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1998 Cadillac STS Fluctuating Idle. Bad Gas Mileage

Tiny
JRC9009
  • MEMBER
  • 1998 CADILLAC STS
  • V8
  • FWD
  • AUTOMATIC
  • 175,297 MILES
The car has the 4.6 dohn 32 valve northstar engine. I pulled into a parking lot, shut it off. IT was running fine at that point in time. I started the engine after about 2 hours, and the service engine soon light was glaring at me, while it had not been before. The engine would race and then go way down to almost 500 rpms. Where as normal idle is 700 rpms. The car has started to drink a huge amount of gas going through town now as well. So the idle goes from 500 to about 1100 rpms. With almost 0 miles per gallon through town. IT does it in park and as well as drive when stopped. Is it the MAF sensor? The car normally gets 12 mpg through the city, and now I can watch the gas guage drop every few minutes.

Please help?
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Saturday, October 11th, 2008 AT 11:57 PM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi:
It could be any number of sensors causing the problem. I recommend taking the car to a nationally recognized parts store and have them scan it for trouble codes. Most stores will do it for free, and if the light is on and a code is storred, it will direct you to the problem. This will help you save money replacing parts that are good.

Let me know what you find or if you have any other questions.

Joe
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Tuesday, November 18th, 2008 AT 1:28 PM

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