I've read some of the previous posts about the 3.1 running rough and I'll try those... However, I didn't see anybody mention anything about fuel mileage taking a dive. Five bucks will take me to work and back, but with the car running this way the $5 bucks only took me one way. Does this help narrow down the problem? I'd like to avoid spending more money on sensors I don't need.

The problem is close to the others mentioned... It started fine this morning, then got rough after warm-up. Runs rough through idle and acceleration (gotta throw it into neutral and rev while at lights), reduced power, stalls when you let off the gas. I let it sit until lunch time to cool... running rough right from start now.

There could a lot of different problems causing it to run rough, but with the dramatic change in fuel consumption changing your O2 sensor(s) probably would be a good place to start.

If your coil packs have never been replaced you might want to check them also, a bad coil pack can certainly cause it to run rough.

What have you done so far for maintenance on the vehicle?
Spark plugs, spark plug wires?
I also second the coil packs but have you checked the spark plug wire connectors on both sides (spark plug side and coil pack side)? If the connectors are rusty, then definitely you need to clean those connectors.

I've changed oil, filters, plugs. Checked wire connectors and coils, all clean. Just replaced starter the day before this started.

I saw on a previous posting that someone mentioned the fuel pressure regulator. Is that located under the plenum?

It sound to me like a vacuum leak poss. in the area of the starter. I say that because you just replaced the starter the day before this prob started. From your desciption it would have to be in a part of the vac. system the becomes active after the eng is warmed up.

Mind you this is only a guess

When you find out how to fix it can you please post how you did it? My 94 with the 3100 is having the EXACT same problem and so i assume its the same thing. Im leaning towards O2 sensors but it looks wicked hard to change, especially in the winter w/ no garage. Anyone know how to just disconnect it so the car always thinks its cold?
any help would be appreciated. thanks

O2 sensor is not very hard to change, if it is in the same place as my 95 3100 it is on the firewall side of the engine on the drivers side. When my car was running rough I replaced plugs, plug wires, pcv valve, O2 sensor, cleaned IAC and throttle body and none of that worked so I gave up and took it to the shop and found out that a coil pack had gone bad. After having coil pack replaced (at about 120K miles) it ran fine for three weeks and then started acting up again (this time mainly just hesitation on acceleration) took it back and another coil pack had gone out. I read on another board that about 100K-120K miles is about average for coil packs.

Could be any number of problems from 02 sensor to clogged catalytic converter or a serious vacuum leak or even a coil pack. Have you checked the onboard computer for trouble codes? Do you have any access to any diagnostic tools to determine which cylinders are weak or misfiring?

Thanks for the ideas. I haven't been able to mess with it yet, but I'll leave a post when I find the problem...

O2 sensor is not very hard to change, if it is in the same place as my 95 3100 it is on the firewall side of the engine on the drivers side. When my car was running rough I replaced plugs, plug wires, pcv valve, O2 sensor, cleaned IAC and throttle body and none of that worked so I gave up and took it to the shop and found out that a coil pack had gone bad. After having coil pack replaced (at about 120K miles) it ran fine for three weeks and then started acting up again (this time mainly just hesitation on acceleration) took it back and another coil pack had gone out. I read on another board that about 100K-120K miles is about average for coil packs.

yea id highly suspect the coil packs to be the culprit. the only way to be certain i have found from personal experiences would be to remove one of the spark plugs, then connect it to the spark plug wire again but rest the bottem (spark end) of the plug to something metal on your engine such as the exhaust manifold or the head or something of that sort, just as long as its away from any possible fuel particles that might be ignited by spark. then have someone crank over the motor a few times for ya, (keep in mind if its a v6 its a good idea to disconnect the plug wires from at least 2 more plugs because ive found that a v6 WILL start and run even without all 6 cylenders, heh. while the other person is cranking on the engine, look at the spark plug that is resting against the engine... if you see a white or bluish colored spark then your coil packs and wires etc are all fine and dandy. however, if you see no spark or a weak spark such as an orange or yellowish colored spark, then its most likely either bad coil packs or bad wires or plugs. my recommendation in that case would be to just replace all coil packs if urs happens to have more than one, replace the plug wires, and if you havent already, replace the plugs too. might be a little costly but trust me it would help prevent future problems as a result of some wires going bad or something like that... just simple preventative maintanence to consider. if however, you dont have bad spark, then i would start thinking about possibly either fuel pump or fuel filter... or try the O2 sensor(s) and such as the other guys on here have already suggested. but my guess is that its the coil packs and/or wires.

mike