1991 Oldsmobile 98 idle / gas mileage

Tiny
ROYLULOFF
  • MEMBER
  • 1991 OLDSMOBILE 98
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 188,000 MILES
Dug into it and found the wiring was bad to the crank and cam sensors. Fixed that and it ran but still had problems.
Found the magnet on the cam had fallen off so the sensor couldn't read. Had that fixed and at that time changed:
timing sprocket set, new magnet, water pump, spark plugs, fuel filter, front motor mount, coil pack and module, O2 sensor.

Car ran good for a bit and the "check eng" came back intermittently. Scanned again and O2 came up again. Changed under warranty. Stored the car over winter and when I got it out it seemed to work fine. Drove it awhile and it got up to 25 mpg on the highway. (AUG) Then after that it started to go down hill fast. The last fill up I got 13 mpg. I understand my commute is very short and that would effect mileage but not this badly. Also the idle drops and comes back up sometimes so violently that the car will die. This happens when not under load in park or neutral.

Seems like when you first start the car it runs OK but as it warms up it starts to have trouble. Reminds me of an older car with a carb that the choke is sticking. I know the O2 is not really in the mix at first, the computer tells the car what to do but after it is warm it runs real rich and it would seem to me like it would try to lean out the fuel ratio. I'm no mechanic so I'm relaying on what other mechanics have told me and a Snap-On scanner.
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Monday, November 24th, 2008 AT 2:36 PM

4 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
Have you checked for new codes? Also, you may want to check the fuel pressure regulator. Also, the idle problem sounds like a throttle position sensor or MAF sensor problem. Have them checked.

Let me know what you find.

Joe
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Saturday, December 20th, 2008 AT 9:28 PM
Tiny
ROYLULOFF
  • MEMBER
Only code that popped was O2. O2 is only 1000 miles old but changed with Bosch unit. Ran good on way home but died the next day. Starts right up after dieing but still scary in winter. Have a blanket in the car incase I have to walk.

Fuel regulator has been check with gauge and seems fine. TPS work well per scanner and manually. MAF was ruled out by the mechanic but I really don't know?

Thanks for the reply and Merry Christmas!
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Monday, December 22nd, 2008 AT 8:25 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi:
I hate to say it but if everything checks out ok, there are only two choices. First, start replacing parts until you hit the rught one (very expensive, a waste of money, not recommended). Or second, wait until the problem happens and the car refuses to restart. That way a mechanic will be able to pinpoint the problem.

I hate to say that to you, but I don't see any other choices at this time. Let me know if things seem worse or other problems begin.

Merry Christmas,

Joe
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Monday, December 22nd, 2008 AT 3:04 PM
Tiny
ROYLULOFF
  • MEMBER
Yeah that is what another mechanic that has been scanning it said too. "IF it was broke worse" we would be able to figure it out easier.

I've been saving my quarters to take it to the dealer for a scan / quote. I just dislike dealers because it seems like they don't want to help the guy that has the old car they pressure you into buying new.

If I could afford new why do they think I drive this old one.

Appreciate it. Roy
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Monday, December 22nd, 2008 AT 3:14 PM

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