I have been chasing what I believe is a vacuum leak unfortunatly to no avail.
03 3.0 93K I"ve changed the breather hose, and IMT O-rings but still have cold start misfire & limp mode. Brake Booster Hose seems to be Ok " can't hear any hissing. Does anyone have an idea what to check next?
I suppose I should change the plugs and manifold gaskets next but, don't think that is what's causing the problem.

 

Have you scanned the codes? If it is one or two cylinders it might be coils. Post the codes if you can and I'm sure you will get some replies. When is the misfire apparent? Idle? specific rpm's?

 

I've gotton a bunch of codes...P0300,P0301,P0304,P0305,P0306,P1313,P1314, P1638 and P0420.

Cold start is when it won't idle. When it's warmed up it runs fine. This thing is an animal when its cold.

 

Almost forgot..P0171 & P0174

 

You're getting a lot of the same codes my car is getting right now. My first theory is that it's either the upper or lower manifold gaskets leaking. I'm not sure if you know what the P codes mean, but I will provide that information for you or anyone else reading this. The P0300 series are misfires. 300 is random misfire. The 301, 304, 305, and 306 are misfires in cylinders 1, 4, 5, and 6 respectively. p0171 and 174 mean bank 1 and bank 2 are too lean respectively. p0420 is catalyst efficiency below threshold bank 1. P1313 and 1314 are misfire rate catalyst damage. P1638 is CAN Link ECM/INSTM Circuit/Network. I would agree with you that most likely what you have is a vacuum leak. Did these codes all show up at once? I'd replace upper and lower manifold gaskets first at this point. While you are in there pull the spark plugs and check the condition. If it's been a while since you replaced em, you might as well do that because who knows when the next time you'll have the manifold off. Also switch the coils around. Make sure you take the coils from the good cylinders and put them on the cylinders reporting misfires. And vice versa. See if the code jumps. If so you know you have at leas a bad coil(s). The fact you say it runs better when it's warm points to a vacuum leak. When the engine heats up, everything expands, including gaskets. This may seal a leak and cause the engine to run better. Let me know what you find out.

 

No these codes came up at different times as I was attempting to source the vacuum leak. My goal is to fix the leak first then see what, if any codes I get. Plugs, Manifold gaskets are next.
There is a breather line that runs from the rear valve cover to the TB that has been repaired once, so I will replace it when I pull the manifold. Hoping that is the problem.

 

But youve already said the brake booster line and intake gaskets you dont think are it!!!
Sorry but that is exactly what i would fix if youve already done imt orings and pcv hose. You can heat shink a sleeve over the brake booster ck valve to seal it, and replace the upper and lower intake gaskets. All replace the plug while you have intake off if youre even 20k miles close to a 100k. Youre right there and done the work to reach them. Its foolish to not change them out now...

 

I agree Brutal, I'm at 94K so I will change the gaskets and plugs. The reason I believe the Brake Booster hose is good is that it is the new design with the heatshrinked check valve.
There is a second line coming off the manifold that goes to somewhere near the firewall. Any idea what that is???

 

Ahh, see alittle more info always helps. The other tube is the purge line from the evap. System..
Change the intake gaskets upper/lower. You did chang ethe imts oringsa to the new green ones havent you?

 

Yes, the IMT o-rings have been changed as well as the PCV hose. I will replace the purge line that you mentioned when I pull the manifold but could that be the source of the vacuum leak???
How difficult is it to change the lower gaskets??

 

once the manifold is off it is very easy to replace the lower gaskets. I think its 4-6 bolts and you can lift the fuel rail assembly, or fuel manifold as I have heard it been called and one or two electrical connections on the fuel rail itself and the whole assembly should easily tilt up towards the back allowing easy replacement of the gaskets

 

Ive never seen the pruge line leak, change the gaskets first since theyre harder than everything exposed ontop of the engine. The quick disconnects that both of the pastic pipes go into also can leak, but again you can deal with that later

 

When you remove the two black plastic portions of the fuel rail assembly, pay attention to the bolts on it. Some of them are holding the two pieces together, and some of them are holding the assembly to the engine. You don't need to separate the halves.

 

Thanks to all. I'm going to have my mechanic put a smoke machine on it. This should tell me what's leaking. I'll keep you posted on my progress. Hope this sorts it out.

 

Why, waste of money imo. Already told you what it more than likely needs, just diy it, with the engine cold, spray the intake gasket area with water, carb cleaner, brake cleaner etc...lekaing intake gaskets will really show themselves and you can save the money for the parts

 

You got two people telling you it's most likely the same thing. It'll cost you about 30 dollars in gaskets, plus about that in spark plugs. You've got a very good chance at solving your problem for less than a hundred bucks and maybe 90 minutes of work, if that. If you need to replace your plugs anyways, what's the harm in replacing the gaskets while you are in there?

 

It won't cost me anything. My friend is a mechanic and offered to do it. I plan on changing the gaskets, plugs anyway. Just thought I would be sure there are no other leaks. Thanks for the help

 

most likely your IM gaskets like they said. I would reccomend changing both upper and lower gaskets while the manifold is off.Ive seen them all go bad(especially the yellow ones). If you for some reason still get misfires after you change the plugs and coils, then your going to need to clean the fuel injectors. We are constantly cleaning 3.0 and 4.2 fuel injectors at the shop for misfires especially for random/multiple misfires.

 

Oh and brutal is right, thos quick disconnects plastice pipes can also leak

 

lol nothings free, bring him at least a 12 pack of imports