Boost Gauge Casuing Idle Hunt?

[ARTZ]

Ok just a bit curious here...had an idle hunting problem for ages now, ever since I got car tuned actually....Trent offered to fix it for me thinking it was a tune issues but I never got around to it...

Now by accident I blocked of my aftermarket (garrett) boost gauge line...and magic...Idle problem has dissapeared...

there is a t-piece of the manifold so original dash gauge was working as well...the hunting would normally appear on decel..and was bad to the point is was trying to surge me into corners...then on pulling the car up it would bounce from 2000-500rpm then usually eventually settle..after anything from 10sec to 2 minutes....

Now it is settling to about 1200rpm on pullup then settles to just under 1000rpm somewhere....does this seem more like normal behaviour?

I cant find any leaks or anything in the line and I am quite happy to ditch the shitty gauge anyway..

but does anyone know why it would cause this?

[ARTZ]

just thinking, maybe because running MAP...gauge is acting like small leak and its losing manifold pressre..had no issues when it was AFM

[MBS206]

Leak in gauge itself?

[89CAL]

Yeah but MAP sensor will still read manifold pressure. If there is a drop in manifold pressure, the map sensor will react to it. Or should do anyway.

You could chuck a wideband on to see if there is a change in AFR when it happens though. I highly doubt it would be dropping MAP to a point where it would cause an issue but stranger things have happened.

[scotty nm35]

Did you disconnect any other hoses? Perhaps one has a split in it?

Is the map sensor on one of those hoses, or separate?

[89CAL]

Actually this is a good point. If the map sensor is on the same line as the boost gauge it may cause an issue

[ARTZ]

I didn't disconnect anything or touched anything else in the engine bay for that matter and they are on completely different lines...MAP is connected to fuel reg vacumn, boost is off the back of manifold.....its definitely this gauge thats caused it....when i put my boost gauge back in a few weeks back I accidentally plugged the line onto the bolt instead of the nipple (must of been dark)...effectively plugging it up...just noticed my boost gauge wasn't working yesterday and put 2 and 2 together...but why is it affecting it now I have MAp and not when I had Afm? I wonder if because the stock boost gauge is hooked up and still reading, its digital not mechanical yeah...i will try disconnecting it and see what happens..

and yeah there was a change in AFR..its just like it was hunting for an idle , cause eventually it would settle to idle...but in the meantime it was rich/lean/rich/lean