Car plagued with problems since rebuild. Help me with this new one...

[bpestilence]

Okay, to recap.

I fully rebuilt the engine in my TSi. New rotating assembly, new seals, bearings, pumps, pulleys, belts, etc. New exhaust manifold and turbo, new IC pipes, new exhaust. Now I am running a AEM F/IC-8, a AEM water/meth controller, an Innovate WBO2, and an AEM boost control solenoid. Virtually everything has changed in the car, so it shouldn't be hard to imagine why I am having a lot of problems with bugs.

At first after the rebuild I couldn't get the car to start. I replaced the transistor, the crank angle sensor, and checked the MAP and CAS to make sure they were working. Finally I figured out that a fuel injector was bad. That got her running. After that I just tuned the car.

Then, for the first test drive, I started to have problems with the car not acting right except for at idle. Basically the car idled fine but as soon as I gave it gas it would hesitate badly and sometimes die. I thought that I had fixed that with tuning, but it never really went away.

But I did get the car running pretty good, and took it for a drive around the block. It worked fine, but then when I got above 3000 RPM it just died. Then a new problem started. Now, if I start the car, it will run fine for a few seconds and then JUST DIE. Then I can start it again and again, but always with the same symptoms.

Here is the weird part. I unplugged the MAF sensor, hoping to put the car into Alpha-N mode and get it home. Worked. The car ran fine and I thought that I must have a bad MAF sensor.

But today, I went to test the car again with another MAF, and the old problem is back! Start it, it idles for a few seconds and dies. I tried unplugging the MAF again and it didn't work. Still refuses to run more than a few seconds.

Can anyone figure out what is going on here? I have a feeling that some sensor is going bad and causing this, but I have checked or replaced every sensor I can think of. I have read some threads blaming the crank sensor, but mine is brand new (and plugged in, and I checked again to make sure it had not come loose), and I have read a few threads saying to check the ECT sensor, which I have not replaced but which appears to be fine (and is also plugged in)

I am pulling my hair out here. The car was less of a hassle when it blew smoke and ran like crap.

 

[bpestilence]

As suggested by some in PM's, I did a boost leak test. I did find some pretty decent leaks in the couplers that I was able to fix by tightening them. After I got all the leaks, even the small ones, fixed, I tried again.

Still no dice. Next I am going to start tracing wires. I don't know what else to check. What could cause a car to run fine for 3 seconds and then just die without even sputtering? Every time?

 

[rock1t]

it's a dsm.

 

[bpestilence]

Update:

Okay, I replaced the IAC motor and now it seems to run fine. I am not going to call it resolved yet, though, until I get some driving time on it and verify that it is running right.

Right now I am having trouble tuning the F/IC. I keep having to change the injector trim to get it to idle at the correct AFR.

Edit Update:

After doing a lot more tuning, I have it running a lot better. Getting the BISS set just right was a pain in the butt. And with no FIAV the engine runs pretty rich until it warms up. But, it runs and it boosts and makes okay-ish AFR's at and off idle. The fuel economy is going to suck until I get it tuned better. Still trying to find an AWD load dyno on Oahu.

But I think I have fixed the problem. The IAC motor was perhaps just shutting after a few seconds? I suppose it is possible that if one of the windings was bad, it would slam shut when the stepper motor tried to go to that position.