Hanging Idle w/new upper intake plenum installed

eggmass · Nov 25, 2008

I recently installed a Granatelli Motorsports "Shark" Upper Intake Plenum, and now my idle hangs at around 2100 RPM. I replace the PCV hose, as well as a new gasket for the IAC. Does anyone have any other hints as to why the RPMs rev to 2100 by itself?? It is definitely a vacuum leak, I just can't trace it down. Any help would be appreicated.
By the way, it is a '98 GT 4.6L 2V with K&N Cold air intake.

Thanks
eggmass

Sxynerd · Nov 25, 2008

eggmass said:
I recently installed a Granatelli Motorsports "Shark" Upper Intake Plenum, and now my idle hangs at around 2100 RPM. I replace the PCV hose, as well as a new gasket for the IAC. Does anyone have any other hints as to why the RPMs rev to 2100 by itself?? It is definitely a vacuum leak, I just can't trace it down. Any help would be appreicated.
By the way, it is a '98 GT 4.6L 2V with K&N Cold air intake.

Thanks
eggmass

Did you replace the T/B also? I'm sure it is your Decay Rate, adding any amount of extra efficiency has the potential to screw with your Decay rate. Two ways to fix it...

Temp but effective is the IAC mod.

Preferred way is to have your Decay rate adjusted within the tune. Any new Hand held should be able to adjust it.

squeak93 · Nov 25, 2008

You mentioned vac leak.... Have u sprayed around all the gaskets you replaced with throttle cleaner and listened for engine surges? You could of sucked a gasket in or tore one during install.

eggmass · Nov 25, 2008

squeak93 said:
You mentioned vac leak.... Have u sprayed around all the gaskets you replaced with throttle cleaner and listened for engine surges? You could of sucked a gasket in or tore one during install.

Yes, I did spray it and the PCV hose going into the plenum caused a drop in RPM, but I have since replaced the PCV hose as well as the IAC gasket. I imagine that it could be the throttle body gasket because I did not change that.

Jbauer · Nov 25, 2008

eggmass said:
I recently installed a Granatelli Motorsports

Theres your problem right there

Jbauer · Nov 25, 2008

i've never had a problem with the decay rate. the granetelli piece doesnt flow very well so it couldnt of been a very big diffrence even with the stock throttle body. I have an Accufab throttle body which outflows pretty much everything and even I didn't have any problems running it with the stock throttle body for a long time.

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