strange intermittent high idle

[Strugglebucket]

okay, here we go: '88 dx, automatic, kl (CA) emissions.

start it up, and it runs at about 2.5k at first and gradually rises to somewhere between 3 and 4k. it will stay that way sometimes all day, sometimes it will drop to normal idle after 10 or 15 minutes. sometimes it will drop to normal idle immediately after i start it (even cold). when, or if, the idle does drop it is always a sudden and immediate drop. once the car is idling normal it will stay that way as long as it's running. if i shut it off for a few minutes (while it's idling normal) and then start it again it will rev up to 3something k and after maybe 5 seconds drop back down to normal.

any ideas? the car runs fine when it finally idles down. lately it's been stuck high most of the time and it makes it kind of hard to drive.

[A20A1]

Check your coolant level... and make sure it is flowing and it doesn't have air bubbles.

Other then coolant it could be a sticky linkage on the fast idle or electric choke or broken choke.

[Strugglebucket]

the coolant is fine, new thermostat and i bled the heck out of it just to be sure.

i actually tried removing the choke plate once and it would always idle high. then about a month later i put it back and afterwards it went back to working sometimes being in california with a stock honda carb sucks.

[DanG86LX]

..i actually tried removing the choke plate once and it would always idle high..

did u remove also the choke housing with electrical choke, 3 long screws ?
If u did then something else is pulling ur throttle like:
throttle controller
(A/C) idle boost solenoid valve
or sticky throttle flap

[Strugglebucket]

all i removed was the plate.

i know there are a few different things that could be causing my problem; i'm just having trouble troubleshooting it. everytime i look at those system to sub-system diagrams in the shop manual i just get a headache

[A20A1]

I suggest warming up your car, wait for the fans to come on a few times, or if they don't at least wait 10 minuets or so, depending on where you live.

Then start turning out idle adjustment screws to ruel out their involvement in your high idle problem. The main scre to hold idle will be your throttle stop... I'd set that to your best lowest idle speed, preferably 800 or below, but some cars may need it higher. But this is with vacuum advance hooked up so maybe you can adjust it a little higher if you need to.

https://www.3geez.com/showthread.php?t=44074


thats the order I adjust the screws.


.
.
.

[A20A1]

the coolant is fine, new thermostat and i bled the heck out of it just to be sure.

i actually tried removing the choke plate once and it would always idle high. then about a month later i put it back and afterwards it went back to working sometimes being in california with a stock honda carb sucks.

Make sure your throttle cable is removed so you know it isn't pulling on your throttle. You may have too much opening in your throttle, try and lower it.... the fast idle screw when cold... but all other screws when the car is fully warm.

A vacuum leak can cause your thottle controler/idle diaphragm to open the throttle.

.
.
.

[Strugglebucket]

Make sure your throttle cable is removed so you know it isn't pulling on your throttle. You may have too much opening in your throttle, try and lower it.... the fast idle screw when cold... but all other screws when the car is fully warm.

A vacuum leak can cause your thottle controler/idle diaphragm to open the throttle.

.
.
.

when it's idling high the only screw that has any effect is the throttle stop screw. i could bring the idle down with that, but then if whatever's wrong kicked back to normal operation the engine would die.

[A20A1]

So it's idling high when warm.
I suggest you turn out the throttle stop to lower the idle, what ever is wrong may go away, but here are some things to check before hand.

There are SIX likely ways you'd get high idle without it being the throttle stop screw

• If the idle diaphragm was opening the throttle because of bad adjustment or vacuum problems
• .
• If your vacuum advance #25 was getting vacuum when it shouldn't because of thermovalve problems
• .
• If the fast idle isn't disengaging because of a linkage or adjsutment problem
• .
• If the throttle plate or linkage is getting stuck
• .
• If the throttle cable is getting stuck
• .
• If your distributor body turned or was set out of the correct timing

There is ONE other way you'd get high idle without it being the throttle stop

• If the fuel mixture was artificially rich and a vacuum leak acted as throttle giving an appropriate amount of air.

Setting ignition timing is independent of engine rpm, as long as you disable the vacuum advance and use the appropriate markings to set the base timing. So double check that if you can.

So anyways, if what I listed is not your problem then I suggest you turn out your throttle stop screw and lower the idle.

Cars idle better when on the idle circuit... too wide a throttle opening and you get off the idle circuit causing poor idle... too narrow a throttle opening and not enough air gets in for the motor to run.

.
.
.
.