Why does my car drive itself when engine is cold?


#1

87 Accord. This thing has a carburetor. Maybe I just answered my own question. Is it because the cold engine idles at 2500 rpm ? On the way to work I can drive for miles at 50 mph in 5th with my foot off the gas.


#2

It sounds like the high idle adjustment is too high, 1000 rpm would be more appropriate.


#3

Carb needs a good cleaning and adjustment. The idle should be no more than 1200 rpm when warming up.


#4

Does it go up to 2500 immediately when you start it, or does it start out at 1200 or so and creep up to 2500?

It might just be that the weather’s getting warm enough that the engine’s warming up before the choke on this thing opens fully and the high idle disengages. If the carb’s still at high idle, but the engine is warm, it will idle really fast, like you describe. If your carb is working correctly, you should be able to “kick down” the idle by tapping the gas for a second. This is one of the many ways that an older car requires the driver to be a little more involved.


#5

Dies it ever idle correctly or at slow idle, ie ~900RPM?. If not, I might suspect a sticking cable or throttle flap.

If only when cold, I might suspect a slow to respond temp-Vacuum valve that controls the Choke Pull off diaphram.
Some older cars had Idle-up bypasses, which allowed the car to run faster when the AC or the Power steering was required at idle. These usually have solenoids, and it may be stuck open, expecially if it is running hi all teh time. hot or cold.


#6

I used to have a carbureted Accord of this same model year (or was it '88? Whatever), and this is simply how it warms itself up. Bumping the pedal and revving it for a moment will make it drop down to a more normal idle speed.


#7

It goes up to 2500 right when I start it, then it drops down to about 1200 and runs like hell, then creeps up to 2500 and runs smooth. Actually it’s only a problem when the engine has been running at normal temp and then shut off and allowed to sit for 10-15 minutes. When I start it back up and take off the idle will stay at 3000 RPM (remember, warmed up engine) for several minutes at which point even taching the engine won’t drop it back down.


#8

Yes, it idles smoothly around 900-1000 when the engine is nice and warmed up.