1986 Honda Accord changing idle speed

I have a 1986 Honda Accord Lxi we bought new. It only has about 120K on the odometer. Recently, the idle speed jumps up about 500 rpm AFTER the engine reaches operating temperature. The PGMFI light on the dash comes on at the same time. The dealer can’t diagnose the problem. I have a new tuneup, new EGR valve, and no air in the cooling system. I am thinking maybe the idle control solenoid is bad. Anyone with the same problem or suggestions??

Assuming you’ve checked carefully for vacuum leaks and split vacuum lines & hoses (and this car has lots of vacuum lines), it very well might be the idle air control circuit. Been awhile since I’ve worked on an old Honda of that vintage, but as I recall the Idle Air Control Valve / Solenoid is mounted on the firewall, with wiring and vacuum lines running to it, and 4 screws holding on an o-ringed square plate on top of the body of the unit. If you remove the cap and look inside you’ll see a large metal “screw” with a wide slot; tighten that by hand with the biggest straight screwdriver you have and then reassemble. If that doesn’t cure your problem, you’ll need a new solenoid. Good luck!

I have this exact same car and the idle control is constantly driving me nuts. First and foremost, turn the key to “run” and look under the backside of the driver’s seat. You’ll see a little plastic box with a little plastic square on it. This is the computer, and when you pry off the little square, you’ll see a red light that flashes the trouble codes at you. It’ll flash the first digit of the code then the second, for example 1 flash, then a pause, followed by 4 flashes would mean code 14, which is an IAC fault. Look up the codes here: http://www.troublecodes.net/honda/hondadtc.shtml

Most likely, though, you’ll be getting a code 14 which means that the computer isn’t able to adequately control the idle speed. This MAY mean it is the IAC valve is faulty, but there are other possibilities.

There’s two devices that control the idle in this car that Sean01 seems to have combined in his recollection. There’s the computer-controlled IAC valve that’s mounted over on the right hand side of the engine compartment and then there’s a separate thermally-controlled valve that’s mounted on the back side of the throttle body. I don’t believe there’s any adjustment that can be done to the computer controlled valve other than cleaning it, but the thermally controlled valves are very finicky and, in addition to causing erratic idling when there’s air in the coolant, require fairly frequent adjustment.

The thermal valve adjustment is at least pretty easy. With the engine warmed up, look for a flat metal piece with two screws holding it on near the back of the aluminum piece that says “12 valves”. Take the two screws off and remove the cover. At that point, you’ll be able to use a flat screwdriver to move the little pintle thing inside the valve until you get the correct idle speed. Then put the cover back on and you should be set.

If this doesn’t fix it, post back and we can go through various other possibilities if you’re mechanically ambitious. Otherwise, you should try to find an independent Honda or at least imported car specialist to take this to. The dealer can’t really help you because most of the dealer techs are too young to have worked on many cars with this particular FI system.

Thanks a lot for the info, I didn’t know about the computer diagnostic light. I’ll check this out and post back. Did you ever replace the computer controlled IAC valve on yours?

It’s not necessarily an idle speed problem. When the engine light comes on, for whatever reason, the system goes into “limp home” mode with a higher idle speed. My '88 Accord LXi had the same symptom and it turned out to be a problem in the EGR system. So first read the code like GreasyJack sez.

hey i was wonering if you got the problem fixed i am having a simular one but my idle keeps climbing when its warm.