I might have missed this from an earlier post, but how is the engine at idle? Is it rough or "hunting" when you're at a stop? I had this similar problem and it was my MAF (if you disconnect yours, does the idle smooth out?). I ended up replacing the MAF (even after a good cleaning) and cleaned the ICV just to be sure.
By far, the very best thing you can do here is invest in an OBDII scanner that plugs into your laptop. Just because you don't have an MIL on doesn't mean that you don't have a "pending" code on the ECU. They sell for anywhere between $40 to 200 on eBay. Every DIY'er should have one!!!! Anything that uses the "ELM" chip will do.
Also, the OBDII scanning software will give you live readouts of ACTUAL sensor values so you can, at least, correlate any bogus numbers. This way, you don't blindly go and replace parts and "hope for the best".
Testing for vacuum leaks is best done via "smoke test" at your local mom and pop auto shop. They shouldn't charge you more than an hour's work of labor.
How many miles are on your car? If you're over 100k, then you *may* be due for new pre-cat o2 sensors, but for the most part, those are fairly solid (again the obdii sofware will give you very good indication of any declining health).
Keep us posted!