I recently posted a thread about exchanging the upper intake inckuding, plenum, runners, and tb on my 88 iroc with a 350 tpi. Well initially the car would not start and just fire up and die. Well there was an popping noise very evident upon idol with the car so in thinking of the plenum gaskets and runner yesterday my dad and I removed them all and checked if the gaskets were in the right spots and they were so I put everything back together and retorqued the bolts. Well today the car started up and would go through all the rpms very smoothly, but when returning back to idol the car will still die. I unplugged the maf and start it up and the car will idol and run somewhat rough though. With the maf the car will not idol at all. Well I was just wondering this I recieved a high air flow code from the maf and the only change to the new plenum is I ported it and matched all the gaskets. I placed a new mat sensor too. It just seems that I am getting more air into the intake than the maf and tps are registering because of porting the plenum. The leak or popping I believe is coming from the mat sensor because I forgot to use a thread sealant on it. Should I just switch back to the old plenum thanks Tim

 

You DID reconnect the PCV/CCV lines in the correct places, right?

It really doesn't matter how big the ports and runners of the plenum mught be. At idle, the throttle is closed, and all air (other than leakage) is routed through the TB and IAC. The MAF should get the same air volume reading regardless of the plenum volume. If the MAF sensor was somehow damaged, not sealed when it was installed, or skewed so that airflow through it is altered and not passing through the sensing tube, the symptoms you describe might occur.

 

Thanks for the response to answer your question the ccv line/pvc lines are all correct along with all the egr and vaccum routing. I just reconnected them all after reassembling. It seem though there is a distinctive vaccum leak and I believe it is the mat sensor itself. Can this cause a leak of such proportions to affect the idle but not upon acceleration itself. What is this popping noise I am hearing?

 

The popping (backfire) is possibly due to lean mixture on a cylinder or two. That is consistent with avacuum leak. The MAT (on the underside of the plenum) needs to be sealed, along with any other openings in the plenum, like hose connectors and the gasketed joints.

 

Thanx vader tomorrow I am planning on switching out the plenum and resealing the mat and vaccum fittings Tim