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Discussion Starter · #1 ·
Hello,

I have a 1994 GMC Sierra with the 5.7 TBI and recently it has begun running really rough at startup, but smooths out to normal after 30 seconds or so. It does this regardless of the outside temperature, from 90 degrees down to 60 degrees, it does the same thing. It also occasionally backfires through the intake once or twice but it doesn't do that every time.

New plugs, wires, rotor, distributor cap, coolant sensors, still doing it.

I recently connected to the OBD1 and used TTS Datamaster to pull data when it's running rough.

I have these readings when running ROUGH:

RPM - 775
Coolant - 67°F
IAC - 150
Spark Advance - 33°
MAP - 48

I have these readings when running SMOOTH:

RPM - 825
Coolant - 95°F
IAC - 51
Spark Advance - 20°
MAP - 28

Can anyone tell me if these readings indicate anything? Is there more data that you'd need to help me diagnose it? It's OBD1 so there's not nearly as much data as on OBD2 vehicles, but there are a few other readings I can supply if you need them.

Thanks for any help!
 
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