Lower intake cracked?
 

‘02 XLT 4.6l with 160k.
had rough idle, replaced plugs, injectors, coils. Throwing different codes, latest was P0175. Mechanic did smoke test, says lower intake manifold is cracked. He says it’s plastic, I know for a fact the upper intake is aluminum. I’ve seen aftermarket lower intakes for up to year 2000 and those are metal. I can’t find a lower intake for this year truck anywhere online. It’s Sunday so dealers are closed. Any ever dealt with this?

The manifold might well be cracked but a vacuum leak should give you P0171 and/or P0174. P0175 is a "rich" code, not a vacuum leak/lean code. The code doesn't match what the mechanic found. You'd have to question the mechanic's ability to find a crack in a manifold also, if he didn't know that. Might be working on the wrong solution.

People are going to want to know if you had a code when you had the rough idle. Did the code only appear after you installed the new parts? Did the idle smooth out with the new parts or is it still rough? And, what brand of parts did you use?

Several months ago, it had a P0302 code. Replace coil on #2, all was well. Then about 6 weeks ago, it started running rough again. Figured it was a coil, so replaced all 8 coil packs, and injectors. Had misfires on #3 & #7. Replaced all 8 plugs, reseated coils and injectors. Still ran rough, but misfire codes went away. Motorcraft platinum plugs. Coils n injectors came from Amazon n eBay, they were some no-name brands. The P0175 code is intermittent. Frustrating. I asked him today if this could just be intake gaskets. He said it could be. He did a smoke test and sent me video. I don’t know enough about a smoke test to disagree with it, he did say he could repair that plastic lower intake plenum so that’s a plus, I guess.

Should have used Denso or Motorcraft coils. Those no name knockoff coils can be junk right out of the box.

My first Ford. Probably last unless I go really old school. Live n learn. I’m hoping this is just an intake gasket leak.

In my *VAST* experience working on these trucks, I've only seen one lower intake problem and, like BarebonesXL said in post #2, it will not set that DTC you have provided.

I’m hoping he will have good news when he takes it apart. And by good news, I mean a gasket issue or something else ‘minor’.

Well, I look forward to others commenting on my following statement. I have not seen an aluminum intake manifold on a 4.6, they are all (original) plastic and they can and do crack occasionally. Maybe its unrelated to your code but it may still be an issue.

The 4.6 2v in the truck didn't get a plastic intake 'till '07 or '08. Is that what you were looking forward to?

As I recall, the 99 is the only year that came with the aluminum intake with PI heads. It's possible it was swapped. BUT, I do agree with you, it should have been plastic from the factory.

Am I remembering this accurately @Jbrew @akdoggie ?

EDIT: Maybe that's only the 5.4 though.... now that I am thinking a little harder, maybe the 4.6 didn't get PI heads until mid 2000 or 2001?