1990 Chevy Lumin Engine/Tranny Problem?

I have a 1990 Chevy Lumina with a V6 3.1 liter engine, and recently its been having a rough idle, and when u give it gas, its rough and hesitates, and the car can not go past 45, once it reaches that speed it just shakes when u give it gas, wont go faster, and when i stop and it downshifts into first, theres a rough jerk as it downshifts, its an automatic trans, and i dunno what the problem is, i think some trans fluid is dirtly and clogging something, but im not sure, any help would be great

start with a tune-up. Service Engine Soon light on?

did a tune up, new plugs and wires, everything LOOKs good, all tht we could do for a tune up was done, service engine light is OFF

Hmmm. this isn't my area of expertise. What comes to mind first is EGR passages are clogged or an injector being bad.

are you getting spark to all 6 cylinders? could be a coil pack (thus making it only run on 4) bad too.

There seems to be a spark on all 6. i took a spark plug wire and an old spark plug and held it to ground. there are many sparks on all cylinders so im pretty sure thats fine..not sure what else it could be

Make sure the MAP sensor has a good vacuum supply, sometimes the old line gets soft and collapses with suction or splits, and the MAP can't do it's thing. Makes 'em run like shit, like you descibe. Replace it if there's any doubt.

The vacuum lines to the sensor look fine. and they all have a suction on them...i'll take a look at the entire lines, and maybe check out the MAP sensor, what is that sensor by the way and what does it do

MAP (manifold absolute pressure) tells the computer what the level of air pressure or vacuum is currently in the intake, allowing it to figure how much fuel is needed to burn clean. I don't think your year had MAF (mass air flow) yet, which allowed them to directly sense the volume of air entering the engine.

Both would make them run really awful if they go bad.

Rereading, it does sound more like something a bad coil pack would do.

MAP and MAF issues usually involved stalling and really hard hesitations.

You get any intake backfire when you try to stomp it? Does it feel like it's trying to pull through it, or clear out, or just go flatter when you stomp it? Any smoke?

what do u mean by stomp it. like plug up the vacuum tube or what?

No, just when you press the gas down harder and try to get it to go. Does it feel like it just gets worse the more pedal you give it? Does it ever give you any backfire "woofs" through the intake?

I really think you've got spark breaking down under load. How old are the plugs and wires? Ever replaced coil packs or module?

i had a 1995 lumina that had similar problems turned out to be the catalytic converter.

That's possible. A vacuum test could spot that quick.

sounds like you have a bad coil pack,look at the coil packs and see if you see any green corrosion around any of them.Get a test light and ground each one out to really find the right one.you may want to replace the wires after that,they probably need changed anyway.If your check engine light is on,and the car is stalling,code 42,it would be you have a bad module.My car ran great no miss but was stalling,popping, for weeks but would start right back up,and run fine.then finally i got a check engine light.It was the module.