2002 Saturn SL1 RPM shoots up when decelerating

Tiny
JJTHAUT
  • MEMBER
  • 2002 SATURN SL1
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 82,000 MILES
While driving at a cruising speed, the engine is about 3000 rpms. When I take my foot off the gas pedal, to slow down or put my foot on the brake to come to red light or exit the freeway, the rpm gauge starts to decrease to about 1900 rpm or idle, but then mysteriously shoots back up to 3000. Also, when parking the car, I will put the gear from drive to park and the rpm will shoot to 3000 rpm and just sit there revving itself. This happens sometimes. When in park and the car is having this episode, I have pulled the gas pedal towards me to see if it's stuck, and it's not. I have also stepped on the gas pedal to try to see if the rpm comes down, sometimes yes, sometimes no. Turning the car off stops the wild revving.

Gas mileage dropped from 35 to 29 consistently for 18 months now.

First, the check engine light came on and mpg dropped. Changing the front O2 sensor turned the light off, but mileage never came back.

Sine then, in my effort to return to my 35 mpg, here is what I've replaced:

Intake manifold gasket by mechanic (passed carb cleaner test 6 months later)
fuel filter (wix) (summer o8)
spark plug and wires (each 2x months apart)
1st pulled Autolites, put in Delco, the put in Autolite
cleaned EGR a few times with kerosene and carb cleaner, replaced egr gasket
cleaned out throttle body (Richpin06 youtube video)
replaced pcv valve (summer 08)
thermostat and coolant drain (april 09, engine runs hotter now)
engine coolant temp sensor (april 09, no different)
trans oil and filter (jan 09, no leaks)
air filter changed once a year
I have to put 1 quart oil in engine every 2000 miles.

Why is the mileage 27-29 mpg? It used to consistently get 35-37.
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Thursday, April 30th, 2009 AT 9:26 PM

4 Replies

Tiny
JACK42
  • MEMBER
If it is using 1 quart every 2k there may be something wrong internally in the engine. They shouldnt use that much oil. Has the check engine light ever come back on? What was the original code? I understand the o2 fixed it, but it may help figure this out. Check the fuel pressure regulator, remove the vacuum line off it and see if fuel is present, if so replace the regulator
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Saturday, May 2nd, 2009 AT 8:16 AM
Tiny
JACK42
  • MEMBER
The fuel mileage and the reving may not be related. Since it isnt storing a code it may have a sensor that is working but is working out of range a little. The Idle air control motor can cause the high rpm surges you are talking about. Have you checked fuel pressure with a manual gauge to see if it is within spec and that it jumps up a few pounds when the engine is revved?
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Monday, May 4th, 2009 AT 12:18 PM
Tiny
JJTHAUT
  • MEMBER
No, the car doesn't have any codes. Which makes me think an electrical component is failing or a vacuum leak.

Is the "idle air control motor" a sensor I can look at? This part is called something different on my car, so I don't know what to look at. Throttle position sensor? MAP?

I don't have any knowledge of how to check fuel pressure. The car has to go to a mechanic for that. The only way for me to find the spec is to go the library and find it inside a repair manual.
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Monday, May 4th, 2009 AT 2:08 PM
Tiny
JACK42
  • MEMBER
Key on engine off fuel pressure should be between 40-55 psi. The IAC is mounted in thethrottle body, has a flat connector, usually right next to the TPS. A MAP sensor outo frange can also cause poor mileage adn idle issues due to the fact thePCM thinks you are on the gas when you arent. Sometimes th ecar needs to be on a scanner to watch the sensors to see what is working, but is out of normal operating range
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Monday, May 4th, 2009 AT 3:08 PM

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