St-185 Idle Problems

[flyingtele]

I recently bought an ST-185 GT4, and it has and aftermarket dump valve and exhaust system. My only real problem is that when you start it it will idle roughly for about half a minute to a minute, and then just splutter and die if you dont give it any gas. Once driving the engine runs fine and has plenty of power and it boosts well. Where abouts should I look for the problem? I thought the pipe that bypasses the turbo and goes straight into the manifold could be dirty, or it might be dodgy spark plugs and leads, or it may be a timing issue.

Any help would be appreciated

[GTForbes]

check the vaccum line for the dump valve, and check the timing, two easy job. if possible take the dump valve out of the equation and block off the vaccum pipe

[flyingtele]

okay, how do i check the timing and what do i look for?