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I’m having a problem with the warm idle. When the car is operating temperature the idle drops below 800 rpms and starts to shake when I’m in park and drive no matter if I’m at a stop sign or just sitting in the driveway. I have tried to raise the idle with the throttle stop screw but it always drops back down when I start the car in the morning. I can’t find any vacuum leaks, choke and throttle cable are good. How do I get the idle to stay at 800 rpms? Does It have anything to do with adjusting the throttle control valve/dashpot?
I also need to know if turning the dashpot screw clockwise raises or lowers the idle? I know it has something to do with the vacuum but don’t know if more vacuum means it lowers or raises the idle.
86 honda accord lx, 2.0L, 2bbl Keihin carb, 4 spd auto, 4 dr
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Does your carb have the automatic choke opener (most did)? When warm, is the choke fully open (fully vertical)? If not, and you have the automatic opener, the diaphragm has probably failed.
Has the car been tuned up in recent memory?
If not, that would be a very good place to start.
Change the spark plugs, air filter, gas filter and pcv valve with good quality parts.
Next, adjust the ignition timing.
After that, adjust the carburetor according to the procedures found here:
http://www.autozone.com/repairguides/Honda-Accord-Prelude-1984-1995-Repair-Guide/IDLE-SPEED-AND-MIXTURE-ADJUSTMENTS/Air-Fuel-Mixture/_/P-0900c152800b807cIf the link is not permissible just Google 86 accord carburetor adjustments autozone and you should find it.
cap269 and Bonnieman
cap269 yes I do have a automatic choke and yes it’s vertical. My carb is new rebuilt one so it’s not a failing diaphragm.
Bonnieman as a matter of fact I just went for a smog test so all of those things were done on the car. Will try what autozone has said to do.
Thanks guys
You didn’t mention that it was a new carb in your original post, so I assumed it was the original. Was the new carb properly adjusted after it was installed? All carbs need to be set up and tuned after installation. Rarely will a carb bolted on just out of the box work properly. There are different air passages for cold and warm operation. You may want to reference the information found here: http://www.aa1car.com/library/carburetor_honda_keihin.htm
Sorry I didn’t mention the new carb. The car was adjusted by a mechanic but he didn’t do it right. I was having a problem with the fast idle too, it was going up to 3000 rpms and wouldn’t come down on its own until I hit the pedal then it would drop to 1500 rpms and stay there. I posted on several forms with pics and no one could answer my quetion about the adjustment screw. I finally found out where the adjustment screw was on my own because no one on any forum could answer a simple question was this the screw. I brought down the fast idle but it still doesn’t kick down on it’s own. But that’s another issue.
Right now I’m trying to find out what the throttle control/dashpot screw does. I read it has something to do with how much vacuum it applies to the idle but doesn’t explain which way to turn the screw. I just need to know if turning it clockwise will raise or lower the idle.
I’m trying to make the idle stable when the car is in park or at a stop signal. I’ve tried to adjust the idle with the throttle stop screw but the idle always ends up dropping down the next day like I didn’t do anything to it.
[quote=”buddy1″ post=186719]Right now I’m trying to find out what the throttle control/dashpot screw does. I read it has something to do with how much vacuum it applies to the idle but doesn’t explain which way to turn the screw. I just need to know if turning it clockwise will raise or lower the idle. [/quote]
The dashpot helps control the rate at which the throttle closes during deceleration. It won’t affect idle in any significant way. Adjusting the diaphragm screw controls the amount of physical resistance on the diaphragm thus allowing for a faster or slower closure of the throttle. It works in combination with the other throttle controls on the carburetor to help reduce emissions.Side note, in thinking about it and recalling when I had a ’79 CVCC, the curb idle speed you want seems a bit high. What does your under-hood sticker say the idle should be? I seem to recall my car wanted 550-650. Another reason your idle may not be staying changed is because your 86 has a computer control over the idle to maintain its configured idle speed. You may be working at cross-purposes with this computer and it is compensating for your adjustment. If you cannot operate the engine at a lower (spec’d) rpm due to shaking, then perhaps your engine mount(s) have cracked and need replacement.
Your base idle speed has to be done on a fully warmed up engine and those specs should be listed on the underhood sticker.
There is also an AC idle speed to bring the idle up whenever the defroster or AC are running.In a high mileage engine, there may be some roughness to the idle due to wear, vacuum leak(s) or bad motor mount(s).
Your vacuum leak may not be an obvious one.
A sticky PCV valve (pinch the hose and, if the idle smooths out, change the PCV valve) or a leaking brake vacuum booster (again, pinch the hoseoff to see if idle smooths or intake manifold gasket leaks are less obvious but just as detrimental.
A sticking EGR valve will also be a less than apparent vacuum leak.
Not sure if Hondas are picky and must have a genuine Honda brand PCV or not.You mention the idle speed being too low in the AM when the car is first started.
No idea what your experience is with carbureted engines, so I wondered if you’re aware that carbureted cars require that you fully depress and release the gas pedal before starting in order to engage the fast idle cam.
By design, the fast idle will not disengage until after the throttle is moved/gas pedal is depressed.
2000-3000 RPMs at startup is the range for the fast idle speed.
It will then drop in 500RPM increments until it is off the fast idle and onto the idle circuit.
This relies upon a good working electric choke and a working thermal vacuum valve, as well as a proper fast idle adjustment.Assuming your mechanic adjusted the idle mixture screws properly, there’s an easier to follow link (than the idle mix link) for the base idle speed adjustments.
There are many adjustment screws on these carbs, so you have to be absolutely sure you’re turning the right one beforehand.
It’s the one closer to the firewall with a plastic cap/knob on it.
Since the quality of a rebuilt carburetor depends on the rebuilder, know that a bent idle speed screw will wreak havoc with the idle circuit.This page details the exact procedures for idle adjustments but you must follow them to a T.
http://www.autozone.com/repairguides/Honda-Accord-Prelude-1984-1995-Repair-Guide/IDLE-SPEED-AND-MIXTURE-ADJUSTMENTS/Idle-Speed/_/P-0900c1528005f388
When it states that the upper vacuum hose of the idle control solenoid valve has to be disconnected and plugged before adjusting the idle speed screw, then you must do it that way.
Don’t forget to adjust the AC idle speed, assuming your car has air conditioning.quick question on that reply about adjusting the ac idle. thats what im having the world in frustration.
i believe its the one next to the accelerator pump. but mine is vacum operated, it doesnt have the adjustment screw on top the unit ????
i have seen them on other models but i cant seem to figure out how to increase ac idle speed.. please help !
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