low idle and no power

My 94 suburban has a very low idle especially if I have the AC on. I live in AZ so it is always on. I have had it into the shop twice and all they tell me is that my timing advance is not constant. They said it is either the computer of the timing chain. I have replaced the computer and prom and that didn't help. It is a new professionally built engine with less than 3000 miles so I find it hard to believe that it is the chain. Before I tear into it does anyone have any other suggestions. I have also replaced the distributor, ingnition coil, ignition module, and all of the sensors and solenoids that I could find at the time that the motor was replaced. All except the O2 sensor. I am not getting any trouble codes so not sure what else it could be besides the chain.

I really don't want to tear this thing down again:banghead: Any help or suggestions would be greatly appreciated.

My 94 suburban has a very low idle especially if I have the AC on. I live in AZ so it is always on. I have had it into the shop twice and all they tell me is that my timing advance is not constant. They said it is either the computer of the timing chain. I have replaced the computer and prom and that didn't help. It is a new professionally built engine with less than 3000 miles so I find it hard to believe that it is the chain. Before I tear into it does anyone have any other suggestions. I have also replaced the distributor, ingnition coil, ignition module, and all of the sensors and solenoids that I could find at the time that the motor was replaced. All except the O2 sensor. I am not getting any trouble codes so not sure what else it could be besides the chain.

I really don't want to tear this thing down again:banghead: Any help or suggestions would be greatly appreciated.
Has anybody checked the operation of the idle air control?

I am not sure if anyone has checked it, but it was one of the items replaced when the motor was done. How would I go about checking it? Is this something I can do myself? I have to tell you that the dealership service department has enough of my $$$ at this point...especially since the problem still exists.

The counts commanded by the pcm and responded to by the iac , can be checked on a high line scanner, get this back to the shop and insist they correct this.

I will. Thank you. Your advice is greatly appreciated. I'm sure that before I finally bring myself to part with this beast I will require more.

Do you know if this is an IAC problem would that also cause the truck to surge while accelerating and sometimes load up? I also got an error code today indicating a lean exhaust mix. Would be nice if all these issues had the same source but with my luck I might be asking too much.

Don't think so. The IAC is only used during Idle, as soon as the throttle body opens up the butterflies on the IAC close. But your EGR can cause a low Idle if stuck open and it would have a load on the engine. Also if your EGR is stuck open you can also get a lean mixture. But your O2 should work in conjunction w/ your fuel system to compensate for the excess air.

Thanks guys. This gives me a few areas to start diagnosing. I'm taking it into a different shop tomorrow to check the IAC. Maybe they will catch something else. You guys are awesome and I appreciate all the help.