loosing vac at idle causing misfire. Idle only car drives fine until idle. I lose about 10iches of vac at idle from 22hg down to 10hg then it starts to misfire/run rough as soon as i loose vac. Could the only problem be at vac/boost/im leak or could anything else cause a lose of vac. When you do a boost leak test, after u pressurise the system should your boost gauge stay solid or will you still loose a little pressure bacause when i do a leak test my gauge looses all the pressure very fast. I found a couple leaks. One in the intercooler and sent it back to road race to have them fix it but im still losing all the psi and i can't seem to find anymore leaks. Could a lean fuel condition effect vac? Sugg please, Thanks

 

It sounds like you have a pretty good sized leak somewhere. Any air that is getting into the intake without going through the MAF is not read and therefore the computer will not add the proper amount of fuel for that amount of air. Check for all your leaks, plug em, and then reset the ECU. Hopefully that should solve your problem.

 

i did another boost leak test and found a huge leak in a couple connecting the intercooler piping. Helped but didn't fix the prob completley. Instead of losing 11inch of vac and barley wanting to idle now im only really losing about 2 inches of vac. At idle it's at about 18inch of vac, but when i let off the gas it drops to about 22 and back up to 18hg which i know it's suppossed to drop, just info. At idle it still misfires a little and smooths out and start to misfire again,but alot better then before. Although i still have to change the plugs because there prob pretty bad cause it was so lean at idle. Also on wastegate only i can only get about 4psi of boost. I have a MB but i have it turned down until I get it running 100%. Thanks for the help and any more suggesstions would be appreciated.