My EGT reading is between 1500-1600 F when cruising on the highway at 75 mph. Is it normal or too high? Strangely, when i hit boost, the temperature drops down to 1400 F.

setup: Autometer EGT probe and gauge. The probe is tapped on the downpipe flange.

 

sounds like at cruise your ECU leans out your afr's to save on gas. seems perfectly normal.

 

I would say that your temps might be too high. The probe is after the turbo, so the manifold temps (what most people go by) are ATLEAST 100º hotter, possibly more, depending on the turbo and internal vs. external wastegate...

 

I think you need to richen it up just a bit, but if you are using a ECU that you can not run in open loop then you wont be able to change it at highway speeds

 

You could bump your static fuel pressure a couple pounds to compensate for it. I know a few of the newer cars are lean burn.. they have cruise af ration of 30:1 and greater. the computer only gives them enough gas to stay running. Your car might be set up this way. Its not bad.. The fact that when you hit the gas it drops is a good sign..

 

I'd say richen it up a bit. It sounds like you have the same thing I had a while back. I just didn't feel completely safe with the needle going straight to 1600 when I was cruising. How could I tell if it was too lean with it going straight to 1600. It would go back down to 1400 when I started boosting...similar to you. I have an autometer egt as well with a competition probe. It was a simple fix by richening up the fuel a bit between 3000 to 4000 for me.