I've been having a consistent problem with my '96 5.2. Within a minute of startup, warm or cold, the engine will stumble for about 30sec and then come back to normal for good. It happens EVERY time.
If I'm stopped, the engine will lug for a few seconds and then jump rpm's only to lug again. If I'm driving, I will lose power and the engine stumbles. Sometimes I can power through it but the power loss is still there for a short period of time.

My ignition is fine. I just replaced the IAC. I get an engine light sometimes but it doesn't stay on for more than a couple days. Right now, I have no codes.

Here is what I've found. When the rough idle/stumble occurs, the IAC pulls back and allows excessive air into the intake. There is a loud "sucking" sound through the IAC port. I'm guessing that the rough idle is being caused by an overly lean condition caused by the excess air but no extra fuel to compensate.

My question. I know that the ECM controls the IAC, but what sensors does the ECM use to determine the IAC setting? What would cause the IAC to pull back at the same time for the same duration every time I start my truck?