please tell me what is going on!

I have a 1991 5.0.i just had 24lb injectors,a 70mm throtle body,and a 75mm mass airflow sensor installed.it has a cobra intake the rest of the motor is stock.when you start the car it revs up to 1200 rpm and holds their then it drops to like 950 and hunts to 1000.when you give the car gas the rpm stays high.the tps sensor was replaced and adjusted the iac sensor is new the map sensor is new.please someone tell me what is going on because this the car ran great for 4 years no problems

Sounds like an issue I had with mine not long ago. Do you have cats or off-road pipe? Makes a difference in idle quality depending on cam, intake, throttle size, MAF size etc. I've got GT40 intake, 73mm MAF, 19lb injectors, cone filter with shroud and home made bumper scoop, 65mm TB, stock cam. Before OR pipe, it would hunt and drift with idle. After OR pipe, smooth as silk. Also, I could clutch it going down the road at 60-65, and check engine light would come on before OR pipe, not after. Backpressure and free flowing exhaust affect it. Headers would also affect it. My heads and headers are stock.

i have bbk equal length headers, off-road H pipe, and flow master 40 series mufflers. No engine light has come on, I didn't start having these problems until doing engine upgrade.Swapped computer and still having same problem.Thanks for the info.

Just to make sure, is the MAF calibrated for the 24 lb injectors?
Did you reuse the sensor? Are the elements clean? I've heard people with wandering idles that have cleaned the elements and that fixed their problem.

I can't say for definite since I've never had that problem, just passing on ideas... Either way it's not a bad idea to clean them. Just be careful...
[addsig]

The 75mm MAF may be the issue. If you can switch to a 73, that might bring the computer back into the adjustment table. Either that or switch back to 19lb injectors. The stock injectors can handle over 300 HP. The Cobra intake is good for 245 on a stock motor.