I have just polished my plenum and runners..I put it all back together and it studders at 400-500 rpm then dies ...I have ripped it off and put it back on about 4 times now I cannot find any vacuum lines leaking....I did not replace the runner gaskets but that's what I am doing next...any other things that could be causing these problems? Never had problems b4 until I took runners and plenum off..Also I can hear air coming out somewhere on drivers side by lower runner so I hope new gaskets will fix it

 

Make sure to get the PCV system all hooked up. And double check the ducting from the MAF to the throttle body. Hopefully the runner gaskets will fix it though.

 

Crack the throttle blades untill you get a steady Idle as low as you can (600rpms?) then spray a water bottle around every last area of the intake, vacuum hoses, etc... When/if the engine stumbles you've found your leak. If you dont find one then its something else.