I've had three Saturns: a 1995 SL1, 1998 SW and now a 1999 SL with a manual transmission. My plan was to keep the SL1 for the rest of my life, but it get rear ended by a 18-wheeler and walked away without a scratch. I'm 80 and want to keep this SL until I die. So, I'm walking through each problems one at a time.

Prior to achieving normal operating temperature (first mark on gauge), RPM tends to run at 2k. When running in gear at 1.5K. I can disengage the clutch and the RPM will jump to 2k or more (up to 3k)

Once at temperature, when I come to a stop RPM will linger at 1700 RPM for around twenty seconds before dropping down to 800k.

After running for awhile, RPM seems to act normally. I say "seems" because I normally don't drive more than two or three miles at a time and, as I remember, these symptoms are to a degree inconsistent. I read to replace the temperature sensor. Are there other areas I should be looking at?

 

Try a throttle body cleaning.

How many miles on it?

Operating temperature is usually about 3/8 on the temperature gauge. Halfway between the first and second tick. Your vehicle may not actually be getting up to operating temperature, as the normal idle speed when fully warmed up should be about $800 to 850 RPM.

If you are only driving 2 to 3 mi at a time, it is highly unlikely that the engine is truly getting up to operating temperature, at which point the idle should settle down.

Is the check engine light on? If so, take it to AutoZone or similar and ask them to read the codes. They will give you a printout with information of the form PXXXX. Post those diagnostic codes here. Do not, I repeat do not purchase anything from the parts store that reads your codes right after they are read.

One of the other possibilities is the throttle position sensor on the throttle body. Lack of heat and cleaning from the warming up May have it gunked up and therefore not smoothly telling the car's computer how far open the throttle plate is.

You may wish to have someone younger, for the sake of safety, take the vehicle out and drive it around for several hours once every two weeks through everything from city traffic to the highway and really get the engine warmed up. This keeps the deposits from hardening up as badly and also keeps some of the gaskets and seals from drying out and leaking.

I would let it idle for half an hour in your driveway before someone else takes it out to ensure that the cooling fans work when the engine gets hot enough and that there are no fluid leaks. By doing this, you can also tell whether the engine finally finds its way to a normal idle speed.

But first I would try the cleaning of the throttle body being sure to clean the idle air control IAC.

Don't go throwing parts at it. It's too expensive and makes it harder to figure out what is actually wrong.

 

The mileage is 150k and the check engine light has never come on. As far as my age, most people think I'm in my sixties although I do run like an old man. I drove a moving truck when I was young and I'm, still, a defensive driver. What you had to say about taking a several hours drive makes sense; will try to figure where to go.

Would like to be able to read the engine codes myself. Do you have any recommendations on a "cheap" code reader?

 

On amazon this is the code reader I purchased and used:

" MOTOPOWER MP69033 Car OBD2"

is what i use for my 1997 Saturn Sl1 it helped diagnose a failing O2 sensor. costs a whole $20 dollars.

Hope this helps!

I put this as a response on another post as well today (hope this doesn't count as double posting)

 

This was a simple fix (YouTube - How To Clean a Throttle Body on a Saturn S Series (SL, SL1, SL2)), but I don't have a garage and had to wait for a dry, warm day. The thing was filthy. Bought some official throat body spray for $6. The tools were a 10mm socket, short extension and a flat blade screwdriver used to release sensor clips and hose clamp. RPM is consistent and now drops to 800 although it lingers at 15k for 10 seconds or so before it drops.

The temperature is still at the 1/4 mark on the gauge. I checked the upper and lower hoses on the radiator and the upper hose is much hotter the lower one. I need to flush the cooling system and that seems like a good time to replace the thermostat.

Something I didn't mention in my original post was engine dieseling. I didn't think that high RPM due to a dirty throat body was connected to the dieseling, but it sure looks like it was; no more dieseling.

 

Glad to hear it, sir

 

Before replacing my thermostat i had the same issue. my thermostat was wide open so it' never go above just below the quarter marker. So I bought a GATES thermostat with the housing included. now my temps are fluctuating between just over the quarter mark and just below the halfway marker. It's a lot more consistent and my heater works a lot better. So I hope replacing the thermostat helps out your coolant temps!

 

Do not purchase the AC Delco Professional offering. It is made by Motorad. POS

 

Was planing to get a Murray Plus thermostat from O'Reilly. They have two that seem to be the same except for price. The name difference is that one has "185 Degree" in the title and the other is "192 Degree". I'm guessing that one is for warmer weather and the other for colder, and the 192 is double the price of the 185. Planing on getting the more expensive one.

 

I THINK 192 was the OEM temp for the thermostats, but am not positive as I'm NOT a mechanic.