Something might be loose... somewhere???

Alright, I know this has been asked and covered probably alot, but maybe I cant word my search right. So, please dont flame me too bad. I have a 90 Laredo that I just dropped a rebuilt longblock in. If I remember right, this problem was starting to surface when I parked it about 5 months ago. Here is the deal. It turns over and fires great. Idles like a singer sewing machine and has more torque and acceleration than I need. However, once I hit cruising speed, regardless of what speed that is, after a few minutes of holding the throttle steady, I can feel the motor surge and drop just a little. The rpm gauge is showing it bounces about 3-400 rpms in either direction. It is not constant. It will settle for a few minutes, then do it again. I have noticed that if I hit a hard bump, or Im on a section of rough road, it seems to be worse. Anyone have any ideas? This is very annoying, plus Im sure its not great for my mileage, with it surging like that. Thanks ya'll.

Defroster-A/C compressor is on and cycling?

loose wire bouncing around

no A/C compressor ... what system would have a loose wire, that would cause a change in rpms?

sounds like the tourqe converter is unlocking on your aw4.. for some reason.

there is a writeup , you will have to search.. that will tell you how to put some toggle switchs on that will allow you to unlock/ lock torque converter, and even select gears if you want.

check your tranny connection maybe the connecter is dirty or not making good contact.

Hmmmm, thats a thought. So where might I find the transmission connector?

I would agree with the converter. Since the tranny is computer controlled any tranny shop can plug into it, drive around the block and see if it is throwing codes.

Devil_Mutt said:

Hmmmm, thats a thought. So where might I find the transmission connector?

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on my 97 comes up on the passenger side, there is like four connectors in a bundle. yours is probably in a different area. see if you can find that write up.. it may point you in the right direction as far as a wiring diagram.

you might not see codes on a converter lock issue... but i bet dollars to donuts that is what your feeling, the converter unlocking for some reason.

would that cause a surge and drop in rpm's. What i mean is lets say I'm cruisin at 2000 rpms. All of a sudden it jumps to 2400, the settles back to 2000. Then it may drop to 1700, the return to normal.

Unplug the TCM and drive it shifting manually. If the problem goes away you are on the right track. If the problem persists, look to the power/grounds, TPS flat spot.

joe_peters said:

Unplug the TCM and drive it shifting manually. If the problem goes away you are on the right track. If the problem persists, look to the power/grounds, TPS flat spot.

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I'll give that a shot

Well, I got under the hood and started unplugging and plugging any and all connector I could find, from the front to the back. Also, I had read on here somewhere about the switch on the brake pedal had something to do with the unlocking of the torque converter, so I took it off and looked at it. Not sure what I did, but the problem seems to have stopped. Guess it pays to start with the easy stuff. Question. On my 90 model there is a small round thing mounted to the fender directly under the coolant bottle. It has 2 wires and a rubber line that runs into metal lines right next to the evaporator. It had a badly frayed wire, so fixed that too. Lastly, if all of the A/C components have been removed, do I need to keep the evaporator canister there? Is it used by any other system onboard?

Are you talking about the grey charcoal canister, or something associated with the AC system?