Intermittent Idle trouble

Have already looked at related post and haven't seen anything that is quite like what I have so here is the new thread. Every now and again (only 3x so far) my car will fall off of its idle. It has only done it when the car was at operating temp, but not all the time at operating temp. The car will run just fine and then all of a sudden it will drop below 500 RPM and act like it is missing. I have seen that it can be anything from bad engine mounts to a fuel pump, so here are the specifics on my car. It's an '89 AOD with 91010 miles. Bought the car about 8k ago. Within that time, I have resealed the upper 1/2 of engine (minus HGs), put a '95 SC on it, 1.73 Roller Rockers as well as a mild tune-up (wires, plugs, belts) I haven't touched the fuel system yet at all. It appears that my engine mounts are worn, but not gone yet. In gear with throttle the engine moves 1/2" to 1" at most. Just before it falls off its idle, I have not noticed any other symptoms that would help pinpoint. It is a sudden occurance and lasts until the car cools back down (i.e. next morning drive to work). Temp gauge does not get above 12:30. The check engine lite does not come on (until after the car dies, happened today). All fluid levels have shecked out ok. I'm suspecting it could be a TPS or the ?idle air control? sensors. I don't have a scanner to pull the codes as of now, if there are even any. I'm also not willing to pay $65 for the shop to pull the codes either. Just hoping for a little more direction before I start throwing parts at it. If anyone has had similar problems, please let me know. This is my daiily driver for now.

Do any of the accessories "kick-on" just prior to the drop in RPM's? Like maybe the electric cooling fan for the radiator? It could be some sort of drag on the electrical system causing the problem or a mechanical load. I have noticed that when my A/C compressor would kick-on (last summer) the RPM's would dip for a moment until the IAC could catch up. I would suspect that you may have an IAC that is starting to fail, but it could also be engine mounts if you can see an inch of block movement. It is really a challenge to isolate these types of problems without doing some serious diagnostic testing. Just try checking the simple (inexpensive) things first.......

No accessories turn on just before. Not even the fan. It cause the CE light to come on today, so I'm going to get the code and maybe that will direct me closer. Thanks though. I'm thinking still it's an IAC or TPS. Symptoms so far indicate as such. If it were engine mounts, I think that I'd be getting symptom on a more regular occurance. (Not that I'm not going to change them, just want to make it to spring!) Thanks again.

For anyone who has looked at this post, it was the O2 sensor. Got the codes pulled today. Just FYI.