Sudden high idle, rough idle, gas smell, very poor mileage

1985 Accord. 172k miles. Carburetor. Manual transmission.
Air cleaner recently disturbed to explore occasional carb icing problem.
(See http://www.misterfixit.com/carbice.htm)

Engine has been running well. **Suddenly** I have a high idle problem. Near
the end of a 20 mile drive on a recent cold day, stopped at a light,
suddenly the engine wouldn't idle down. Idling at 2K or more. I let out the
clutch and the car almost drives itself - little accelerator required. I've
not seen idle below 1.5K since. Runs rough, gas smell, and gas consumption
is off the charts. On cold start, idle immediately jumps to 2.5K or more
before idling back to about 1.5K. Fast deceleration or sharp left turn (!)
seems to cause idle fluctuation.

Why?

Thanks
Richard D.

 

Sounds like a vacuum leak to me. Recheck your hoses or perhaps one of your
hoses was hard and brittle and when moved it cracked.

CaptainKrunch

 

Is there gas coming out of the float bowl vents? Sounds like a float that
has sunk.

Pull the air cleaner cover & peek inside the carb with the engine running.

How much corrosion is there on the wiring in the engine compartment?

 

you can first try to turn the idle down, there should be a knob on the
back of the carb towards the passenger side, i believe that counter
clockwise will turn the idle down. there may still be a vaccume leak in
which case this bay only be a temporary fix
Andrew

 

Thanks Cap'n.. I'm a newbie, so please forgive the ignorance I'm about to
display.

I just sprayed for vacuum leaks. There is a small "black box" attached to
the rear of the air cleaner. The only idle drop I hear is when I spray
around that box. What is it? Should it be replaced? Is this my problem?

I've also heard that EGR or PCV valves might be culprits. Is that consistent
with the sudden onset of this problem? What do these valves look like and
where are they?

Thanks
Richard D.

 

Thanks, Tegger.

Is sunken float consistent with the sudden onset of the problem?

Please forgive my ignorance. When peeking inside the carb, what should I
look for?

I think wiring looks pretty good.

Thanks,
Richard

 

An update:

Engine also diesels (run on) for a few moments after shutdown. Never seen
that in cold weather before.

Light colored smoke for a few moments on startup in cool/cold weather has
been an issue for a couple of years. Since the high idle began, there is
much more smoke for much longer time (several minutes).

While out driving this morning there was an interval of several miles where
idle dropped and the engine stalled several times. High idle soon returned.

Thanks for any available insight!
Richard D.

 

"Sudden onset"? I don't know. Maybe not. Seems to me a leaking float would
gradually cause problems.

There *is* another possibility I just thought of: The choke plate.

With the engine fully-warm, the choke plate should be fully open, standing
vertically. Is it? The choke plate is at the very top of the carb, covering
the throat.

With the engine idling, fuel dancing on the throttle plate. The bowl vent
tubes are right up at the top, probably on a 45 degree angle, and with
their ends cut off so they are flat to the horizon. If they are dribbling
fuel, this will be very obvious.

Is there a float bowl window on the side of this carb? That would settle
the float level thing without any disassembly.

 

Thanks to all who responded. I've decided to replace this relic. Know anyone
who might want it?

Richard D.