I've got a 2003 Yukon Denali XL with 238k miles. Last year when driving on the high way at 70mph I would notice the rpm's moving between 2500-3000 every few seconds. I could hear the engine surging. Holding the gas at same positing this would happen at speed.
I also noticed that at slow speeds shifting between 2nd and 3rd wouldn't happen unless I lifted off the gas. Otherwise It would rev up past 4k until I lifted then it would shift. Was kind of like driving a manual transmission.
At that time the car would often go into limp mode (reduced engine power) at startup and would have to be started multiple times to get rid of that message. At one point last year I pulled the entire throttle body and cleaned it. There was a heavy dirt/grease build-up at the bottom of the intake. That seemed to fix the reduced engine power message. It also seemed to make the 2nd - 3rd shifting problem get much better, but over time it went back to it's old state (having to lift off the gas).
This past weekend we went from NJ to DE and MD and back and I noticed that on the highway at 60 mph and above I was at 3000 rpm. 70 mph was like 3200 rpm and 80 was a full 3500+ rpm. That seemed way to high and I started wondering if the trans was going into 4th gear.
This weekend after a lot of Youtubing and fretting over having to have transmission work done, I saw a post about replacing the throttle position sensor. This truck has the 6 liter V8 and as such has the throttle sensor pop riveted to the side of the throttle body unlike the simple screw on type.
I ordered and installed a Dorman replacement (BTW, 58 bucks on amazon, 110 at auto parts store) tonight and took it out for a test drive. I also disconnected the battery after installing the new sensor. Gears inside of housing all looked fine.
Right away I noticed the 2nd to 3rd gear shifting problem was all but gone. Shifts were smooth. It also seemed like speeds up to 60mph were not running the rpm's up to 3000 like it had before. Speeds about 65-80 did have rpm's right at 3000. That still seems high. No wavering rpm during cruise at 60+ but that didn't happen this past weekend either.
What I did notice was coasting down hill at 70 (foot off the gas) the rpm would go down to 600 and waver between 600-1200rpm every few seconds. Seems like there is still a problem.
What I'm seeing is rpm's too high at 65+ and this wavering rpm when coasting. I'm starting to wonder if the new throttle positing sensor actually did anything, or if disconnecting the battery reset an ECM and all problems will return.
No strange noises from the transmission, it's been pretty rock solid. Never towed anything with this truck, it's Mom's actually.
This one is real strange and I'd like to solve it so I can try and get 300k out of it. Body & motor are both holding up pretty well at this point.
Any insights?
Possible broken wire?
VSS (Vehicle Speed Sensor)?
Does throttle position sensor need to be calibrated?
No check engine lights. I have an OBD II and I'm going to see if it will tell me what gear i'm in when cruising. It is more capable than the simple code readers.
Thanks,
Roveer
I also noticed that at slow speeds shifting between 2nd and 3rd wouldn't happen unless I lifted off the gas. Otherwise It would rev up past 4k until I lifted then it would shift. Was kind of like driving a manual transmission.
At that time the car would often go into limp mode (reduced engine power) at startup and would have to be started multiple times to get rid of that message. At one point last year I pulled the entire throttle body and cleaned it. There was a heavy dirt/grease build-up at the bottom of the intake. That seemed to fix the reduced engine power message. It also seemed to make the 2nd - 3rd shifting problem get much better, but over time it went back to it's old state (having to lift off the gas).
This past weekend we went from NJ to DE and MD and back and I noticed that on the highway at 60 mph and above I was at 3000 rpm. 70 mph was like 3200 rpm and 80 was a full 3500+ rpm. That seemed way to high and I started wondering if the trans was going into 4th gear.
This weekend after a lot of Youtubing and fretting over having to have transmission work done, I saw a post about replacing the throttle position sensor. This truck has the 6 liter V8 and as such has the throttle sensor pop riveted to the side of the throttle body unlike the simple screw on type.
I ordered and installed a Dorman replacement (BTW, 58 bucks on amazon, 110 at auto parts store) tonight and took it out for a test drive. I also disconnected the battery after installing the new sensor. Gears inside of housing all looked fine.
Right away I noticed the 2nd to 3rd gear shifting problem was all but gone. Shifts were smooth. It also seemed like speeds up to 60mph were not running the rpm's up to 3000 like it had before. Speeds about 65-80 did have rpm's right at 3000. That still seems high. No wavering rpm during cruise at 60+ but that didn't happen this past weekend either.
What I did notice was coasting down hill at 70 (foot off the gas) the rpm would go down to 600 and waver between 600-1200rpm every few seconds. Seems like there is still a problem.
What I'm seeing is rpm's too high at 65+ and this wavering rpm when coasting. I'm starting to wonder if the new throttle positing sensor actually did anything, or if disconnecting the battery reset an ECM and all problems will return.
No strange noises from the transmission, it's been pretty rock solid. Never towed anything with this truck, it's Mom's actually.
This one is real strange and I'd like to solve it so I can try and get 300k out of it. Body & motor are both holding up pretty well at this point.
Any insights?
Possible broken wire?
VSS (Vehicle Speed Sensor)?
Does throttle position sensor need to be calibrated?
No check engine lights. I have an OBD II and I'm going to see if it will tell me what gear i'm in when cruising. It is more capable than the simple code readers.
Thanks,
Roveer
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