leaking throttle body, lean code
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Mountain Pass
Joined: Jul 2019
Posts: 141
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leaking throttle body, lean code
How common is a leaking lower gasket on the intake manifold assembly? I sprayed the left side (ds) and it changes the idle, so i think that's were the leak is. Will need to smoke test it to make sure. Truck runs great, but plugs on drivers side have a lot of carbon.
2001, 4.2, 230,000 miles f150xlt
2001, 4.2, 230,000 miles f150xlt
Last edited by Michael Lizotte; Jan 14, 2026 at 01:00 PM.
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Mountain Pass
Joined: Jul 2019
Posts: 141
Likes: 2
Drivers Side. Parts show a lower and upper gasket set. Would you recommend replacing the intake with a after market one too?
Fleet Mechanic
Joined: Jun 2023
Posts: 1,373
Likes: 382
From: WA
I think that you're talking about the intake manifold assembly. 2001 has the plastic upper and middle manifold, which work just fine, not like the early 4.2 manifolds. The most common leak cause is the isolator bolt grommets hardening. The isolator grommets are what press down on the manifold, causing the gaskets to seal.
Anyway, the fix is to replace the grommets, or just replace the bolts which already have the grommets attached. While you have it apart might as well replace the upper gaskets, and check the IMRC bushings. Unlikely that you need to mess with the lower manifold. Watch out for torque specs, some are in inch-pounds.
https://www.rockauto.com/en/catalog/...tor+bolt,14336
Here's a few videos.
isolator bolt videos
https://www.youtube.com/results?sear...isolator+bolts
Anyway, the fix is to replace the grommets, or just replace the bolts which already have the grommets attached. While you have it apart might as well replace the upper gaskets, and check the IMRC bushings. Unlikely that you need to mess with the lower manifold. Watch out for torque specs, some are in inch-pounds.
https://www.rockauto.com/en/catalog/...tor+bolt,14336
Here's a few videos.
isolator bolt videos
https://www.youtube.com/results?sear...isolator+bolts
Last edited by BareBonesXL; Jan 14, 2026 at 12:14 PM.
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