90 Accrd surging idle in park when warm

Hi folks,
This has only recently started to happen.. my car is a 1990 Accord
EX, Auto, with 178k on the clock. The only work I've performed on the
intake was to clean the EGR ports(about 5months ago), and routine
throttle-body cleaning.
This only happens after the car has been warmed up and out on the
highway. The rate of incident is increasing. After letting the car sit
and warm up(very cold in PA this time of year) for 15-20mins, idle is
fine, drives fine.

After driving, when I put the gear into park, the idle will jump
from 1000 to 1500rpm(will raise to 1500 over about two seconds, then
drop sharply to 1000, and repeat). Putting the car into
reverse,D4/3/2/1,or neutral returns the idle to normal.

It's almost like when I shift from Park to Reverse: the idle raises
for a second, presumably because the reverse gears are kicking in(???
this is just an educated guess ???).

The gear indicator *does* indicate it is in park. I have tried
shifting up/down through the gears while the engine is off to possibly
clean any bad contacts in the shifter unit. No good.

I have unbolted the pulsed-air valve(on the intake manifold, the one
with the small metal screen in it) and cleaned it with throttle-body
cleaner. I also inspected the cold-start air valve per service manual
directions(has the wax bi-metal and coolant lines in it to idle high
when cold). I took the top service cap off, noted the air flow while
cold, waited for car to warm up, and then observed no air flow(normal
operation).

Any ideas?

Thanks folks!
-Jamie

 

------------------------

First thing I'd check is the coolant level. Rad must be absolutely full,
and coolant reservoir full to the line, otherwise air in the system can
fool some sensors. Have you bled the air bubbles out recently? Idling
your Honda to warm it up does nothing but bad for it. Water and acid
by-products in the oil / intake. Can ice up and clog the PCV valve.
Check what the manual says about warm-up time.

'Curly'

 

Since the RPM surges when you go from P to reverse, I wonder if your
load sensor is bad. The load sensor is supposed to sense a change of
electrical load and adjust the idle accordingly.
In your case, the reverse light obviously is turned on and possibly
this is detected by the load sensor. Maybe your sensor is just too
sensitive and causes surging.
It could also be a vacuum leak somewhere.

Remco

 

Curly,
Thx for the response. No I havn't bleed the system lately. It's been
a year or so that I'v changed the fluid, so i suppose it's about time
anyways. I know how to bleed the coolant when refilling w/the bleeder
screw, but can the system be bled while it is at capacity? My brother
told me to run the car w/the rad. cap off untill the thermostat opens
and you see coolant flowing.

 

wrote in

Not usually necessary.

After you refill the system using the bleed screw (make sure the heater is
turned to FULL HOT), start the engine, then bounce the bumper and squeeze
the upper hose once in a while. The level will blip down as bubbles are
ejected.

Once it stops going down but keeps rising, put the cap back, make sure the
reservoir is full, then drive the car around until the temp gauge reads
full-hot.

 

Thanks for the info 'Teg... It'll be until next weekend that I get a
chance to replace my coolant, so I'll post back then.

Regards,
-Jamie