High Rev on idle

Hey guys,

I just bought a 97 Saturn SW1 as a secondary car to drive to work. When I bought the car it would usually rev up to 3000 everytime I would get out of a gear. It also had trouble starting from cold. But when it finally started it would idle at 2500-3000 for maybe 5 seconds before it dropped down to the normal 1200 (i forgot the exact number) rpm. Also, once I started driving it in the morning it would die on me a couple times when I pressed the accelerator. Then it drove just fine.

So here is the deal. The genius I am I thought that I could make it better, and of course it backfired on me.

I took out the throttle body and found a carbon deposit of about 1/4 inch on the back of the valve! I was excited that I found the reason for all those problems but after I cleaned it and put it back in, my rpm tried to shoot through the roof when I started the car. I checked all the connections to the sensors and everything seemed fine. So I tried it again and once again the rev just go up without any intentions to stop. I've also noticed a lot of smoke coming from the exhaust, which it didn't do before.

I started the car again and noticed that it is bouncing of 4500 rpm and hitting it like a limit bounding back to 4400 and then going back 4500. it completely freaks me out becuase it seems like that thing is about to blow up.

I was wondering why there is so much air going into it to let it rev that high, so i disconnected the cable to the throttle body to make sure the valve stay close but i didn't have the slightest effect.

What could be the reason for this?

Also, to my dismay, I see a few wires that seem to come from our regular Wal-Mart electroncs section, taped into the factory wire harness in several places under the hood.

Could it be the idle controller? Does it have one?

Any help is greatly appreciated!!!

There are many knowledgeable people here on the forum. I am not one of them but I have received very good advice.

I have a 2000 SL 5 speed manual 1.9L sohc with 163k miles. I also tried my hand at diagnosing and fixing my engine problems. I learned a lot but did not fix it myself.

One cause of a high idle that stays high is a leaking intake manifold gasket. My engine codes were high idle and #1 cylinder misfire. Turns out, those are classic examples of a leaking gasket near the #1 cylinder. That was my main problem.

However, prior to that, I replaced my idle air control valve. Since that wasn't the problem, it had no effect on my symptoms.

When the big moment arrived to start my engine with the new valve, it started and red lined. I shut it down and checked connections which were ok. So, I restarted the engine and gently tapped on the new iac. The rpms slowly came back to where they were with the old valve.

I did not lubricate the iac before installing and no telling how long it had sat in the parts store. Apparently it needed a bit of time to begin operating properly.

So, checking the connections to the iac and any others removed during the cleaning would be a good idea.

Best of luck.

Thank you for your post. I understand that there is a myriad of issues that could be causing this problem. I will look into some of the suggestions you have mentioned. Thanks.

The '97 is not common year for the intake manifold gasket issue. Even so it would not give you a redline RPM.

OP: You have a HUGE vacum leak. This can be from not puting the hoses back on the throttle body, or you have not connected the Idle Air Control valve back up.
Another thing to check is that you put the gasket back on properly. Spray around the throttle body with some brake cleaner to hear for leaks.

Watch this and see if you can find any mistakes you made:

http://www.youtube.com/watch?v=ApNTQs6GzcY
http://www.youtube.com/watch?v=qT7yA2TL4lk
http://www.youtube.com/watch?v=u3dC0ZLvpt8
Videos by Richpin :)

Thanks for your help guys. I cleaned up the solenoid that controls the air-flow bypass and my engine started just fine... idling at around 850. Thanks once again.

Thanks for your help guys. I cleaned up the solenoid that controls the air-flow bypass and my engine started just fine... idling at around 850. Thanks once again.


Sorry for bring this back to life, but I am having very very similar issues. So did you clean the IAC or something else?

If the car is warm or just been driven it will start right up. If it has been sitting overnight or a while at the store or work or something like that it will die if I just try to start it.

So to get it to start in this situation I have to give it WOT and it will start up. Once it starts up I have to give it some gas to keep it alive. As this happens white smoke comes from the exhaust.

After the car warms up this problem goes away and you can just start it right up.

Also the longer you drive it the idle seems to creep up. Once you put it in park or neutral it will rev up to 2500ish and if you let it sit it works it's way down.

Sound like the same deal? IAC? I'm going to pull it asap, just wanted some input. Thanks in advance.

BTW it's a 99 SC2 SOHC with 143k.

Sorry to hear about your issues.

A couple of suggestions to help fix your problem.

1) If your water temperature gague goes up to normal operating temperature as soon as you start the car in the monring when its cold, then you need to change out the coolant sensor ($14)

2) If your car is reving up to 2500ish for no reaon, than make sure that
- your throttle body is clean
- your bypass in the throttle body, where the IAC sits is clean
- your IAC is clean
- and you don't have a leaks in your gaskets where the throttle body sits on the intake manifold.


