Fast Idle Seems to be Delayed at Startup

[whit2887]

I have an 89 Accord with carb and manual trans. Each morning it starts up, then idles rough for 2-3 minutes at about 1000 rpm. During this 2-3 minute period the engine warms up (but not enough for the temperature gauge to move) and then the rpms steadily rise to about 2500. At this point the fast idle steps down like normal until it drops to just under 1000 rpm. The car runs smoothly on fast idle and afterwards. After warming up, the idle is smooth and the car runs fine with no obvious problems. It seems as if the fast idle process is delayed 2-3 minutes after startup. This "delay" happened when the temperature was below 20F and has also happened with the temperature in the 50s. I have searched for vacuum leaks by spraying carb cleaner on vacuum hoses and connections in the vicinity of the carb and I haven't found anything. Any ideas or suggestions for further tests that I can try?

[skycam_313]

spray the crap out of the choke assembly and wiggle it around.... its probably all crudded up.



happened to me.



when was the last rebuild of the carb?

[Jasonf860]

Have you checked out your choke pull-off? Mine had similar symptoms caused by the pull off not working.

[Toneloc5145]

My car just started doing this too. I found a couple of corrupted hoses that i fixed, but it still did it this morning. I'm going to try messing with the choke. But I think whatever causes my car to do this is also causing the engine to run a little rough even when it is warmed up. Its not apparent in the car, but if i look at the engine, you can tell that its not running smoothly.

[whit2887]

My Choke pull-off appears to work. I can watch it slowly open the choke as the car heats up. The choke goes from closed to fully open at operating temperature. I am suspicious of the fast idle unloader or possibly one of the thermovalves. If I can locate a vacuum pump I will try to test the pull-off and unloader. I have looked for linkage binding and I have sprayed carb cleaner over all the moving parts. It's warming up where I live and I may not be able to test this cold start problem for much longer. After a minute or so of rough idle in the morning it goes through the fast idle step down and I have to wait until the next day to get cold start conditions again.

[A20A1]

You might want to check the thermovalve.

Make sure the EFE screen is working, you don't want your carb pooping icycles in the cold.
Also make sure the hot air door is bringing in hot air.

[whit2887]

This morning I checked the thermovalves. No vacuum at startup on either valve A or B. The car idled rough at about 1000 rpm for a few minutes and then began to fast idle. After fast idle for a few minutes the engine warmed up enough to see vacuum from both thermovalves. When I reconnected the vacuum tubes I could see the choke pull off moving and the choke was fully open. I did not touch the throttle during this test. After reconnecting the vacuum tubing the car continued to run at fast idle, it seems that the fast idle unloader may not be working because the idle speed didn't automatically drop once the car was fully warmed up. Idle speed did drop after pushing on the accelerator pedal. As usual, after warmup the car idles smooth and runs fine. As I understand it, the fast idle unloader doesn't operate until it gets vacuum from the thermovalve, so I don't see how it could cause the initial rough idle even if it doesn't work. I think the next step is to get a look at the fast idle cam. I need to take the choke heater plate off to see inside. The "screws" look more like rivets to me. The manual says to take the "screws" out to get the plate off. Does this mean drill them out? Any other suggestions?

[A20A1]

yes, mark the position of the electric choke first though before you drill the rivits out.

I have a different way which involes taking 2 screws off and the 3rd one I snap off. It works fine but if you want to do it the right way then drill the rivits.

[whit2887]

I noticed that the exhaust was black while the engine was rough idling this morning. I guess there is not enough air, so I'm wondering about the choke pull-off again. The thermovalve to the choke pull-off seems to be working, but the manual says that there is a vacuum port that goes to the carb. Is that supposed to open the choke at startup? Is there any way to check it or clean it out?

[A20A1]

the choke opener has an internal vacuum port where it gets vacuum from, it's near the lower bolt on the choke opener.

[whit2887]

Is there some way to test the choke heater? It is getting 12V but I'm not sure it is working properly. What should happen if you disconnect the vacuum from the choke pull off? Will the choke heater open the choke all the way on its own? Can you test the resistance of the bimetallic coil?