I have been out trying to diagnos a irregular boost pattern on my FD and I purchased a KD Tools brand boost and vacuum gauge. At idle the needle gives me a perfect reading (nice and steady).

When I perform the boost test at WOT in 3rd gear, the needle really bounces around. I cannot seem to get an accurate reading as it bounces furiously from 7 - 11 at 3000 rpm and the same at 4500 rpm.

Is this normal? Or is something else causing this?

I had the same reading before I replaced all the vacuum lines.

 

for a stock engine and turbo that is not normal. try another gauge.

 

Thanks.

 

Most boost gauges use a restrictor pill (either inbuilt or inserted into the line) to smooth out boost pulses.

 

Also depends on where you take the signal----the most unstable place are the blanked nipples on the UIM.

 

I just experienced the same problem after installing my boost guage (first mod!!!) the needle bounced around like crazy once I got on the throttle, the solution was as moconnor said I forgot to install the small bass restrictor pill due to the stupid japanese instructions once I spliced that into the line the guage read perfectly.

 

I had the same issue. I put a resistor pill in and mine was mounted on the steering colum plastic which was vibrating. First try holding the guage to make sure its not just picking up vibrations. If it still shakes try the restrictor pill.