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

[Richard (3)]

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.

 

[CaptainKrunch]

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

 

[TeGGeR®]

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.

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?

 

[Andrew Smit]

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

 

[Richard (3)]

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.

 

[Richard (3)]

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

 

[Richard (3)]

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.

 

[TeGGeR®]

Thanks, Tegger.

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

"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.

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

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.

 

[Richard (3)]

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

Richard D.