ADHA - no fast idle

[pwilliam]

Hi all,

My 79 automatic has suddenly failed to engage the fast idle. The spring seems fine on the auto choke so I'm not sure why it is not engaging. Has anyone encountered this problem before?

If I start the car it will die as soon as I stop pumping the accelerator pedal. If I leave my foot on the accelerator pedal for about two minutes the car will shift into drive without much issue. However, there is about a drop of 400 rpms when I do this which brings it down to about 500 rpm.

If I start the car, don't wait for it to warm and give it gas, quickly shifting into drive, I'll take off without issue but experience the same drop in rpm's mentioned above.

After driving for some time, the car will idle appropriately and if I give the car a warm start it will also idle appropriately.

Recently replaced rattling catalytic converter with california emissions approved converter from midwest-bayless. This problem arose about 300 miles later.

Any thoughts?

[pwilliam]

Not sure how I managed to post 3 times. Sorry.

[garion]

Does that carb have a idle cutoff solenoid? If so, then check to make sure its hooked up and function. It should have 12V, and you should be able to hear it click as you connect/disconnect it with the ignition on.

[So Cal Mark]

you're going to have to remove the choke cover and look at the lever inside the housing to see if it's gummed up or broken

[pwilliam]

Solenoid is clicking. I'll take a look inside this weekend. Thanks for the advice.

[manoa matt]

Sounds like a problem I encountered with a friends 79 auto a few years back. Same symptoms. There is a small white plastic cam on the bottom side of the choke housing. The plastic is old and brittle, when that piece snaps off, you can't tune the carb. I ended up replacing the stock 28/32ADHA with a 32ADFA from an 1800. Ran much better with more zip.

[pwilliam]

I didn't notice a plastic cam when taking the choke cover off. Does anyone have a photo for reference? (Who am I kidding most people have probably ditched their ADHA at first chance!) Everything looked normal inside. There was a lot of carbon build up on the thermostatic coil of metal that controls the idle lever. I turned the screw out six full rotations to try to open the throttle more but it had no effect, so I turned it back in. After I put the it all back together the car seems to idle a little better, stalling out only once or twice now, opposed to the five or six times before.

I did notice that the screw would occasionally slide past the stepped idle cam when I pressed against it - but there is no way for me to tell if this is happening on start up. Pushing on the throttle would pull the screw out and reset the lever, so if that were the case, giving the car gas should fix that issue. There also wasnt any wear or streaks on the side of the idle cam to suggest the screw was continually sliding past it.


Tell me if anyone thinks this might be the problem...Three of the bolts that hold the air cleaner gasket on the carb stripped out so I removed them during the winter. One bolt remained and I believe (not 100% sure) I left the washer and the bolt on it. I had removed the metal retainer plate that is used to help press the gasket onto the carb. When my dad took the cover off of the cleaner he noticed a washer sitting right next to the carb but there was no nut on the bolt.

If the bolt worked its way off and fell into the carb, then worked its way into a cylinder and caused some damage...is it possible that I would have a poor fast idle (to the point of stalling out) due to only three cylinders firing? I'll try pulling the plugs this week to see if I can notice any damage.

[majicwrench]

You would know if something got into cylinder. If you have to pump throttle to keep it running, it is too lean, not a fast idle can type issue. Does it idle well warm? But hand over carb to slightly restict air flow, does idle improve?? What rpm is hot idle??
It is clearly stepping up onto fast idle cam. Looks like that part is working.
Fix stripped stuff. Tacky.
Keith

[pwilliam]

Car idle's well when warm. If I have been driving and the engine warms up, the idle is at 900 rpm. I'll try adjusting the mixture and see if that improves or if hand over the carb helps.

My concern is that this issue suddenly appeared after the car running fine for months. I had made no adjustments to the carb to alter the mixture. Any thoughts on what could make the carb go out of synch and cause this problem?

[majicwrench]

Obviously any number of things can change in an instant. That is why ilde mix/soleniod has been mentioned several times, it is an easy to plug system. Usually when idle/slow jet plugs, car runs terrible cold, hesitates, once warm kinda acceptable or no idle.
Your idle is a tad high, but not too much so. Cup hand over carb w engine idling and see if it improves idle quality.
Keith

[pwilliam]

Cupping my hand over the carb helped to improve the idle. I'll adjust the mixture tonight and see how she does. Thanks for the help, Keith.

[pwilliam]

Car idled better after mixture adjustment, but still too low, consistently around 1100 rpm on cold start and wouldnt go past without adjusting the idle speed screw. I turned the screw back down to where it was before I started and the car was really hesitating upon acceleration. It even stalled out at a stop sign, heading uphill. I'm going to reset it to factory specs per the Artigue guide tomorrow. If the issue persists does anyone have any suggestions on what to troubleshoot next?

[seabeelt]

Is the choke all the way closed at cold start ( no gap between the choke flap and the Venturi side wall)?

[pwilliam]

No, I don't think it is.

[seabeelt]

That will need to be all the way closed as a starting point. Adjust that first.