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Help! Can't figure it out!

Hey everyone!

I have a 2002 Isuzu Rodeo LS, 3.2V6, 2wd 4speed automatic. The problem I’m having is that, sometimes as it shifts from 1st into 2nd or 2nd into 3rd, the RPMs will jump slightly (up to around 3000) and the whole car will lurch forward as if it doesn’t want to engage. The only thing I’ve been able to do that reduces this occurrence is to let off the accelerator at the exact moment it tries to shift. Also, when coming from a dead stop, sometimes it will shutter on take-off. I have no idea what is causing this.

Here is what I’ve been able to narrow down: The transmission is just over a year old, as is the torque converter. When this first started happening, I took it in to get looked at and they assured me the transmission fluid was in perfect condition.

The ‘check engine’ light has not come on, so that rules out any of the sensors going bad (TPS, MAP, EGR). I’ve replaced the sparkplugs, which were prematurely worn. The fuel pressure regulator is working fine as far as I can tell and I’ve run the STP fuel system cleaner without any change.

As of now, I can’t think of anything else it could be. Any ideas or suggestions would really help, as this is effecting my gas mileage by roughly 20%. Thanks!!

It’s the transmission, but just to clarify:

A year ago, was the transmission new, rebuilt, or used but new to you?

The transmission was rebuilt. And that’s not what I wanted to hear.

If it’s the transmission, would the shift modulator be the culprit? I know that was replaced on the original transmission.

I am assuming that you have checked the fluid level and that the fluid does not look black or smell burnt. If this transmission has a shift pressure control solenoid, it could be the area of the problem. I am very unfamiliar with this transmission. If it is a computer driven unit, have the TCM scanned for codes. A lot of TCM diagnostic modes allow a snapshot of the clutch transition parameters which may lead the transmission technician to the source of the problem.

So have a transmission technician look at the problem; do a TCM scan for codes; and give you a diagnosis.

Hope I have helped. Let us know the progress through this problem.

I just dropped it off to have the transmission looked at. They will run a complete diagnostic and do a fluid flush. I also told them to take a look at the accumulator piston seal, because that was the first issue I had with the transmission before it was rebuilt and was experiencing similar symptoms (NOT the shift modulator as I previously thought).

I have not checked the fluid, only because this particular transmission model has no dipstick and requires some fairly sophisticated machinery to change the fluid. It is the stupidest design for a transmission I’ve ever heard of and it probably the cause of 85% of the problems I’ve had with it (the fact that I can’t check the fluid myself).

I will keep you updated on the progress.

I just got it back from the transmission shop. They were unable to find anything wrong internally or with the fluid condition/level. No leaks, no abnormal wear in the pan. Diagnostics showed no codes. They replaced the filter and changed the fluid. On the test drive, they were able to experience what I’ve been trying to describe to them, which has never happened before. Which leads them to believe there is a defect in the transmission housing that they are unable to see with the naked eye. Which makes sense–about 3 months after I got it, I took a corner too fast and ended up in a ditch. The only visible damage was cosmetic, no leaks or bends underneath. But my guess is that as I skidded along in the ditch, something caught the housing and warped it to where no transmission will work right as long as that housing is used.

At this point, I feel good knowing everything is as it should be internally. But I’m not going to sink anymore money into it, even for a new housing or a factory re-man. Can you say ‘trade-in?’

Thanks for your help!

Did they do a line pressure check especially a line pressure check when the problem appears? Rereading you orignal post brings to mind a possibility that the pump is not holding pressure while the shift is occuring and when you launch from a stop. The shuddering could possibily be a stick/slip of a clutch pack but it also could be a weak one way clutch or sprague.

Anyway, it sounds like you have the solution to this problem as in “trade-in”.