I've tried to figure this one out but I really can't narrow it down. The minivan randomly bucks and most of this is done on the highway. I think it's actually a combo of a couple of problems. One of them I think is torque converter related. When on the highway going 65mph or higher the van bucks like it is trying to shift around (3spd rebuilt auto, not original auto either). It sounds like the torque converter is unlocking and you can hear the engine rev up a little. I think this could be tweaked by adjusting the kick down cable. That is only part of the problem. It also has a problem where it bucks kind of hard at random. For some reason it did alot of this hard bucking this afternoon and the check engine light came on. I stopped by autozone to get the code read but they couldn't because it didn't have the connector. Apon leaving the light went out.
About 3 weeks ago I attempted to fix this bucking problem by replacing the plugs/wires/cap/rotor. The plugs were all worn to about 0.070", rotor/cap were so bad that I'm suprised that they still worked and it seemed like the #4 plug wire wasn't hooked up correctly or at all. This did nothing performance wise but make my wallet a little thinner. You can hear the idle surge a little bit (like 100rpms tops) and to my suprise it runs the same. When the car is cold/warming up I notice that when you first hit the gas the engine bogs a bit and then takes right off. If you give it some pedal it runs strong for a van with 137K on it.

Any imput would be appreciated,
Matt

 

I forgot to mention that I checked into the speed sensor problem. I unwrapped the speed sensor wires down by the sensor connector to figure out what white color was the sensor output. Same color pattern as my neon, Orange 8V supply, Black/Lt Blue striped Ground and White/Orange striped sensor output. I traced the wire back up by the fuse box and tapped into it with my Digital MultiMeter. With the car idling in D (jacked up) I couldn't find an issue so I took it a step furthur and hooked up the Oscilloscope. Couldn't see an issue with the sensor output. The only problem that I picked up was a 8KHz 15mV signal running on the wire. It changes with rpm and I think it's just noise from the alternator.

So today I took it out and after about 20 minutes I realized that the van wasn't acting up anymore. Not a problem all day. I did get ahold of a neon buddie with the sensor/connector off my parts car. I plan on getting that back and when the van starts to act up again i'll replace the connector. AFAIK the sensors the same, some model year neons had a different connector (I think newer ones). The only difference between the MTX and ATX sensors is the actual gear which you can just take off and swap with the correct one.

 

Try pulling the error codes off the computer using the key on-off retrieval method.

 

Is it the same as the 1st gen neons worked? On/off 3 times and count the check engine light flashes? Is there someplace that lists the codes? BTW It still runs good.

 

I had a similar problem and it was with the torque converter lockup solenoid. You can change this solenoid yourself if you take the trans pan off and unbolt the solenoid and pull it out. Lists for about $40 (without the new pan gasket , filter and fluid)
Test this by unpluggin the solenoid before taking it out. You will see the connection near the dip stick hole on the drivers side forward edge of the transmission.

 

Possibly a poor connection with the lockup solenoid? AFAIK it works but it just randomly bucks. I did get a code one day when it was bucking pretty bad, it was for the throttle position sensor however it measures fine. If I could find the ecu in the van i'd check the signal there rather than the sensor to check the wiring harness...