1989 Chrysler Fifth Avenue still idling rough/stalling after carburetor work?

Hello! I don’t know my way around under a hood, so apologies in advance for my layperson’s terms.

About eight months ago, I purchased a 1989 Chrysler Fifth Avenue in very good shape with no major mechanical issues. Over the past couple months, she starts idling rough and having trouble starting and accelerating with increased frequency. Eventually she just starts shuddering and stalling whenever idling, whether in gear or not.

The battery was brand new so I rule that out. I get her new spark plugs, but my mechanic suspects the carburetor was the culprit, which he can’t help me with.

So I bring her to a second mechanic. He cleans the carburetor and replaces the old gasket, resistor, and preheater hose, which were all but disintegrated.

I pick her up and do a test drive; no change, still sputtering to a stall at every red light. I bring her back and report; mechanic says he needs to “adjust the idle.”

I pick her up again, and she’s… only marginally better. It’s been a few days now, and while she hasn’t stalled (well, once now), she really wants to. Every stop in traffic, she shimmies and shudders and desperately wants to go back to sleep, until I hit the gas again.

Just a few months ago, she was (usually) purring like a kitten. I’m hesitant to bring her back to this guy for a third time; I don’t think he was trying to fleece me or anything, but I can’t shake the feeling that he’s barking up the wrong tree.

Any thoughts or advice would be greatly appreciated.

Are you sure you have a carburetor? IIRC Chrysler was using throttle body fuel injection in 1989.

It’s the worst of both worlds, the electronic feedback carb.


I think I’ve blocked those from my memory.


Yes it has a carburetor! In 1989! It is a 2 barrel electronic carb.

A car this old running on modern gasoline with ethanol in it may need more that a carb cleaning. It may need a rebuilt unit. The car may also need a new fuel filter, fuel pump and maybe even carefully inspect the rubber fuel lines for deterioration.

Very old cars don’t like ethanol laden fuel.


I’ve rebuilt a bunch of carbs using ethanol resistant components, fortunately never an electronic feedback one.


Yeah, on the advice of the second mechanic I’ve started using an ethanol stabilizer… probably about 20+ years too late.

Anyway, thank you kindly for the tips.

Has the ignition system been checked? Cap/rotor/wires/plugs? Fairly common for ‘carb’ issues to actually be ignition issues.

Rockauto does have a rebuilt carb, if it comes to that.

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The old lean burn system and carb…

Might want to make sure he is adjusting the idle mixture screw(s) correctly and also making sure the base timing is correct…

You are going to need to find an old school mechanic that knows these cars…

I would do a Lean Burn "conversion " to the earlier electronic ignition, or better stated as Lean Burn system removal kit… Summit, Jegs and others sell the kits…

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Change the plug wires first. Everything else comes afterward. Get the expensive ones.
Make sure the EGR valve isn’t stuck open. Check for frayed wires in the distributor if you have vacuum advance.


No experience with your car, but I recently had similar problem with older Ford carbureted truck. Poor idle, misfiring at idle when engine warm, but idled ok cold, and ran well at higher rpms, no misfires when rapidly accelerating or going fast. Long story short, after some experiments with ignition system that had no effect, I removed the carb and cleaned its idle pathways. Reinstalled carb, problem solved. Noticed some grit at bottom of carb fuel bowl, so replaced fuel filter as part of job.

As mentioned above, your carb is considerably more complicated than my truck’s. They were doing everything possible to meet fed clean air standards using a carb, yet not be forced to switch to fuel injection.

Were I in your situation though I’d replace everything that is clearly near the end of its life, clean the carb’s idle pathways, replace the air and fuel filters, eliminate all vacuum system leaks, and go from there.

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The first thing to do is make sure the choke is working right.

And you can do this yourself.

With the engine cold, remove the air cleaner cover.so the choke can be observed.

Step on the gas pedal once.

The choke plate should close.

Start the engine.

The choke plate should open just slightly.

Step on the gas pedal.

The choke plate should slightly open with each time the gas pedal is stepped on, and close when released.

All the while you’re doing this, you should notice the choke plate is opening more and more on its own as the engine idles.

When the engine gets warm enough, the choke plate should be wide open.

If you don’t see any of this occurring, there’s a problem in the choke system.



Just out of curiosity. since no one asked. and your mechanics do not seem to be the best. Is there or has the check engine light come on?
If it has there can be a code stored that might give a clue to the problem.

Just my opinion: “ethanol stabilizers” are essentially worthless.
All fuel delivery components need to be replaced with ethanol compatible materials.

I think Dave is on the right track with the above kits.

Your main problem is finding a mechanic old enough that has worked on these cars.


Here’s a great video describing how Chrysler’s Lean Burn system worked.

The Chrysler Lean Burn engine control system: first onboard auto computer | Allpar Forums

In theory, it was admirable. In practice, however, the implementation had its shortcomings.


Solving problems with those complex feedback computer controlled carbs has always been difficult. My parents had a Subaru so-equipped, and finally had to sell the car to the mechanic b/c it was costing too much to keep it running due to complicated carb diagnosis. I’ve never had to face that problem myself, but if I did I’d try to disable all the functions except for the fuel delivery in proportion to airflow. No o2 sensor feedback, no temperature adjustments, etc. If car wouldn’t start b/c choke disabled, a dose of starter spray into the intake manifold should solve that. Not sure however if the “back to basics” method is practical b/c the computer software may block each and every attempt to eliminate unnecessary functions.

If it has an AAP (Aux. Accelerator Pump) the AAP diaphragm may be leaking. That’ll make it run way too rich. I wore out a couple or more on my 1979 Toyota truck. Eventually I disabled the AAP system by plugging one of its vacuum hoses with a ball bearing or piece of a nail. The engine ran better that way.

lol… well there’s always that method … if in Calif, might not be such a good idea, big fine possible when fiddling with emissions systems components.

One test I always do when diagnosing my truck’s carb is to fill the fuel bowl with gasoline, and place the carb over a container, let it sit overnight. Nothing should leak from the carb into the container. If it does, that leak must be repaired. All gasoline safety precautions apply of course.

There’s a good case to be made that the AAP is not an emission system component. Its job is to enrichen the mixture when accelerating. By disabling it, there’s less gas being drawn into the carb, therefore less HC in the exhaust.

Blocking its vac hose with a BB or piece of nail of the correct diameter is unlikely to attract anyone’s attention, so the case may never have to be made.


And if not in Calif or has to go through emissions testing then get ride of the lean burn, block off the EGR (not worth a crap on old Mopar’s anyway) and install a 76ish 2 barrel 318 carb on it… Life will be WAY simpler… If you want to add some performance we can talk about that also…

If you have to go through emissions testing and they don’t look under the hood do the above and when time to test, retard the timing, and lean out the carb and pass away… These engines are very dependable…