Idling Issues and others too!

[TheStu]

'98 Saturn SL2, 199,500 miles, 5 speed manual.
Starter replaced early '07
Clutch replaced mid '07
Water Pump replaced '08
Shift Linkage replaced '09

I have noticed my MPG start to decline over the past few months, from the low 30s to the upper 20s (33-34 down to ~27) and although not a huge deal, on my 10 gallon tank, that means I am filling up every 5 days or so instead of every 6 or 7. It is the winter, so the heater has been on pretty much all the time, but does that affect fuel economy that drastically? I have heard that it does, but the person I heard it from knows even less about cars than I do (and I know a little but not a lot, I know what I don't know, he doesn't even know to not keep using 3 year old wiper blades).

Anyway, in addition to that, it just recently started stalling sometimes, not every time, when I am idling at a stop. It turned off twice when I was trying to park, and a couple of other times but every other time it has just dipped real low on RPMs (needle touching 0) but didn't actually quit on me. Also, i saw a guy on here that had his idle RPMs at 2000, that happened just today to me as I was getting into work. I have to go through checkpoints, stopping 3-4 times before I actually park, and it was at 2000RPM each time. Never done that before, didn't do it after work.

So, what are the odds that this is a nice simple fix that I can do? I replaced the water pump, master/slave cylinders, and a couple of other things myself. And did some engine work on an OLD Chevy ('49), pulling and cleaning the fuel pump, replacing the jets in the carburetor, gaskets on the manifolds, that sort of thing.

If it was a simple thing that would be great, I have a 700+ mile drive coming up in a couple of weeks, and want my car back in shape for long distance.

 

[Aikouka]

I recall on one of my older cars when I was having idling issues, there was something I had to tune to get the idle in the "right spot." Unfortunately, I can't recall exactly what it was. But I'm not so sure that's even what would cause such a random idle (low and high rather than just one or the other).

Mileage declining in the winter months isn't too odd at all.

 

[Howard]

Heater doesn't change mileage much. The gas itself does, among other things.

 

[LTC8K6]

Isn't there a common temp sensor problem on those? ECT?

 

[5150MyU]

You need to start with the basics at 2k-clean TB and IAC.
TB=throttle body
IAC=intake(idle)air control
Unfortunatly you need a scan tool to check these.
IAT=intake air temperture sensor-if the car has it-this can reak havoc with the computer-this will not generally set a code but you will see your MPG drop to 2 LOL.
ECT=engine coolant temperture sensor-not good either-same as IAT.
And that's just to start.

 

[Vetterin]

I know this doesn't answer your question but just FYI I think your gas tank is 12.1 gallons.
Are you familar with Saturanfans.com? Great site for Saturn owners.

 

[TheStu]

You need to start with the basics at 2k-clean TB and IAC.
TB=throttle body
IAC=intake(idle)air control
Unfortunatly you need a scan tool to check these.
IAT=intake air temperture sensor-if the car has it-this can reak havoc with the computer-this will not generally set a code but you will see your MPG drop to 2 LOL.
ECT=engine coolant temperture sensor-not good either-same as IAT.
And that's just to start.

How much does it usually cost for a scan? And when you say that I will see my MPG drop to 2, do you mean that the car will actually only got 2 miles/gallon or that the computer will read it out that way?

I know this doesn't answer your question but just FYI I think your gas tank is 12.1 gallons.
Are you familar with Saturanfans.com? Great site for Saturn owners.

Well, just going off of personal experience, the one time that my fuel tank was really freakishly low, with the light blinking at me and all that, I put 11 gallons into it. Every other time I fuel up close to E it is 10 gal or less.

 

[5150MyU]

I was being sarcastic with the 2 mpg-but if the cam sensor is not reading correctly it wouldn't surprise me if you lost 2-4 miles per gallon.
As for the scan-dealership is gonna charge you 1 hour, friendly neighborhood mechanic with a SNAP-ON brick may do it for free.
You need to verify that the sensors are accurate.
That means not just reading in their range but actual temperture.
EX.IAT=-35 when it is 70 out side
ECT=100 when the engine is fully warmed up and running at 195.
I can explain better if you don't get what I said.

