Odd question, but I removed my engine cover recently and started the car. Well there was a pronounced hissing from one of the bolt holes in the intake manifold. This of course is causing a vacuum leak and the idle to jump around a bit. I'm guessing at some point someone used too long a bolt and punctured the manifold? This isn't somehow a design 'feature' right?

Once the cover is on and I have a bolt in, it appears to seal it and the car runs totally fine. Any issue with simply leaving it as is? On the plus side I suppose I can now run seafoam or other cleaners through there if i needed to clean the valves etc..

 

Take a picture with your finger on the bolt that's hissing. The OEM engine cover bolt locations cannot hiss because they're on casting protrusions that are outside of any airspace.

 

It may be normal, the one below it does not take any bolt as the engine cover is only secured by one bolt in the center.

 

Ahhh I missed the part about it being an HR motor. I'm not too familliar with that upper plenum but just from looking at it it's definitely possible someone ran a longer bolt through and broke out the bottom of the casting. You would feel suction with your finger, if so then just add a rubber washer under the bolt or use a very light coat of teflon plumbing paste (don't recommend teflon tape) to seal the threads of that fastener.

 

Thanks, i do have a rubber washer but can add some extra sealant on the threads although i dont think it leaks as is.

 

Had same thing happen here. Didnt hear the hiss at first. I even did a throttle relearn. 1100 rpm is high compared to the factory 650 rpm. Im replacing valve covers before winter so I will see later whats under intake.