I need some help. I am probably the worst person when it comes to diagnosing automobile problems so hopefully somebody can help me. I have a 98 Isuzu Rodeo Automatic transmission. My problem is I can only get up to about 20-25 MPH when the transmission disengages and goes into neutral. I then have to coast until the vehicle gets down to about 5MPH and then can accelerate once again to approx 20MPH. Not sure what the problem is but I brought into a local garage who flushed transmission fluid to no avail and told me he thought the transmission was gone. Should I just have the transmission replaced or could there be something else causing this problem. Any help or information would be appreciated.

Here is a dumb question. Is it in 4 WD? I had a similar problem when my 4WD was engaged, my tire were different diameters causing the drive train to bind, which would knock the transfer case out of gear. But when this happened you knew it because made and awful sound like gears grinding. This may be of no help, but it is the only thing I have personaly experienced.

Hopefully the place you took it to, knows how to check the level of the tranny fluid.

The only other thing that comes to mind is that when you are in D you get up to 25ish mph and then it bumps itself into N makes me think you have a dirty or bad range position sensor.

http://www.geocities.com/endre_rl/isuzufaq.htm#faq59

Like Ryan says, when it acts up, make sure the 'PRND321' lights on the dash stay in 'D' and are not jumping all over the place. If the dash gear indicator lights dont line up with the gear you have selected with the floor gear shifter, your range/mode sensor is bad & causing your problems. Can you shift it manually when it acts up?
G/luck
Joel

Like Ryan says, when it acts up, make sure the 'PRND321' lights on the dash stay in 'D' and are not jumping all over the place. If the dash gear indicator lights dont line up with the gear you have selected with the floor gear shifter, your range/mode sensor is bad & causing your problems. Can you shift it manually when it acts up?
G/luck
Joel

It is an automatic. Do you mean put it into neutral or reverse?? I wll check out the lights on the dash and see what they are doing. Thanks EVERYBODY for taking the time to give me some advice. Hopefully I can get to the bottom of this and get it straightened out w/o having to replace the whole transmission.

try ryans suggestion first if that does not help you pinpoint the problem take it to the dealer sounds like it may be the force motor solenoid in the valve body of the tranny I have replaced a few of those fofr similiar concerns

my girlfriend's passport is having the same problem, i promise you it is not the range sensor, and i have changed the fluid, to start off the transmission was working fine, and would randomly just go into 1st gear and flash the transmission light, you could shut it off and turn it back on and it would be fine, now it will not shift out of first gear when in any of the forward gears, period, 1st is all it does, no trans light, anything, the fluid was burnt and there were fine metal shavings, but i cant even get it to go into limp mode or anything, occaisionally if you really get going in d it feels like it shifts into neutral, i feel like even if the trans was bad it should still be trying to shift at least, or throwing a code, but i get neither, i dont know where to go from here, i have cleaned that range sensor, and the fluid is filled properly, i cant find any wiring problems, i'm stuck, any help would be appreciated, its a 97 passport 4X4 no grinding noises or anything, and reverse is fine, it just refuses to shift out of 1st gear

This same thing happened to me, and it eventually would quit catching gears. It broke down on the highway and the only way I could go was in reverse. I got a new transmission put in, but 2 years later I'm having a similar problem. No one can figure out the problem. It goes into drive fine, but when the car goes to shift you can feel the something slam very hard. The dash lights also go out prior to this happening. It doesn't do it every day and there is really no particular time of the day it will do. If you are still covered under warranty, I'd get a new one. Otherwise, I seriously doubt it will fix your problem. When I took mine in they tried to change the transmission fluid as well, which cost $120 and didn't help at all! I have come across a lot of people with this problem, I have yet to find an answer...

I would start with cleaning the shifter range selector.

i promise you it is not the range sensor, i have cleaned that range sensor, and the fluid is filled properly,

i thought i made that pretty clear that i already did that

Since we all have rodeo. can you keep us up to date on how you guys get it fix on this issue? I really like to know because just in case mine acts up like that. Please keep us up to date. Thanks.

on a 1994 rodeo is the throw out bearing on the motor side of the flex plate or the trans side