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Unstable RPM at 55 mph

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Old 03-12-2018, 07:46 PM
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Default Unstable RPM at 55 mph

It felt like the blazer had a miss fire as the RPM at 55 would jump between 1800 and 2000 at first and then it started to act in a similar fashion at other speeds so I figured miss fire. There is no code being shown on the SES other than O2 sensors and EVAP so I doubt either of these are causing it.

After changing the spark plugs it seemed to run fine for a while, but as I was giving it a hard acceleration in bucked at bit (maybe just in my head). I need the car running good by the end of the week so I can get back to college.

There is also a new oil leak that has the entire bottom of the engine covered in a thin layer of oil. Never tried to fix these before, no idea where to start. Could this be causing the weird RPMs?
 
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Old 03-12-2018, 10:36 PM
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Originally Posted by LuckyAce View Post
It felt like the blazer had a miss fire as the RPM at 55 would jump between 1800 and 2000 at first and then it started to act in a similar fashion at other speeds so I figured miss fire. There is no code being shown on the SES other than O2 sensors and EVAP so I doubt either of these are causing it.

After changing the spark plugs it seemed to run fine for a while, but as I was giving it a hard acceleration in bucked at bit (maybe just in my head). I need the car running good by the end of the week so I can get back to college.

There is also a new oil leak that has the entire bottom of the engine covered in a thin layer of oil. Never tried to fix these before, no idea where to start. Could this be causing the weird RPMs?
Fluctuations in RPM at that speed sounds like it's trying to go into overdrive but isn't for some reason. Have you checked your transmission fluid lately? Should be red in color, not burnt smelling, and in the crosshatch section of the dipstick at normal operating temperature in park.
 
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Old 03-13-2018, 11:32 AM
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Checked the dip stick at cold and it was still red and didn't smell burnt it was also slightly above the cold mark (within the cross hatch portion). I changed the fluid, filter and shift solenoids about 20,000 miles ago (dropped the pan twice). At the time there was nothing alarming in the pan and the old fluid was still red (although fairly dark).
 
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Old 03-13-2018, 01:04 PM
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Just took it for a longer drive and the issue is getting worse. I checked the fluid level at the end of the drive but in direct sunlight I had trouble seeing red, I could tell that the stick was wet.

It will be jumpy at anything over 50 mph, but pretty darn stable below.

I read online about the vehicle speed sensor and throttle position sensor could cause this. Would these be a good spot to start?

Can I test this by taking my Father's TPS from his 2000 S10 and putting it in for mine? He has a 4.3 v6 in his truck too. Pretty sure it is the same engine
 

Last edited by LuckyAce; 03-13-2018 at 02:17 PM.
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