Rough Idle/Dying - 97 SL2

[jessicaelaine]

We've been having issues off and on with our car having a rough idle, more off than on and usually fixed by turning the car off and starting it again. Last week, though, the car died while driving down the road. It was late, so we just pulled over, restarted the car, and I continued on my way. On my way home a couple hours later, the car was running fine until I had to stop for a train. As soon as I pressed on the gas after waiting for the train, the car sputtered and died. It struggled to start, until the battery was dead.

At this point I pushed it off the side of the road and a random nice guy (those are the best!) tried to jump my car. It wouldn't start right away, so we waited about 10 minutes and then started it, and he followed me the 6 or so blocks home. It still struggled when I'd accelerate from a stop, but I did get home. He suggested I leave it running, so the battery could charge a bit - but when I came outside half an hour later, the car was dead again, complete with the not starting and eventually a dead battery.

The battery was new about 2 1/2 or 3 years ago. I know that my serpentine belt needs changed, and I procrastinated changing it - but my new one will be in Thursday.

Is there any hope that changing the serpentine belt will fix whatever is going on? Or am I likely looking at replacing my alternator... which I'd rather not have to do both because of cost and because it's about 20 degrees for a high outside most days?

(We had the fuel pump replaced 2 1/2 years ago. The spark plugs and wires were changed last winter, and we've probably put 10,000 miles max on it since then.)

[bluesl2]

It sounds like there is a charging system problem. Is your serpentine belt tight, maybe there is a tensioner issue causing the belt to slip. If you can get the engine started, check across the battery posts with a voltmeter and see what voltage you have.

[jessicaelaine]

The belt is worn and loose, and needs replaced for sure.

Sort of a side-topic, but we've also not been getting a very considerable amount of "power" behind our heat, even when turned on high - especially not compared to even a few months ago. Could that also be the serpentine belt?

[fdryer]

A loose belt is usually due to a worn out belt tensioner. Unlike 'V' belts that always stretched (from bygone days), serpentine belts are made not to stretch at all. The spring loaded belt tensioner applies tension to keep a serp belt tight. Some tensioners break and fail to hold a belt tight so power steering, a/c, water pump and alternator never run correctly as the loose belt doesn't transfer engine power to these accessories. Pressing the serp belt should allow it to deflect at all with a good belt tensioner.

Losing heat may be due to two issues; the infamous original plastic tipped coolant sensor and a worn out thermostat. If your temperature gauge needle hovers over the 1/4 mark, the original coolant sensor and worn out t-stat may be the reason for lack of heat. Once both are replaced, the heater will be more than sufficient.

[jessicaelaine]

Originally Posted by fdryer

A loose belt is usually due to a worn out belt tensioner. Unlike 'V' belts that always stretched (from bygone days), serpentine belts are made not to stretch at all. The spring loaded belt tensioner applies tension to keep a serp belt tight. Some tensioners break and fail to hold a belt tight so power steering, a/c, water pump and alternator never run correctly as the loose belt doesn't transfer engine power to these accessories. Pressing the serp belt should allow it to deflect at all with a good belt tensioner.

Losing heat may be due to two issues; the infamous original plastic tipped coolant sensor and a worn out thermostat. If your temperature gauge needle hovers over the 1/4 mark, the original coolant sensor and worn out t-stat may be the reason for lack of heat. Once both are replaced, the heater will be more than sufficient.

I replaced the ECT sensor last December. It's not so much an issue of the temperature of the heat, as that it's just not blowing well at all.

I'll look into replacing the tensioner this week, as well. Do you recommend the entire tensioner assembly or just the pulley?

[fdryer]

The entire tensioner should be replaced. The pulley does nothing without the clock spring to pull the pulley against the belt. Before replacing anything, examine the drive belt system. There should be little to no slack and pressing down on the belt with your fingers should not allow the belt to deflect. If the belt deflects easily, the tensioner is worn out. Specs are between 40-60 lbs of spring tension applied to a serp belt.

If you live where leaves or tree litter clogs the hvac intake, you may have to remove the blower motor and stick your hand up into the fan housing to retrieve debris collecting and possibly block airflow. If airflow is good, the t-stat may be worn out. Some find a blocked outlet fitting, feeding coolant to the heater core. This usually requires disconnecting hoses and probing the fitting for blockage while manually flushing out the heater core in two directions to flush out anything clogging heater hoses/heater core. If you have to disconnect and and flush the heater core, fittings and hoses, use plain water until you're assured correct heat is coming out the vents. Do this all at one time to prevent water from freezing. Once assured the heater is working (replacing the t-stat if necessary), drain all water and refill with a gallon of 100% antifreeze and top off with plain water.