04 GT New intake manifold and car now has a rough idle

Jimmy2Valve

Member
Sep 24, 2019
5
1
13
21
California
I'm new here but I have a 04 GT standard trans and my OEM plastic manifold broke at the heater hose fitting so I replaced it with a professional products typhoon intake manifold and I installed it and now the cars idle is very rough. Bouncing between 1200 rpms and 500 rpms. Thought it could be because I may have air in the cooling system but I'm pretty sure I got all the air out and now the car runs fine sitting but as soon as I rev it or let off the gas and coast with the clutch down its sits at 1200 rpms then almost dies and goes to 500rpms then its back to normal idle at 800 rpms. All my vacuums lines are good and I'm running out of ideas, I replaced my plugs about 300 miles ago so Idk if it's a spark issue. Could it be a bad IAC or TPS since i did clean the plenum with brake clean and parts cleaner while it was off
 
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Sluggie24

Active Member
Apr 8, 2017
135
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Try spraying brake clean around the intake manifold with the engine running and see if the idle changes. It's possible there is a vacuum leak somewhere.
 

Shuttleman83

Active Member
Jun 30, 2019
102
9
28
USA
Clear it, tighten it back up, turn car on and let it idle two minutes with no accessories or revving, then turn off, turn on and let it run for two minutes with all accessories. Should do you good unless you have a bad vac line, disconncted vac line, or accidentally forgot something.
 

Jimmy2Valve

Member
Sep 24, 2019
5
1
13
21
California
Well I finally found my problem, my IAC valve must have clogged because I removed it and used almost a whole can of throttle body cleaner in the IAC then bolted it back on and now the rough idle is gone and I got my power back. I missed my stang so much
 
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