Ok, ive been having this problem for a while now and iam baffled by it.
After the car has been running for a while and is completely warmed up it will start to surge at idle and in gear will stall itself and out of gear surge up to 1300 rpms and back down. Allso once the car is warmed up it wont pull the way it should from a dead stop, best way to describe it is it will stutter then go and when it goes it acts like its got no torque till about 1800-2000 rpm. I replaced the iac hoping that would help the surging idle but no effect. there are no codes and i just recently changed the plugs and wires trying to fix this problem. I get an occasional egr code but i acredit this to haveing no cat and a very free flowing exhaust system. I have been thinking that maybe the opti might be going bad cause the problem at full throttle in high rpms has it bucking a little right around 5200rpm. Any ideas on this problem would greatly be appreciated.

 

So far my biggest suspect is the optispark, since it hasnt been changed in 80k miles. im gonna try that and see where it takes me and hopefully that takes care of my problem.

 

Think about what changes when the engine warms up..... goes into closed loop, bringing the O2 sensors into play. May be related to that. Componenents start to heat up. IC Module and Opti optical module are two devices that are sensitive to temperature. Maybe even the coil. I'd check all the ignition system components before deciding if its the Opti.

 

new coil, new icm, and new plugs and wires. With my scanner hooked up voltages on the o2s read good, no slow readings. Same with iac and map sensor. runs the same with maf plugged in or unplugged.

 

I dunno,but I'm an idiot(furniture salesman),but it sounds like a vacuum leak,(intake manifold,or hoses associated with it).