1996 olds 88 engine/transmission

Hi,
I bought a 1996 Oldmobile Delta 88 a few months ago, it has 240,000 km on it, and has the 3800 engine (non-supercharged).

Shortly after getting it, the check engine light came on, and later that day, after about an hour on the highway, a shuddering/shaking started. If I either released the gas, or gave it more gas, it would smooth out. It continued like this for a month or so, only doing this shaking after the engine was warm, and I held a constant speed for a while. The check engine light/MIL, will stay on for a couple hundred km's, then off for a couple hundred.
Shifting from OD to D/3 did not affect it.

Then, I started having problems accellarating. The car will have power for a second, then have no power, then power again, like it is hesitating. If the hesitating is very bad, the MIL light will begin flashing until I let off the gas for a while.

I have an OBD2 reader hooked into my laptop, it once reported the crankshaft position sensor, but if that was toast I'd expect stalling or hard starting, not this.
It also reports torque converter slippage when the light is on. From this I'd expect a hard 1st-2nd shift, but that has been fine.

Recently, when I first start it, it will run rough for a couple minutes, it doesn't matter if it's in gear or not.

Any ideas? It doesn't seem like the torque converter would cause all this, especially since it runs rough in park. I've changed the fuel filter as a first step already, thinking of doing plugs/wires and coils next, but would prefer not to waste money if someone has a better idea.

Check your fuel pump. I had one go in my '91 olds 98. The car would run fine for a while til the pump got hot then start missing/intermittently losing power. Also caused the transmission to go nuts shifting and hunting for gears since it can't understand why the motor keeps losing power. Also check TCC clutch switch and solenoid

Check your fuel pump. I had one go in my '91 olds 98. The car would run fine for a while til the pump got hot then start missing/intermittently losing power. Also caused the transmission to go nuts shifting and hunting for gears since it can't understand why the motor keeps losing power. Also check TCC clutch switch and solenoid

Thanks for the reply,
That is a good idea, I actually wanted to check that, but it appears this car does not report fuel pressure to the OBD2 system, as it always reports "No Data".

Maybe I can have a shop check the fuel pressure for me.

Thanks for the reply,
That is a good idea, I actually wanted to check that, but it appears this car does not report fuel pressure to the OBD2 system, as it always reports "No Data".

Maybe I can have a shop check the fuel pressure for me.
Right, basic diagnostics first , also what codes?

I also wonder if you have a dying/dead coil. Your symptoms would match that of a coil (they dont give codes) such as the stalling at higher RPMs/gears and eventually bad idle.

Have you replaced any of them lately?

I replaced the plug wires and the engine hesitation, accelaration, stumbling, and idling problems all dissapeared. I also ordered some new coils, so when they come in I'll replace them for good measure as well.

There is still the occasional shake on the highway, which I believe is caused by the torque converter slipping, but I can live with that for a while, it's summer and I ride my motorcycle whenever it's not raining anyway.

good deal on the simple fix :)

Keep an eye on your tranny fluid colour. If it starts to go orange/brown the torque converter is overheating due to slippage and destroying the fluid. The planetary gears will be soon to follow. I found out the hard way!