1988 mustang gt running rich with idle issues?

Hi, first of all just want to let you know its not a vaccuum leak. Freshly built 347. It idles eractic on cold start but then evens out and the cam lopes normally. Idle hangs for a minute if I hit the gas. Throttle cable is not hanging up either. After it reaches operating temperature the idle raises about 2 to 300 rpm? It also is running rich. I cleaned maf and the idle bypass. Thermostat is a 180 degree. I just don't know what else to look at.

It sounds like an oxygen sensor. Easiest way to check it out is to diagnose it with a hand held code scanner. You can find them on eBay for about 20 bucks. It's called an actron code scanner model number CP9015. They are made for older domestic Ford's, Lincoln's, and Mercury's. I've owned several 5.0's over the last 30 years and those scanners work great.

The car came with a speed density air volume sensor, which was replaced for 1989 by the mass air sensor system, which is still in use today. One of the problems with the speed density system was the idle - It was next to impossible to get it smooth. One of the things that contributed to the idle problems was the engine fan would blow air across the mouth of the intake, & that was enough to unsettle the idle. The problem was bad enough that back in the day you could buy a kit & convert your '88 to the newer mass air system. So, IF it still has the speed density system, suggest you upgrade to the '89 mass air set-up. Doesn't involve any deep electronic knowledge, just swapping parts.