Other then that, that's as much advice as I can give you. They are all quite easy procedures to complete and besides the sensor won't cost you anything. Good luck!

Sorry to hear about your issues.

A couple of suggestions to help fix your problem.

1) If your water temperature gague goes up to normal operating temperature as soon as you start the car in the monring when its cold, then you need to change out the coolant sensor ($14)

2) If your car is reving up to 2500ish for no reaon, than make sure that
- your throttle body is clean
- your bypass in the throttle body, where the IAC sits is clean
- your IAC is clean
- and you don't have a leaks in your gaskets where the throttle body sits on the intake manifold.


Other then that, that's as much advice as I can give you. They are all quite easy procedures to complete and besides the sensor won't cost you anything. Good luck!


Actually now that you bring it up... My temp gauge doesn't move from cold ever... It's very odd. Here's what goes down:

Start the car and it's below cold.

Drive for 6 hours city or highway the gauge barely goes above the coldest mark. Now the car is obviously hot, the coolant is very hot to the touch.

If there is a traffic accident or such and I sit and idle for an extended period of time after the car is warmed up it will move up a tiny bit more, almost to a little below normal operating temp. At this point the relief for the radiator pressure starts releasing and my car starts steaming... Seems odd. Might be that temp sensor you spoke of?

replace your Engine Coolant Temperature Sensor. PCM uses this for idle control, and fuel mixture. When you hold the pedal at WOT you shut off the injectors. Since your ECTS is cracked sending bad data to the PCM, the PCM is making the mixture extremely rich. Replace it and you should be good to go.

There you go... $8.99:

http://www.autozone.com/selectedZip,36203/initialAction,partProductDetail/initialpartType,00113/initialR,APP222411/initialvehicleId,2538901/shopping/selectZip.htm

There are some instructions to it from the website if you run into any problems. The sensor should be easy to replace (at least it was in mine, which sat on the right side of the engine block about 6 inches from the top, with a wire sticking out of it.)

I am pretty sure that you have to drain your coolant before you screw out the sensor, but that is a fairly easy procedure as well. If you want us to describe you how to do that just let us know. :) Once again, hope it solves your issue!

Your problem sound eerily similar to the problems my 98 SL recently had. I replaced the TPS, still had the problem. I noticed my temp gauge was barely coming past the cold mark even though I knew it should be fully warmed up and was hard to start when cold. I replaced the ECTS and that did it. Now it idles around 600 rpm when warm, starts fast when cold, temp gauge responds like I would expect and it went from 25mpg to 31mpg. Basically the old ECTS was telling the computer it was freezing cold so it gave the engine a rich air/fule mix which killed its mpg and a high idle.

I am pretty sure that you have to drain your coolant before you screw out the sensor,

There is no need. Youll lose about 2 oz if that as long as you do it when the car is cold. If the engine is hot, the fluid will burst out and burn your hand :(

Ok so I replace my ECTS and it fixed the starting problem and the gauge now works.

A new problem has risen, I also decided to clean out my IAC because someone mentioned that as well. It was very very dirty and looks much better now. My car idles at about 600 as stated above and starts right up. I get a engine code now, P1404, an emissions code. We reset it and it still comes up. I get a slightly rough idle at stop lights and such.

Also my car will get pretty hot now when sitting in traffic and at lights. I've noticed my fan doesn't run unless the AC is on. Seems odd that no matter how hot it gets the fan wont kick on.

Thanks for the help.

You state you have a SC2 SOHC. This is not a car produced by saturn unless you did an engine swap. You have either an SC2 with a DOHC or a SC1 with a SOHC. Its important to determine which you have as it will enlight or eliminate certain issues.


DTC P1404 Exhaust Gas Recirculation (EGR) Closed Position Performance

Remove and Clean your EGR valve. The pintle should move up and down with no issues.

Your fan should come on about 3/4 as per the guage

You state you have a SC2 SOHC. This is not a car produced by saturn unless you did an engine swap. You have either an SC2 with a DOHC or a SC1 with a SOHC. Its important to determine which you have as it will enlight or eliminate certain issues.


DTC P1404 Exhaust Gas Recirculation (EGR) Closed Position Performance

Remove and Clean your EGR valve. The pintle should move up and down with no issues.

Your fan should come on about 3/4 as per the guage


My bad it's a SC1 then, it has the SOHC from the factory with the third door and such.

So I just need to clean that valve up?

remove it and clean it good. Start the car with it off with a rag over the two port holes. this will shoot any access carbon in the passages out.