Recently I replaced my head gaskets and had a valve job done to my 2000 Mustang with 3.8L. The only modification is a cold air intake that I will come back to. Now that it is back together it cranks over for a while then starts real hard. Once started it runs amazing for a few minutes or until idled up. At that point it begins trying to suck a bunch of air, making a loud low-toned whistle sound then dies. It will keep doing this repeatedly.

The only thing I reinstalled differently was the intake tubing. I had to buy a new air filter and cut a little off of tubing so it would fit. I did not mess with the MAF sensor other than spray it with cleaner.

Does anyone have any ideas where I can start?

 

Sounds like you have a leaking head gasket or lower intake to head gasket.

 

Sounds like a vacuum leak. Check all of your hoses, make sure they're on and sealed. If those are good then you're sucking in air somehwere on the intake. A simple, dangerous, but effective test is to spray starter fluid at the suspected area of the leak. If they idel jumps, thats the spot that's leaking.

 

Thank you for the replies. I tried the spry test for a vacuum leak and didnt have any change in idle. I was able to run it long enough that the enigine light lit up and it spit the P0122 Code for TPS. I tested it per the book and the voltage doesnt seem to be changing when the throttle moves. I am going to try to replace that and I will report back.

 

Ok. I changes the Throttle Position Sensor and that removed the engine light, but the car is still running with a slight vibration and will die when reved to 3,000 RPM. The exhaust also smells a bit rich. I have been checking the oil and coolant and it does not appear that they are mixing together as I would expect with a bad head gasket.

Any other ideas?

 

Head gasket could be blown between the cylinders which won't mix the fluids.

Another home school test is to unplug the AIT (air intake temperature) sensor. Get a small hose and put it into the hole and try to seal it best you can. Take a cigarette or cigar (DO NOT INHALE) puff on it and blow the smoke into the air intake. If you have a vacuum leak you may be able to see the smoke come out of the motor. You will need to get a big mouthful of smoke. A little puff wont do it. This is an old school method that is a safe effective way to find the smallest of leaks and it doesn't damage the motor.

If it's the head gasket you will need to run a compression test. However keep in mind, there are instances in which a head gasket is blown in such a way a compression check will not catch it. I had this happen once with my old 5.0, and I've seen it happen multiple times on here. It's not common but does happen.