99 SL1 Saturn Runs Rough

My wifes car is a 1999 Saturn SL1 with about 85k miles on it. Up until this
last weekend it was running fine. I changed the oil on it and drove it a
bit and it ran fine. The next day my wife reported some major problems with
it. At idle it runs somewhat poorly. It seems to be missing every few
seconds. When the car is put in gear, that's when it really starts to
stumble and miss. The car really stumbles and hesitates when accelerating
up to about 25 mph. If you floor it, at high RPMs, the power seems to be
restored and it runs better, although not like what I am expecting. Of
course the check engine light is one. And when accelerating from a stop,
the check engine light may flash briefly.
At any rate, I don't have a Autozone close to me so I can't check the
engine codes. I have a date with the mechanic in a couple of days but would
love to solve the problem before then.
I change the oil again. Change the plugs. Changed the PCV valve.
Checked the resistance on the plug wires. Checked the air filter, and I
checked for any obvious wiring problems and vaccum leaks. I did not see any
obvious problems. I have not check the compression or anything in the gas
line. Any ideas?

 

I have a similar problem with my 2000 SW2 (manual shift). I brought
it to a shop for a routine tune-up, and when I got it back it had
problems. Tune up included new plug wires, re-gap existing plugs (I
asked them not to change them since I put new ones in recently),
change of air filter, oil & filter change, checking existing fuel
filter & keeping it because it "looked fine".

The overall symptoms are loss of mileage (~25 mpg down from ~35),
hesitation when accelerating, especially when first entering a higher
gear, and occasional stalling when slowing to a stop and putting it in
neurtral. One very strange thing is that the hesitation/stalling
problems only occur when the engine is WARM. It's perfectly normal
first thing in the morning.

I've read elsewhere that the engine temp sensor could be bad, but I
have my doubts in this case. The temp guage goes to its normal spot,
heat works as usual, etc. It seems as if something else isn't working
right once it gets the temperature data.

I took it back to the shop that did the tune-up, but they couldn't
find what was causing the problems.

There were no codes when I went to Autozone, but later I did get a
code lasting for a few minutes regarding the Throttle Position Sensor
(TPS). So I got some spray cleaner (the stuff made specifically for
fuel injected cars) and cleaned a lot of gunk out of the throttle
body, but the problem still exists.

Maybe it's the TPS itself, but it seems like an unlikely coincidence
that the TPS would happen to go at the same time that a simple oil
change or routine tune-up was done. It seems more likely that some
gunk was dislodged in the system somewhere as work was being done, and
the gunk made its way downstream, landed on a sensor, and is now
fouling things up. Sort of like a blood clot causing a stroke.

I'd like to check & clean more of the sensors, but my Haynes book has
not been overly helpful for this problem (although it's been great for
other things I've done).

Any idea how to get diagrams for the car's computer system --
component locations, wiring diagrams, etc? Helm's was recommended
(www.helminc.com), but I'd like some feedback from other Helm
customers that have used the book for troubleshooting the computer
system & sensors.

Thanks.

 

A good shop manual that gives information on the OBDII codes and of course a
code reader are very helpful to have. Helm publishes the shop manuals - same
ones that the dealer uses except that the dealers have the on-line versions.

TPS sensors can get noisy. It's basically the same idea as the gas gauge
sensor or the volume control on your old-school table radio. Moving the
sensor shaft moves a wiper against a resistance element. Over time the
contact between the moving parts wears and becomes erratic. This gives
electrical noise which the computer doesn't quite know how to make sense of.
Sometimes you can put voltmeter on the TPS and slowly move it over the full
range. Attach the meter from chassis ground to the output terminal on the
sensor (terminals are ground, 5V and output). voltage should be proportional
to sensor position and stable for any position. Not an expensive part, they
are usually more simple to just replace.
Drive by wire systems have dual sensor elements on both the throttle pedal
and throttle actuator for redundancy.
Oppie

I have a similar problem with my 2000 SW2 (manual shift). I brought
it to a shop for a routine tune-up, and when I got it back it had
problems. Tune up included new plug wires, re-gap existing plugs (I
asked them not to change them since I put new ones in recently),
change of air filter, oil & filter change, checking existing fuel
filter & keeping it because it "looked fine".

The overall symptoms are loss of mileage (~25 mpg down from ~35),
hesitation when accelerating, especially when first entering a higher
gear, and occasional stalling when slowing to a stop and putting it in
neurtral. One very strange thing is that the hesitation/stalling
problems only occur when the engine is WARM. It's perfectly normal
first thing in the morning.

I've read elsewhere that the engine temp sensor could be bad, but I
have my doubts in this case. The temp guage goes to its normal spot,
heat works as usual, etc. It seems as if something else isn't working
right once it gets the temperature data.

I took it back to the shop that did the tune-up, but they couldn't
find what was causing the problems.

There were no codes when I went to Autozone, but later I did get a
code lasting for a few minutes regarding the Throttle Position Sensor
(TPS). So I got some spray cleaner (the stuff made specifically for
fuel injected cars) and cleaned a lot of gunk out of the throttle
body, but the problem still exists.

Maybe it's the TPS itself, but it seems like an unlikely coincidence
that the TPS would happen to go at the same time that a simple oil
change or routine tune-up was done. It seems more likely that some
gunk was dislodged in the system somewhere as work was being done, and
the gunk made its way downstream, landed on a sensor, and is now
fouling things up. Sort of like a blood clot causing a stroke.

I'd like to check & clean more of the sensors, but my Haynes book has
not been overly helpful for this problem (although it's been great for
other things I've done).

Any idea how to get diagrams for the car's computer system --
component locations, wiring diagrams, etc? Helm's was recommended
(www.helminc.com), but I'd like some feedback from other Helm
customers that have used the book for troubleshooting the computer
system & sensors.

Thanks.

 

Well I will be at the shop tomorrow, so hopefully it will not be a big
problem. My problem occurrs when the car is hot or cold. I wonder if I
damaged a sensor, wire, or hose when I was doing the work. At any rate I
will find out soon.

 

chance are it is the tps, runs good at high rpm sucks at low rpm! If
it was a vacuum line it would idle high as verses come down to low
idle. The ts will be very erractic at low speed and almost kill the
engine. One other dangerous area is the plug gap. I had excellent gas
milage until I changed the plugs on my vehicle, gapped them at 40 per
spec so what was wrong? Well the milage turned out to b the point
gap.. mine are now gapped at 49-50 which increased my milage and
ALWAYS use standard copper type plugs. The 1.95 type of autolite or
ngk to work the best. Platiums always fail in a saturn!

 

Well I took the car in to the shop. Turns out we had a couple of clogged
fuel injectors. The diagnostic codes indicated that the car was misfiring,
and that it had a lean condition. Which makes sense if the engine is not
getting enough fuel from the injectors. At any rate, they were able to run
some injection cleaner through the system and now it is running much better.
Better than it has run in a long while.

Thanks to all that looked and responded.

chance are it is the tps, runs good at high rpm sucks at low rpm! If
it was a vacuum line it would idle high as verses come down to low
idle. The ts will be very erractic at low speed and almost kill the
engine. One other dangerous area is the plug gap. I had excellent gas
milage until I changed the plugs on my vehicle, gapped them at 40 per
spec so what was wrong? Well the milage turned out to b the point
gap.. mine are now gapped at 49-50 which increased my milage and
ALWAYS use standard copper type plugs. The 1.95 type of autolite or
ngk to work the best. Platiums always fail in a saturn!