My mom and dad have a 89 cadillac sedan deville it is a v8 front wheel drive.Sometimes it starts missing and jerking like crazy and when you put it in neutral or park and take your foot of the brake it stops.When you going down the road at 50-60 it does it sometimes not always.The other day we were on interstate and it just starting missing and almost come to a stop on the interstae the all the sudden it acted like the transmission caught and it took off all the sudden.What I cant understand though is it dont do it all the time and it has been doing it off and on for 6 months now weve replaced everything to do with the ignition.It acts like its has somthing to do with the tranny,but if your parked and holding the brake it will do it till you put it in park or neutral and release the brake.Any advise would be helpfull.I know get rid of it and buy a new one.But they cant afford to right now and they have no other choice but to fix the caddy. :confused:

Not throwing a code??
If it has the digital dash try this. Push the off and heat buttons(simultaneously) on the a/c control panel for about 10 sec. This should bring up the diagnoistic controls for the ECM, BCM play around with it and see if you can find anything.
High blower is yes and low blower is no.
pushing no repetetively will back you up to previous pages. If I remember right.
Which engine is in it?
Single coil or multiple coil pacs? Injected or TBI? Replaced the fuel filter lately? how about o2 sensor?