1998 SLS HIGH rpm at idle problem

[Greg McDonnell]

Hi guys,

My '98 SLS has just a little over 40K on its odometer and sits more than it is driven.  A few months ago I got my mechanic to change the spark plugs and wires (original from the factory).  At first it ran beautifully but lately when I start it the engine races (sometimes as high as 2,000-2,500 rpms!).  I took it out for a drive this evening and could hardly keep it stopped at a light!  The rpms were going from 1,000 to 1,500 to 2,000 as I sat at the light-no kidding.  I took it out on the interstate and it virtually drove itself-the rpms were that high!  It scared me so I got off the interstate and drove home on city streets.  The rpms were very high and when I pulled in my drive, it was all I could do to get it into park.  When I turned the engine off, the rpms were up near 3,000! 

What in the world is going on?  Will resetting the computer help?  I'm not sure I even want to drive it to a nearby GM dealership for a diagnosis and service with the rpms racing that high...I may have it towed!

Greg McDonnell
CLC#20841

[Greg McDonnell]

UPDATE:  I took the SLS to a nearby GM dealer for a diagnostics check on their computer.  It turned out to be the throttle control sensor that had gone bad.  I guess it was time for the darn thing to go as the car is 10 years and some months now.

Cost?  $233 part and labor
Car runs fine now-

Greg McDonnell
   

[Rusty Shepherd CLC 6397]

Greg,
I'm glad to hear that you got your problem resolved...and relatively inexpensively, too.  When the first "unintended acceleration" claims started (most famously the Audi 5000), I wrote them all off as driver error.
Then I drove my godmother to the airport in her nearly-new '84 Sedan de Ville and was idling back into her garage, when the RPM's increased markedly for just a second or two as I was about half way in and the combination of my reacting quickly and slamming on the brakes and the idle returning to normal kept me from driving through the back of her garage.  The next day, I took her car to her dealer and they replaced the idle speed control under warranty.  I am now convinced (and your experience bolsters my argument) that any car with electronic engine controls can have completely unintended acceleration. Newer cars with "drive by wire" systems with no mechanical connection between your foot and the engine throttle are probably even more likely to present it.  The one thing that's working in our favor is the greatly improved reliability of automotive computers. Many of the early EFI cars would just stop and refuse to start; the first-generation Sevilles with the Bendix EFI system were notorious for that problem when they first came out and many people traded theirs in after being stranded repeatedly.

[Greg McDonnell]

Hi Rusty,

Yeah those rpms racing higher and higher really can scare the heck out of you.  I am GLAD to have the problem taken care of. 

As for the first generation Sevilles and their refusing to start, that happened to my '77 (Seville) but we were able to get the problem solved.  It turned out to be a combination of things-a clogged fuel filter that needed to be replaced, a split in the rubber hose at the auxillary fuel pump (replaced all rubber fuel lines), and the pump in the fuel tank not wanting to work.  The mechanic took a 2x4 and bumped the tank giving it a jar and off it went.  I am not sure how correct that last one was but it got it going again and saved the cost of pulling the tank!  I hope it doesn't leave me stranded one day! 

Greg McDonnell