Bad idle, low vacumm

[JeanDSM]

My car idles at 550~650rpm and the vacum is at 5mmhg and makes funny noises like a pop corn machine inside the intake manifold and like a a loose accesorie belt inside the intake pipe ( what first came into mind to describe it ) sometimes revs nice sometimes at wot stays at idle, the car currently hass 880cc inj and maft translator with stock ecu.

I move the biss srew and nothing happens what could it be?

 

[ypnas777]

boost leak? I don't know much about the maft translator but is it dialed in correctly? Is there a feature that dials in those injectors you have because you can't just drop in bigger injectors without a way to compensate 4 them.

 

[JeanDSM]

yes they are dieled in and there are minor boost leaks

 

[ypnas777]

check timing, compression

 

[86Irocz]

A boost/vacuum leak can cause both of those problems. Since you already know about your leaks, why not fix them to eliminate the problem?

 

[JeanDSM]

ok i will try to eliminate all boost leaks, its something nearly impossible on DSM's jaja
but i will,
the funy noise was disturbing me

 

[bling5tatus]

something jumping around in your intake manifold? Maybe a fubar'd valve? Or a rocker popped itself loose. I'd take the valve cover off and check that out as well.

 

[Talesin]

Remember to keep your throttle open when you boost leak test, and make sure the valves aren't overlapping so you won't lose all the pressure out the exhaust. A vacuum leak happens post-TB. Possibly a messed up TB gasket or mani->head gasket, or the mani nuts might not be torqued down properly. Boost leak with the TB plate open will tell you where it is.

Low vac can also be caused if your timing belt jumped a tooth, line it up and use a straightedge through the middle of the cam gear bolts to make sure the marks are actually lined up, it can be hard to tell without a straightedge there as a reference, especially with only a one tooth jump.

I'm surprised that it's idling all right with 880s and just a MAF-T.. usually the deadtime on the injectors will cause really crappy running at idle. Also make sure that the honeycomb in your GM MAS isn't coming off. If one edge is broken and flapping around or something, that would cause problems too.