89 SE-i surging idle

[groundspeed]

I have a 1989 Accord SE-i M/T A20A3 motor. When warmed up and the car is stopped or at very slow speeds the engine surges between approx 1000 and 1500 rpm rythmically at about a 1 second period. I have seen other threads with same problem and have cleaned the IACV, and the fast idle control valve with no luck. If I unplug the electrical connector on the IACV the idle still surges but a smaller amount and about 1/2 second period. With both vacuum advance lines disconnected the surging stops. There is a vacuum line on the upper corner of the throttle body that goes into the control box on the fire wall, #21, if that is disconnected the idle surging stops and the idle drops very low and is a little rough. With this line disconnected, unplugging the IACV connector has no effect. There is plenty of coolant but it is old and I have not yet flushed the system. No codes are displayed. Does this sound like a vacuum leak or a bad IACV solenoid? Any help is appreciated.

[AccordB20A]

my guess is ur IACV works good. Have you played with your idle screw on the tb? maybe the idles too high. make sure your vacuum lines have no holes/are all connected. Another thing to do is make sure your fast idle valve is screwed down enough. to check it when the cars up to temperature and doing the idle thing take the lid off it and put your finger over the hole in the middle, if nothing happens the valves good as u have a vacuum leak issue somewhere else.

[groundspeed]

Fast idle valve checks good with your test. Moved the idle screw about 40 degrees in both directions but did not notice any change. I have looked pretty thoroughly and I cannot see any disconnected or broken/leaking vacuum lines but I agree it would seem to be a vacuum leak somewhere. Manifold gasket maybe?

[w261w261]

Did this just start? Did it arrive suddenly (did you get low on coolant and add some?) or develop over a period of time? You might try to open the bleed bolt to make sure there's no air in the system.

[groundspeed]

Did this just start? Did it arrive suddenly (did you get low on coolant and add some?) or develop over a period of time? You might try to open the bleed bolt to make sure there's no air in the system.

Started very suddenly. One day it was fine and the next day the idle started to surge. One other symptom is that before the engine warms up it idles faster than it did before the problem started. Haven't added coolant or done anything to the motor. I'll be gone for a few days. When I get back I will flush the coolant and make sure there is no air in the system. I did a little more trouble shooting and discovered that even with the vacuum advance lines pulled off I can make the idle surge by pulling off the vacuum line that goes from the plenum to the pressure regulator that is at the end of the fuel injector pipe.

[Dr_Snooz]

Manifold gasket maybe?

Yep. That would do it.

https://www.3geez.com/forum/showthrea...anifold+gasket

[Discovery]

Started very suddenly. One day it was fine and the next day the idle started to surge. One other symptom is that before the engine warms up it idles faster than it did before the problem started. Haven't added coolant or done anything to the motor. I'll be gone for a few days. When I get back I will flush the coolant and make sure there is no air in the system. I did a little more trouble shooting and discovered that even with the vacuum advance lines pulled off I can make the idle surge by pulling off the vacuum line that goes from the plenum to the pressure regulator that is at the end of the fuel injector pipe.

Check or replace line #21 for leaks. It feeds the MAP sensor in the black box from the intake manifold . MAP / Manifold Atmospheric Presure/ then check the intake manifold for leaks. Bad or leaky manifold makes the map sensor do creazy things.

[Demon1024]

check your vac advance diaphram
you said it stops if you remove them?

[groundspeed]

Both sides of the vacuum advance hold a vacuum. I cleaned the distributor stator so it moves freely. If I pull a vacuum on the vacuum advance manually the idle will surge although the vacuum stays steady. I can make the idle surge with both vacuum advance lines disconnected so I don't think it is the problem. When I get back in town in a few days I will check the #21 vacuum line for leaks and flush the radiator. Thanks to all for the suggestions. Keep them comming.

[-$MOKIN-]

what was the problem?