IAC questions

**Manimal** · 08-21-2017

I have a 94 GMC Suburban 2500 7.4l....I think my IAC is failing. I have cleaned it and the bore, set idle by disabling the IAC. But when I start the truck, it will stumble then recover and stumble again, then recover. does this a couple of times. Once its warm, and I shift into gear, it will stumble then idle will go up and down between 200-1000rpm until I give it gas and go. Coming to a stop it will do the same thing. I looked up a new IAC motor and 2 are listed...a 10mm pintle and a 12mm pintle. The one that's in the TBI now has been replaced before...my question is.... HOW DO I KNOW I HAVE THE CORRECT ONE?..
sorry, wasn't yelling, just wanted my question to stand out.
Thank you for any advice.

**myburb** · 08-21-2017

I don't know exactly where gm measures them so I only go by bigger and smaller. My 94 7.4 has bigger, my 93 7.4 has bigger and a tbi off a 92 I have is bigger. The outer edge of bigger is over 1/2 and smaller is under 1/2. Also info would be did it just start doing this with no changes or did you make some bin changes. Do you have data logging setup?

**Manimal** · 08-22-2017

Thank you. I just bought this thing and am trying to get it ironed out.

**Six_Shooter** · 08-22-2017

Have you observed IAC steps when this happens?

I doubt that the IAC is your issue.

When's the last time a full tune up was done? What is the timing at? What is the fuel pressure? etc...

**Manimal** · 08-22-2017

I just did a full tune up. cap, rotor, wires, plugs, timing set at 4*. Just got a new fuel pump in May. I need to get the adapter to check fuel pressure. When I took the IAC out, the pintle moved in and out like a PCV valve. Ive been told its bad.

**myburb** · 08-22-2017

You still didn't mention if this problem has always been there or if say it started after you did the tune up. When you go to check fuel pressure the 94 should be 28-30. The 7.4 has a different fuel pump than a 5.7.