Erratic Idle and Stalling in '95 3100 GP!!!

[95grandprix3100]

Hey guys, I haven't posted in awhile but my car is just now having some crazy issues. The issue is only when I start the car and the rpm immediately starts bouncing up and down and just idling erratically. If I try to rev it, it seems to bog down and if I'm lucky will start to jump up to where it is running at the right RPM but only if I'm keep it rev'ed. As soon as I release the throttle it goes right back to idling erratically. If I put it in drive at any of those points the RPMs drop way low and continue to bounce. If I apply any gas at that point it will just bog down and stall. If I don't give it any more gas in drive the RPMs will continue to drop until the car stalls. After the car has stalled it becomes impossible to start again usually for an hour or so. The best I'll get is it will start and run for about 4-5 seconds.
The strangest part of this is that 4 out of 5 times that I start the car none of these symptoms appear. If I start the car and the idle is fine I can drive it for as long as I want without having a single issue. Even if I let it idle for 20 minutes or so when it hasn't shown the symptoms it will continue to run fine. The car will only stall when immediately after start up the RPMs bounce up and down.
My Mechanic told me that it is my fuel pump but that doesn't make any sense to me because when the car is started and runs fine it will drive great the entire time I'm driving until I start it and the idle is erratic. Even under full throttle the engine revs and shifts great.
The fuel filter was recently replaced because it was thought to be the issue along with the fuel line that connects to it. My car isn't giving me a check engine light and I can't check for codes since its a '95 (gay!) unless I pay an actual mechanic to diagnose it. I really don't want to toss any more money into it since I'm selling it this summer to help pay for tuition and really need your guys help. I keep thinking it must be a bad sensor, but you all are the real geniuses with these engines. Any help would be greatly appreciated.

[95grandprix3100]

Just to add before anyone asks It has almost new AC Delco spark plugs and brand new Bosch premium wires. I checked the vacuum and rattle on the pcv valve and both were good. I did a head gasket job and noticed this issue about a month of driving after the head gasket job.

[Tbay99Venture]

Idle air control OK

I'm assuming that car has an idle air control valve in the throttle body. Maybe it's binding up on occasion? If you take it out don't activate the key or it may extend itself too far for you to get it reattached. The symptom I had ('99/3.4L) was that the car would start OK but then randomly quit at idle and we could tell the idle speed wasn't always right. The valve is a sort of jackscrew driven poppet and the threads were stripped. They aren't cheap enough that you would want to just buy one and try it out.

[3400-95-Modified]

Actually the 95 can be read with an OBDI reader, so its not specific to 95 that makes it GAY, its GAY that auto parts stores don't carry OBDI tools.

If you have a spare I recommend swapping out the tps as a test

[95grandprix3100]

I went and picked up a tps sensor and popped it in but the new sensor had no effect. when I first started it up it was runnning fine and I had no issues until I took it for a quick spin around my neighborhood. As I was driving away from a stop sign the engine suddenly cut out down to about 800 rpm and no matter what I did it would not respond. I found that the rpms would jump up a little if I pushed the gas all the way down and then let completely off. Every time the pedal reached its resting position the rpm would jump for a second and the car would surge forward. This went on for about 2 minutes and then the car started running normally. Later on I had to keep starting it and shutting it down to even get it to start doing the problem. When I finally did get it to do the problem I did my best and was able to keep it from stalling while in my garage. After almost 20 minutes of running poorly it finally threw on a check engine light. So I don't know if it is throwing codes or not when the light is off.

[robertisaar]

the engine suddenly cut out down to about 800 rpm and no matter what I did it would not respond. I found that the rpms would jump up a little if I pushed the gas all the way down and then let completely off.

seriously? you had to go full throttle and the engine STILL didn't respond until you let off?

serious fuel/spark issues?

[95grandprix3100]

I don't know but it was acting like it didn't even know that the throttle was being pressed down. That was the first time that has ever happened, but it was pretty scary going less than 10 miles an hour in the middle of the street. The closest place I could pull over in was on a huge hill. Surprisingly it managed to make it up the hill and into a church parking lot to where it immediately started running great.

[60dgrzbelow0]

Just in case you crimped anything when under there before... Have a look around all the harness and sensor connectors for pulled or damaged wiring... pull the connectors off of the IAC and TPS Throttle Body sensors and see if something is loose and then plug them all back in nice and snug... Didn't Ben mention something a while back about "turning the TPS Potentiometer insert 180 degrees out..." as a possible problem that would present with these kinds of symptoms?

[Tbay99Venture]

TPS live testing

OK, maybe I'm getting a little too ghetto tech here but if he backprobed the connector and taped everything up well he could run a lead outside the hood and in the window so it would be simple to clip on a digital voltmeter once the problem came back. If the meter follows the pedal motion at least he can rule out the TPS.