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95 Buick Century Woody Rough Idle - Battery?

My grandpa’s old wood paneled station wagon is sick. The idle seems to be getting rougher and rougher with every time I kill the battery (I’ve somehow left my headlights on four times in the past two months and needed a jump). It’s to a point now where if I don’t throw it in neutral at stop lights and keep a tiny bit of gas on the engine it stalls out.

*When it first gets jumped after being dead, if I stop even for a second, it dies instantly.
*While cruising - it is fine.
*It idles smoother stopped in neutral than it does stopped and in drive.
*It seems a bit rougher with the engine is cold, but still rough and can stall with the engine hot.
*Some random times it idles just fine (like for example the first few seconds on start up, and then it sounds like the engine is decreasing in rpm automatically, and then it is rough again).

Could the dying battery and rough idle be related?? The battery guy says “if it starts fine, the battery is fine” (it does start fine, although keeping the radio on for 20 minutes without it running will kill it).

Also other problems with my car in case this has anything to do with it:
*I have a leaky tail pipe
*my ABS has recently been randomly engaging at low speeds (next problem to work on…)

Ideas??? Thanks!

a battery . . and running/idling . . are not related.
Has this car been parked a great deal ?
It could have an old weak battery . . have it ‘‘load’’ tested.
But if it’s been parked or rarely driven ( as is my 1979 Chevy pickup ) it could be suffering from. .
old gas !
When you first mentioned old car . . my first thought was old gas.
Smell it.
If it doesn’t smell like the new gas you get at the gas station today. . renew it.

In a car that age, rubber and plastic parts start to age out regardless of miles.
you could have vacuum leaks, fuel pump problems, throttle body issues and other dry out caused problems.

I had similar running problems with my 79 . I’d drive it once or twice a year but could easily stretch two years between fill ups.
– old gas – reared its ugly head.
Most people don’t think of their cars in the same breath as when those same people add Staybil to the fuel for their boat, chain saw, atv, generator, and other obvious rarely used fuel supplies.
Now I keep Staybil in the tanks of the 79 and it starts right up.

The problem you describe sounds like the Idle Air Control valve isn’t functioning right.

Sometimes removing the IAC valve from the throttle body and cleaning it along with the throttle body with throttle body cleaner will get it to functioning again. Other times the IAC valve requires replacing.


If you can put a battery charger on the battery - do it. Once you know the battery is fully charged, then see how it idles.

The battery guy says "if it starts fine, the battery is fine"
You might want look for a new battery guy, that is a bad assumption.

keeping the radio on for 20 minutes without it running will kill it
That’s what we call a bad battery (assuming factory level stereo draw)

First I would look at lots of mechanical reasons to have a rough/poor Idle. But I’m going to assume you have done that or REALLY are certain on the dead battery cause.

A weak Battery, will show off problems with the charging/generation system. Check you Alternator, and its wiring. When your car is running, its not using the battery at all (other than charging it). The Battery (when good) is ~12V. Your alternator puts out 13.5 -14v all the time. (that’s how your batter charges, Higher voltage makes current flow backwards into the battery)

Lots of Sensors in your engine are voltage dependent (to an extent) if your Car’s voltage gets to 8v it will stall. But this will require both the battery and the Alternator to fail.

Another possible issue is that your bad battery is ‘’‘Charging’’’, drawing so much current to try and recover that your alternator can’t keep up. An alternator is a generator, that can only make so much power based on engine speed (Power = Volts x Amps[current]). Your stall condition is idle, when your engine is turning its slowest, which means your alternator produces the least amount of current. So a big useless draw from a battery might be your problem.

Otherwise your alternator is really a 3phase AC generator, (three power outputs) that is then sent to a Rectifier to be converted to DC (in a 95’ Buick its internal in the alternator). An AC Generator works by spinning magnet inside of some wire coils. To make it’s voltage output be 14v regardless of engine speed, the spinning magnet is replaced with an spinning electric magnet, which is fed from a “Field Coil” wire in wire harness. This varying strength magnet, auto adjusts to keep outputting 14v, no mater how much current you use, or how fast your engine is turning (within the alternator physical limits)

If one of the three power outputs in the AC generator dies, or if one the Rectifier parts related to one of those power wires (a common fault), your power is bad Your Alternator output is then not true DC and will be significantly impaired. The auto adjusting nature will bring the output of the reaming two up, to try and compensate, but its a losing battle.

The big output Wire on your alternator and the “Field Coil” wire are electrically the same (95 buick I think there both in the same connector). They are separate wires because of something called Voltage drop, which occurs on the high current output wire. If your “Field Coil” wire is damaged, or the connector is dirty (really anything that ups the resistance) This will impact the alternators view of its output. Which could lower your operating voltage.

Hope that helps

Awesome!! Y’all are the best!

Update: I just took it on an hour drive, and the last few minutes when pulling into my driveway the power steering went out, the battery light came on, but the car kept running (poorly, and the breaks didn’t give out like it does when the whole thing dies)… only the steering went out!!

I’m not driving this thing again until I fix it…

Look for a broken fan / drive belt

That’s it! The alternator froze up and broke my belt. Thanks so much! Any idea why an alternator freezes up? Just old or something else wrong? Also - do I need a new alternator, rebuild, or maybe there is something I can spray on it orrrr something (the car is a POS, cheaper fix the better…)? It was stuck and I put some force on it and now it (not smoothly) turns.

Frozen alternator = replacement

Things do wear out.