec and return back to normal Idle of about 650 RPM
where it runs just fine. It keeps doing this even after the car has
warmed up.

Engine by itself runs just fine at other rpm, there are no signs of it
missing.

I've got few things I am going to check within the next couple of days,
such as timing belt tension, ignition timing, disconnecting air intake
pipe, etc. I am just curious if you guys have any other ideas or
suggestions about what I can try to do or possibly try to eliminate
some of the possibilites.

I would greatly appreciat some input on this.
Thank You and Best Regards,
BRadley

"Bob Radley (nazarl at idirect dot com)" > wrote in
oups.com:



> where if I rev the engine and then abruptly let go of the gas so that
> the throttle closes abruptly (while driving or at idle, in neutral or
> with clutch depressed, does not matter), idle RPM will drop below 500,
> making it sound like it's trying to stall. It will struggle at this
> RPM for about 5 sec and return back to normal Idle of about 650 RPM
> where it runs just fine. It keeps doing this even after the car has
> warmed up.



Shouldn't you be idling at 750rpm?

Turn off all accessories. Unplug the electrical connector to the EACV
behind the intake plenum. Drive the car. Is there any difference in
behavior? (Check Engine ight will come on. Don't worry about that.)

If there is a dramatic difference with the EACV unplugged, warm the car up,
adjust the idle screw to achieve 750 rpm, then plug the EACV back in.

When was the last time the throttle body was cleaned?




--
TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

"TeGGeR®" > wrote in
:


> Shouldn't you be idling at 750rpm?
>
> Turn off all accessories. Unplug the electrical connector to the EACV
> behind the intake plenum. Drive the car. Is there any difference in
> behavior? (Check Engine ight will come on. Don't worry about that.)
>
> If there is a dramatic difference with the EACV unplugged, warm the
> car up, adjust the idle screw to achieve 750 rpm,


Agh, agh, agh, serious error. Should be "to achieve *650* rpm".



> then plug the EACV
> back in.


That part is correct.


>
> When was the last time the throttle body was cleaned?
>


So is this one.


--
TeGGeR®

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

Bob Radley (nazarl at idirect dot com) wrote:
> I've got few things I am going to check within the next couple of days,
> such as timing belt tension, ignition timing, disconnecting air intake
> pipe, etc. I am just curious if you guys have any other ideas or
> suggestions about what I can try to do or possibly try to eliminate
> some of the possibilites.
>
> I would greatly appreciat some input on this.

how bout the O2 sensor? is it original?