 

[kornphlake]

Most likely it's the ECT already mentioned, I'm not sure of a good source for a replacement these days, but the part from a saturn dealership is the one that will fix the problem, aftermarket parts will not in this instance, cost is about $20 for the part IIRC. GM dealers are supposed to be able to get Saturn parts, I've never tried and I don't know what is involved.

You are probably due for a new thermostat, your temp gauge should read about 3/8 when the engine is warmed up. With a working thermostat you should only have to drive 2-3 minutes for the temp gauge to reach 3/8. The ECU is programmed to idle high (around 2k rpm) until the engine reaches a certain temp. High idle with a warm engine is caused by the sensor is giving an inaccurate reading and the ECU adjusting the idle for a cold engine. Thermostats typically fail open, if the thermostat is stuck open and you live somewhere the temps are pretty low your engine may not warm up enough to switch the ECU to normal idle once in a while. A bad thermostat could magnify a problem with an already marginal ECT sensor.

Does your gas pedal stick sometimes? Cleaning the throttle body will fix that and should help the car idle a little better, clean the IAT while your at it and the idle should smooth out considerably. The throttle position sensor isn't known to be a problem in Saturns but could be causing trouble, it's easy to test with a multimeter and it makes sense to do so while you're goofing with the throttle body.

Working on a saturn is really simple, the hardest part is finding the part physically in the engine bay, most of the problems are very common and fairly easy to diagnose over the internet. If you have a few basic hand tools you can probably make the repairs yourself.

 

[TheStu]

Most likely it's the ECT already mentioned, I'm not sure of a good source for a replacement these days, but the part from a saturn dealership is the one that will fix the problem, aftermarket parts will not in this instance, cost is about $20 for the part IIRC. GM dealers are supposed to be able to get Saturn parts, I've never tried and I don't know what is involved.

You are probably due for a new thermostat, your temp gauge should read about 3/8 when the engine is warmed up. With a working thermostat you should only have to drive 2-3 minutes for the temp gauge to reach 3/8. The ECU is programmed to idle high (around 2k rpm) until the engine reaches a certain temp. High idle with a warm engine is caused by the sensor is giving an inaccurate reading and the ECU adjusting the idle for a cold engine. Thermostats typically fail open, if the thermostat is stuck open and you live somewhere the temps are pretty low your engine may not warm up enough to switch the ECU to normal idle once in a while. A bad thermostat could magnify a problem with an already marginal ECT sensor.

Does your gas pedal stick sometimes? Cleaning the throttle body will fix that and should help the car idle a little better, clean the IAT while your at it and the idle should smooth out considerably. The throttle position sensor isn't known to be a problem in Saturns but could be causing trouble, it's easy to test with a multimeter and it makes sense to do so while you're goofing with the throttle body.

Working on a saturn is really simple, the hardest part is finding the part physically in the engine bay, most of the problems are very common and fairly easy to diagnose over the internet. If you have a few basic hand tools you can probably make the repairs yourself.

I think that the thermostat was replaced with the water pump, and yes it takes about 2-3 minutes of driving (sometimes a little more) for the temp gauge to get to the right point.

And I don't know if this is related, or even a real problem but when I get up to highway speed (70), I can hear the engine more than I remember. The RPMs seem to be in the right place, in fifth gear, above 50 or so the RPM and MPH needles are just about exactly at the same angle, but it just sounds like the engine is working harder or something.

 

[Vetterin]

Well, just going off of personal experience, the one time that my fuel tank was really freakishly low, with the light blinking at me and all that, I put 11 gallons into it. Every other time I fuel up close to E it is 10 gal or less.

Well, that sounds about right because when your low light comes on you should have about 40-50 miles of gas remaining in your tank (1-1/2 to 2 gals). FWIW, I bought my wife a new 02 SL2 and now 9 yrs and 140K miles later it still runs (and looks) fine.
Just a thought but have you changed your fuel filter?

 

[TheStu]

Well, that sounds about right because when your low light comes on you should have about 40-50 miles of gas remaining in your tank (1-1/2 to 2 gals). FWIW, I bought my wife a new 02 SL2 and now 9 yrs and 140K miles later it still runs (and looks) fine.
Just a thought but have you changed your fuel filter?

I am not sure when, if ever, the fuel filter was replaced.