Stevolwevol

I replace IAC, TPS, temp sensor. It started with a mild stumble, now it runs rough at start up, loss of power, and generally running very rough. I don't trust driving it since it continues to get worse.

Injuneer

Have you scanned it for codes? Have you checked the fuel pressure? Have you checked the spark plugs and plug wires? How old is the O2 sensor?

What year is the car?

Stevolwevol

Plug wires are fine, replaced the plugs, cap, and rotor. They were pretty far gone. It runs better w/tune, but I still get intermittent stumble at low RPM's, between 1 and 2000. I didn't get any codes, mechanic didn't either. Fuel pump seems ok, pressure was fine.

Injuneer

What about the O2 sensor? Did you check the fuel pressure out on the road, with engine under load, or only at idle? Any signs of running rich or lean due to a leaking/plugged injector? Don't know if the EST module in the distributor can be tested, but that can be a source of rough operation/stumble. Is the any indication of spark knock (detonation) due to a lean condition or running hot? Knock retard can be perceived as roughness.

Does your mechanic have the ability to pull up the long term fuel trims (BLM's) that would indicate if the ECM is having to make huge fuel corrections, in response to a rich or lean condition?

Stevolwevol

It was a bad EGR valve. I disconnected the vacuum line, and plugged it. It ran fine. I was going to leave it this way, but I picked an EGR for $20 because the box it came in was damaged (normally $42). Works fine now.