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Old 06-07-2005, 10:42 PM   #1
Another91sc
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Default 91SC Running Rough @ Idle & Acceleration

I have a 1991 SC DOHC (original owner) with about 180k+ miles on the odometer, all emission items were replaced 2 years ago and the car has been running prefect up until last week when I started my car early in the morning to goto work.

When the car is cold, on startup the idle is higher than normal - around 1300rpm. Again at idle the oil pressure gauge reads 3/4 and the whole car has a vibration, to the point the pop-up headlights, steering wheel and hood are visibly vibrating. When driving the car I can feel as the RPMS increase the vibration remains pretty steady - the whole time the oil pressure gauge reads about 3/4. After about 15 minutes of driving the car, coming to a stop the vibration is still present but slightly reduced - the oil pressure gauge will read slight above 1/2. Sorry to keep to mentioning the oil pressure but typically when I come to a stop I expect to see that gauge read right at 1/2.

I've pulled plugs, checked for leaks in hoses etc... and I'm pretty much at a loss. Aside from the car vibrating everything appears perfect, not one drop of oil on the ground or smoke spewing out the muffle - no check engine light, nothing at all.

Any ideas ? Thanks......
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Old 06-08-2005, 05:55 AM   #2
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Default Re: 91SC Running Rough @ Idle & Acceleration

I'm going to go out on a limb here and suggest that the problem may not be related to oil pressure at all. It may be mounts. The torque axis mount (upper motor mount) in particular. There have been posts that when that mount is replaced, the lower transmission mount should be replaced as well. There are instructions on replacing both of these in the How-To section of this forum.
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Old 06-08-2005, 08:01 AM   #3
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Arrow Re: 91SC Running Rough @ Idle & Acceleration

The 91 Model year doesn't have an upper motor mount at all. It was added in the 1992 model year becuase there was the excessive vibration from the engine bay and engine.

I would suggest checking your lower mounts. There is a type of engine cable that holds the top part of the engine in place, but I am not sure where it would be located. I would have to do some research in my FSMs. You may want to check your ECTS as well. The ECTS (Electronic Coolant Temperature Sensor) is a very common problem of going bad on all Saturns becuase they are made from Plastic and can break easily tricking the computer into thinking your car is running cold when it is actually warm, which may explain the higher RPMs at startup.


Check your lower mounts and your change your ECTS, you can get the ECTS from the dealer and it is a new brass tip type for about $20. You can replace the ECTS in about an hour tops if you are mechanically savvy, check the boards in the how to section. As for the Oil Pressure Gauge, I have heard from my saturn mechanic that some of them didn't read the oil pressure all that well, which is why they were discontinued after the late 1991/early 1992 model year. I wouldn't let the Oil Pressure gauge worry you at all. As long as you have been keeping the oil changed you shouldn't have any problems.

Hope this helps.
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Old 06-08-2005, 08:35 AM   #4
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Default Re: 91SC Running Rough @ Idle & Acceleration

Thanks for straightening me out on that 2nd. I have read that about the '91s just forgot.
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Old 06-08-2005, 08:38 PM   #5
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Default Re: 91SC Running Rough @ Idle & Acceleration

I replaced the ECTS back when I replaced all the worn out emissions items, your right though - it was a pretty simple swap.

Today when I attempted to leave the office the battery decided to take its last breath, so I had to get a ride home from a co-worker.... I'm just thankful it happened at work rather than on my way home. I'll install the new battery in the morning.

I'll check on the lower mounts this weekend, I'm pretty sure its been a good 130k miles since those were replaced.

Thanks for the suggestions
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