97 saturn sc2 bucking and won't rev up

my wife's car is a 1997 Saturn sc2 with 135,000 miles 2 days ago she left it
on the side of the road and said it would not run. I went with her to tow it
home and it started, drove for about 1/4 mile and died like someone turned
off the ignition. then it was starting and stalling and would not rev up. I
started towing her home and half way back she said it was running fine so I
disconnected her and she drove it the rest of the way home (about 3 miles).
2 years ago an auto mechanic changed one of the 2 ignition coils and my wife
said the car was doing the same thing. so I changed both ignition coils,
installed new plugs gapped to .0040, check the spark plug wires for to make
sure there was not one with very high resistance, and disconnected the
battery for 10 mins to reset the computer.
after all that, the car sometimes acts like it has a rev limiter at 4200
rpms and sometimes revs normal. and sometimes when it is warmed up it acts
like it is cold and idles up to about 1600 rpms like it is going into the
choke.
anyone have any idea's what could be wrong with the car? or what I should
check next? thanks carmine

 

You may want to stop by your local Saturn and get the codes read (and a
proper diagnosis) before spending any more money on parts. The car's PCM
usually knows what is wrong - you just need to ask it. It beats guessing
and the fee usually ends up paying for itself.

Lane [ l a n e @ p a i r . c o m ]

 

after all that, the car sometimes acts like it has a rev limiter at 4200

That definitly sounds like a coolant temp sensor. If its warmed up but idles
like its cold(in 'warm up' mode) that means the coolant temp sensor is telling
the computer the engine is cold.

There should be a rev limiter at around 4000 when the car is stopped, that is
normal.

 

I would suspect the alternator.

When the alternator goes, it does a couple of things:

1) It screws up the voltage that the transmission computer sees. This will
cause serious drivability problems.
2) The engine computer sees that the voltage is low, and idles the car
really high.

Check the alternator. If it's the alternator, I'd replace the alternator and
the battery. This is because sometimes a faulty alternator will kill a
battery, and a faulty battery will kill an alternator.

Also, if you haven't replaced the coolant temperature sensor yet, that would
be a good idea. The original one is plastic and VERY failure prone. A bad
engine temperature reading confuses the computer something awful. The sensor
itself is about $15.

You might also want to replace the connector to the temperature sensor,
because when the sensors go, they leak and corrode the sensor.

Good luck.

 

I would suspect the alternator.

If it started up again after it died, I would tend to doubt the alternator is
the culprit. It definitly sounds like some symptoms are that of a coolant temp
sensor. That should be the first step.

 

Only temporarily. If it's acting up it will set them again.

 

by reseting the computer did i wipe out the codes in the computer? thanks
carmine

 

the temp gauge is working in the car does the temp gauge work off of the
temp sensor? thanks carmine

 

It depends.

A shorted diode can cause lots of electrical noise to be injected into the
car's electrical system, confusing the computer(s). It can do this while
providing enough current (time averaged) to keep the battery charged up
enough.

But, it sure could be (as I noted in my original post) the coolant
temperature sensor also.

 

how can I check for a shorted diode. and how can I check the alternator.
today I put a new temperature sensor in the car and it still revs high
sometimes when it is warm. was I suppose to reset the computer after
installing the temperature sensor? thanks carmine

 

No, for some reason there are separate temp sensors for
the gauge and the engine computer, so when the sensor for the computer
is acting up and the car thinks the temp is too hot or too cold,
you have NO FRIGGIN IDEA what it thinks.

Never go to sea with two chronometers. Take one or three.

-DanD

 

From what I can tell, a 97 has only one sensor..

 

Man, that sounds like a fuel filter.
Joe