Hi johnnyb,
From your post, it sounds like this has been an issue in the past, but now has gotten a lot worse. A couple quick thoughts:
1. Is your CEL (check engine light) on? Even if it is not “on”, if you have the ability to scan for “pending” codes, this could help.
2. Check your TPS (throttle position sensor) output. The TPS on this vehicle has two separate 3-pin connectors. I presume this is a dual monitoring system for the TPS. For either set of 3-pins, one pin should have a 5-V reference, another pin should be ground, and the third pin should be the “sweeper” pin for the TPS. There are a couple of ways (that I know) to check the TPS.
a. Scan tool with the ability to look at Live Data…however, we may not have this.
b. Voltage Test. With the connectors attached to the TPS, backprobe the connectors (I carefully insert paper clips into each one). With the DVOM (digital volt, ohm meter) on DC volts, and the key in the “on” position, identify the 5V reference pin and ground pin. The remaining pin in the “sweeper” pin. Usually at closed throttle, the voltage reading (between the “sweeper” pin and ground pin is either 0.5V or 4.5V. Again, with the DVOM set on DC volts and connected to the ground and “sweeper” pin, manually open up the throttle. The voltage should rise from 0.5V smoothly to around 4.5V at WOT (wide open throttle). Or if you have 4.5 V to begin with, the voltage should fall smoothly to 0.5 V at WOT.
c. Resistance Test. If you do not want to back-probe the connectors, disconnect the TPS from its electrical harness. It is always important to isolate any component from the electrical system if resistance testing will be performed. Again, with the DVOM set on ohms, monitor the resistance on the “sweeper” pin and ground pin. You are looking for a smooth increase (or decrease) in resistance as the TPS goes from closed to WOT.
Any abnormal jump in voltage or resistance, or complete loss of signal all together, indicates that the TPS has started to wear out. Replacement would in be order. A loss of signal by the TPS, especially to the computer while the car is running, could cause rough or complete shutdown of the vehicle. Keep us posted.