So this problem seems to plague a lot of 2004 - 2007 Vulcan engines. There are a lot of places where a vac leak can occur but this one seems to stump people. The symptoms usually include hard starting when cold, surging/erratic idle and hesitation on acceleration. My car was exhibiting the first two and was probably on its way to the third. After spraying starter fluid and checking all vacuum hoses I couldn't find any leaks. Then, while searching online, I found a topic on the other site that explained this problem and I decided why not put up a howto here?
Before starting it's always good to make sure you have the correct engine (only 2004 - 2007 engines have this part). The engine should look like this:
You will need the following tools and supplies:
1/4" drive ratchet,
6mm (7/32") socket,
T30 torx bit,
flat head (standard) screwdriver,
a new gasket (OEM part # 87072 S91 or the gasket from an oil filter will work [Bosche 3312 filter or similar - i used one from a Motorcraft FL-400s]).
Socket extension(s) at least 3" long.
The part in question is this thing here (red arrow):
Apparently this part goes by a couple names - the Intake Manifold Runner Control (IMRC) and the Intake Manifold Tuning Valve (IMTV). I will be using the former as it seems to be more descriptive of its function.
To start, first remove the top piece of engine cowling on the passenger side by removing the clips - be careful! Use the screwdriver to help pry them off (yellow arrows in pic above - 1 clip is out of frame). Also be careful of the vacuum hose marked with the green arrow. Don't break it or the car will have a fit (I believe it controls the evaporative emissions system).
Next you must remove the three screws holding the lower cowling on (see yellow arrows in pic below). This is where a socket extension would come in handy as there is very little space between the cowl and the metal under the windshield.
Now that the cowl is removed you have access to the screws holding the IMRC on, as well as the PCM and the cabin air filter (under the windshield behind the strut tower).
Disconnect the wire harness to the IMRC. It has a small push clip on the firewall side. Push it in and pull the harness off. You should be able to do this with your thumb and index finger.
The screws for the IMRC are diagonally opposite each other and require a T30 torx bit. The lower one might be a tad difficult to reach.
Remove the screws and pull the IMRC out. Mine fell out (see pic) with very little effort. Not good for a vacuum seal!
Now, use the screwdriver to (carefully) remove the old gasket. Once out of the groove it should slip right off.
Now you need to remove the gasket from the donor oil filter (or if you have the OEM replacement just grab that and skip to the part about installing the new gasket.)
The new gasket should be the same size around as the old one. If it's thicker around (like mine was) you will need to cut it so that you can get the IMRC back in the manifold.
Next, slide the new gasket on the part and seat it in the groove. If it doesn't sit flat it might need trimmed or you might need a slimmer gasket .
It might be a good idea to lube the new gasket before reinstalling the part with some sort of grease or lubricant (not wd40!!) I used heavy weight gear lube as it was all that was available. (see bottom of post for update)
Now you can reinstall the IMRC (be sure to align it). It might take some pressure (not excessive!) to get it on but that's good! It means you have an air-tight seal.
Now all you have to do is reconnect the wire harness and reinstall the cowling.
And that's it! The car might drive funny the first time after this fix but that is because the fuel trims are now incorrect. The computer will adjust them over the next few times you drive the car. You can also force it to relearn the trims by resetting the computer. Simply disconnect the battery negative terminal for a few minutes to clear the PCM memory.
Note: This fix is only temporary and will most likely wear out. The best thing to do would be to replace the bad gasket with another OEM one. But if you are cheap like me (and the Ford dealer is closed) this will work fine.
Update: So I had the IMRC out today. It wouldn't pull straight out so I had to twist it a little to break the seal between the gasket and intake manifold. Almost 4 years and I still have an airtight seal! Not bad for a quick hack fix. I lubed the gasket with wheel bearing grease before reinstalling. Here's hoping it makes it several more years!
Edited by Angrod, 30 November 2014 - 09:51 PM.