Nissan Repair: Nissan 200SX S14 tick over and engine rattle, fuel management unit, nissan 200sx

Question
Model: Nissan 200SX S14 1996 (P) 2Litre Turbo.

2 problems:

1) When engine is hot, the car tends not to idle very well, often having a tendency to chug at 400rpm or die completely e.g. at traffic lights / junctions (but not always). This doesn't happen before the engine heats through. Any ideas? I have had the car regularly serviced but this doesn't make any difference and the mechanics don't seem to know what the problem is. Engine management system was their best guess.

2) I have recently fitted a boost valve and increased the turbo boost pressure to 14PSI but there is a quiet rattle on the engine on hard acceleration. (This mod didnt affect the tick over problem either). Is this the turbo complaining at the extra work or something else? I'm going to take the valve off until I know whats wrong (if anything) but I'd appreciate any advice.

Answer
Dominic,

The idle air needs to be increased to get rid of the low idle.  The reason that it idles fine when cold is it is in cold start mode and it is getting extra gas and air to keep it running while it is cold.

If you are getting a tick while you are under boost you might be pinging and that is not good as it will destroy the rod bearings over time.  If your boost is increased too much it will ping and that is why some systems have increased injector capacity or a fuel management unit that increases fuel pressure under high boost conditions.  It is imperative that the tick be eliminated or you are going to blow the engine.  So, either a fuel management unit or larger injectors need to be added for the increased boost.