Rochester carburetor '76 *bizarre* update

[Jeff Moffo]

Good afternoon
Wondering if someone has had this same experience. When I start my Coupe Deville on cold engine, the engine turns over, idles high until I kick it down. I often need to kick it down twice. Usually idle goes down and idles perfectly and one could barely hear the engine. However if I give it a little gas thereafter the idle goes back up and stays higher than it should be. It often happens even after the car has been taken out on the road and driven. Seems once I get it to a light or such, idle goes back higher. Car has 36,000 miles. I drive it maybe once every three weeks for 8 or so miles. Any ideas why this happens? 
Thanks
Jeff

[Jon S]

It could be the linkages are sticky and need to be sprayed with carburator cleaner at the connection joints.

[Jeff Moffo]

Choke side or accelerator pump side?  I'm guessing the choke linkages.

[Jon S]

Choke side but I would spray all linkages.

[Julien Abrahams]

Maybe a silly idea, but does the car get a chance to fully warm up? I don't know the climate your driving in, but if the engine is not warm enough, the choke will not open far enough for the idle to come down.
It happens to mine as well when I want to put it on low idle too soon (by tapping the throttle).

[Jeff Moffo]

It happens in all seasons. Doesn't matter if it is cold or warm outside.  Seems to happen only with engine cold. Seeing the car sits garaged most of the time, I will warm it considerably before I kick it down.  Then the idle is perfect.   If I start the car with a warmer engine, idle will be slightly higher than after the kick down idle - actually a little too high.  Even shifting in R or D causes the car to jump and begin moving too fast.

[Julien Abrahams]

Oh ok. Then it cannot be my suggestion. Could be what Jon said: try to clean the linkages. Is it an electric choke?
Could it be binding somewhere? I am not familiar with the electric chokes, but can they be adjusted?

[TJ Hopland]

Electric choke started in 75.   Could be cruddy connections not letting it heat properly.   It grounds through the carb body so there are lots of places to loose the connection.

Seems unlikely that you would have serious wear issues with that low of mileage but anything is possible.   When you get worn throttle shafts all the little catches and cams don't work right.

All that choke and high idle stuff is fairly flimsy parts that for the most part just work of gravity so it does not take much corrosion to keep them from doing their thing properly. 

IT would also be worth checking the vacuum brakes/pull offs.   I don't remember if a 76 just has one or if there are 2.  Sometimes those get involved with the choke operation.  If you have one that is leaking (which is likely at this age) or even a cracked vacuum line you could be just on the edge of it working properly then when you accelerate and the vacuum signal drops it also drops and this is what gets you back on high idle.

[Jon S]

Start with the linkages - make sure they are all free and gum-free. 

[EAM 17806]

Be certain the linkage pullback spring is properly attached and still has the tension it should along with the vacuum choke pull-off and its adjustment.  EAM

[Jeff Moffo]

I sprayed one side.  Will do the other next time I get in the garage and get it running.  Hopefully, that might be the culprit.
Other than those small issues, the car runs great.  It just gets frustrating when it is running so smoothly, I back it out of the driveway and 10 minutes into the ride or so, the idle becomes too high.  If I take my foot off the break at a light, she's on her way without much help!

[Caddyjack]

One possibility not mentioned yet is your oil pressure switch. If it's malfunctioning, then the electrical current to the choke spring-coil could be disrupted, causing the choke to not disengage.

[Jon S]

Good point, but it dis-engages and then re-engages.

[Alan Harris CLC#1513]

Could be that the throttle return spring has gone weak. I have had this happen on a couple of cars of different vintages. It produces the symptoms you describe. Easy enough to check out.

[Jeff Moffo]

Hmmm. Is that the spring on the drivers side of carb? 
Oil pressure switch is brand new as the old one was bad. It did it with the old switch, too by the way.

[Caddyjack]

No, the spring inside the choke housing that heats up with the electric current and opens the choke.  The thermostatic coil, if you will. Maybe the wire that connects there is loose or has a short somewhere.

[Jeff Moffo]

Was out spraying linkages etc this weekend. Car started. Choke opened slightly with pull off. Car began idling high. Kicked it down after about 1 min. Waited. Kicked it down again.  After the two kick downs and with the choke plate fully opened it idled perfectly. Got it out on the road and within 5 minutes of driving, idle was back up and not coming down. Not a super high idle like when started but higher than is considered normal. I'm wondering if its the curb idle that needs attention!?

[Julien Abrahams]

I presume that you have AC? I am not sure about '76, but in '67 the iele speeds up slightly (due to à slibt advancement in The timing. Could that be what is happenings to your idle?  I believe it is controlled by the climate control system. As soon as you turn it on ( besides full heat) it applies  extea vaccuum to the distributor.
Just a thought.

[mgbeda]

Here's a kind of out there idea, but...

Assuming the car is set up like original, there's a thermal controlled vacuum switch that sends vacuum to the EFE valve by the RH exhaust manifold.  What if there was a leak in that EFE valve?  The car would have a vacuum leak when it was cold, which could cause it to idle more slowly, but when it warmed up the thermal switch would shut off, the vacuum leak would stop and the car's idle would speed up.

-mB

[Jeff Moffo]

Hi Mike. Thanks for your response. Great posts about your own Cadillac restoration as well.
Car is totally original. So the set up would not have changed. What exactly does the EFE Valve do?
I'm included to believe it has more to do with the throttle linkage and/or throttle springs. Yet, I will keep the EFE Valve in mind.