2003 4.6 xlt

Hello. I bought this site unseen with 87k on it. It was only running with foot on gas. If I let it idle it dies when it hits 400rpm which happens immediately. I started off by replacing IAC controller. That did nothing. Then I tried cleaning MAF sensor, nothing. Then I drove it by a mechanic and he pulled the plug on the maf sensor. When he did that it idled without dying. He said I should start by replacing that. I did. And it still dies immediately. Any ideas? Thx. He said I should just change all the coils and plugs and it should be fine. He said the engine sounds and smells great when it has some gas. He doesn't think it's anything serious. He didn't seem to want the job. Told me to do it myself. I guess I'm thinking it's something more. Vacuum leak? Fuel pumps? Injectors? Idk. I'm trying to get this done cheap. lol

It might be something more, but you'll need to do the troubleshooting to find out. As noted in this thread:

Hello. Did I maybe just figure out a piece of the puzzle. I started researching about how to do a Smoke Test. I saw a vid where it said to go in by the brake booster. I never knew a car had such a thing. lol. Anyways. The other big problem with my car is the brakes are super duper spongy soft to the point of not braking right. Like when I push the pedal it makes a noise like air escaping. Then I read brake booster is a vacuum. Could my leak be there.m? Thanks.