RPM is slightly higher at idle

[szvook]

This past week, on two occasions, I noticed that my exhaust sounded a bit louder when I stoped at a traffic light. This would happen after the car was driven for a while with a few stops at stores and while driving back home, stopping at a street light. While stopped at the light and with the exhaust sounding a bit louder, I noticed that the RPM was slightly higher than normal, maybe 100-150 RPM higher. After driving a bit more and stopping at another street light, the exhaust note and RPM would go back to normal and stay normal when I got home. This does not happen when the car is started overnight and driven for a while.

I’m thinking it might be a vacuum leak, or maybe the idle air control valve is bad, or the throttle body is a bit dirty and is preventing the plate from closing fully. I had the throttle body cleaned, as a precautionary measure 8 years ago and it wasn’t too dirty then and was working fine.

There are no additional weird sounds when the exhaust sounds louder and the RPM is slightly higher. No vibration in the body, in the steering wheel or the brake and gas pedals.

 

[szvook]

If the idle air control valve is bad, would pulling the codes identify it?

 

[gsxr]

There is no idle air control valve on the LH-SFI system. However, pulling codes would be a good place to start, just to make sure it's not an electronics issue. Next step would be a smoke test on the intake to verify there are no air leaks in the intake tract.

 

[ArauzMotoring]

This past week, on two occasions, I noticed that my exhaust sounded a bit louder when I stoped at a traffic light. This would happen after the car was driven for a while with a few stops at stores and while driving back home, stopping at a street light. While stopped at the light and with the exhaust sounding a bit louder, I noticed that the RPM was slightly higher than normal, maybe 100-150 RPM higher. After driving a bit more and stopping at another street light, the exhaust note and RPM would go back to normal and stay normal when I got home. This does not happen when the car is started overnight and driven for a while.

I’m thinking it might be a vacuum leak, or maybe the idle air control valve is bad, or the throttle body is a bit dirty and is preventing the plate from closing fully. I had the throttle body cleaned, as a precautionary measure 8 years ago and it wasn’t too dirty then and was working fine.

There are no additional weird sounds when the exhaust sounds louder and the RPM is slightly higher. No vibration in the body, in the steering wheel or the brake and gas pedals.

Does the idle bounce around a bit or just stable higher idle?

Do you try to clear it by turning the car off and on again?

I ask because occasionally, my car will have an erratic hot rod idle, and I either drive thru it and it’ll self correct (it happened once at least) or I’ll shut the engine down and re start and it drives smooth again..

Some research led me to think it could have something to do with the crank position sensor, but idk lol

 

[szvook]

Does the idle bounce around a bit or just stable higher idle?

Do you try to clear it by turning the car off and on again?

I ask because occasionally, my car will have an erratic hot rod idle, and I either drive thru it and it’ll self correct (it happened once at least) or I’ll shut the engine down and re start and it drives smooth again..

Some research led me to think it could have something to do with the crank position sensor, but idk lol

No bounce, just stable higher idle. Did not turn off and restarted the car while at the light, was just listening for any other noise aside from the exhaust note. While stopped at the light, the RPM would drop back normal after about 10 seconds.

 

[szvook]

When I first heard the louder exhaust while stopped at a light, I thought maybe a failing brake booster diaphragm might be the culprit and is creating a vacuum leak, but when it happened again, I looked at the tachometer and noticed the higher idle. The brake pedal did not feel any harder than usual. I will have diaphragm checked as well.