so i use my mom's mdx for moving hot tubs.

long story short i'm driving on the highway and in 5th at cruising speed the rpms go up and then down. it does it subtly but it jumps up like 3-400rpms and then stops. then will do it again like 50 seconds later.

is this the tranny going or what??

Car has 170000KMS

please let me know what you think everyone. As this is the vehicle that makes the $$$..

Your advise is superbly appreciated.!!

 

What year?

 

2002

 

Could be a bad transmission. That model year was known for them. Have you tried changing all the fluids to see if that helps at all?

 

no i just found this out less than 20 hrs ago. I prolly wil do that b4 i get her rebuilt..

thank god i got a guy who does it on the side for like 1600

 

Definite hydraulic issue. Your AT is probably fine. I actually had similar issue while in 5th. Changed out my 3rd & 4th pressure sensors on my AT and it hasn't returned. The 4th gear pressure sensor is one of the inputs to the shift & hydraulic control logic for the AT so it might have something to do with the spotty RPM's while cruising. Changing them out on the 01-02 MDX's is a breeze.. just pop the lower weather guard below the bumper on the driver's side. The two sensors / switches will be accessible. Each costs about ~$35, you'll need new washers / gaskets, some shop towels, 22mm 6 point socket & ratchet and about 5 mins. You don't even need to raise the front.

 

and how do i know they are shot b4 replacing them?

 

They don't usually completely fail. You could test them through the diagnostics port with a HDS and then pull them to test the resistance values. There should be a range to know whether they're in spec or not.. I don't have the equipment to perform a proper diagnostics and I wasn't going to pay $150 diagnostic fee.. so I paid $70 and just replaced them myself. They supposedly go out of spec and don't completely fail. Sometimes a DTC will pop up showing one has failed but it's been reported that an out of spec sensor usually wont throw a DTC until it's too late.