[Bruckner]

Here's an interesting cookie for you guys. As I was doing the airbox mod tonight, for kicks I decided to try out my new endoscope to look inside the intake manifold, especially after reading on this board that some members took it out for a clean and reported improvements. I was initially happy to see that my intake looks very clean everywhere I could get the camera to go, until I hit this spot which seems to show some pretty serious cracking. I'm not 100% sure but I think it is the section of the intake that is directly below the 4 intake runners.

 

Is this a nothing burger, or something more serious?

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[lbpesq]

Looks like varicose veins.  Of course it is an old car!

 

(sorry, couldn’t resist)

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[ds968]

Heck, it looks more like stuff one would see in a colonoscopy image..    :wacko:  :blink: ..   joking aside,  I have no idea if those cracks are something to worry about, of if they're just normal wear an tear which may not necessarily mean impending doom..   Is the intake manifold a NLA part ?     

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[J.Elenbaas]

To me it looks more like built up dirt from some kind of material, try to take it off and clean the manifold.

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[Bruckner]

Yep, rich topic!



The part is available new for about 700$.



It is odd that the internals look like new yet this one area has degraded, I would imagine because of vibration. My concern is that it will only get worse and small chunks could theoretically break away and damage the engine. I don't remember reading about such an occurrence reported on the forums.



Could be that they're all like this passed a certain age, this is a 145,000 mile car!



It's hard to inspect under the manifold, I assume cracks that go all the way out would cause such a massive vacuum leak that the engine would run extremely poorly, which it doesn't. Still worthy of further investigation.

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[ds968]

“ My concern is that it will only get worse and small chunks could theoretically break away and damage the engine “

 

Indeed !  

 

Just becuase there are no reported cases on the forum, doesn’t mean it hasn’t happened to others ( who might have posted on RL or other places ) or that it can’t happen.  

J Elenbaas could  also be right, although what kind of dirt / impurities could amass to that degree ?!  Seems like a lot , even for 145k miles… but then again,  I’ve never seen the inside of an intake manifold…

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[J.Elenbaas]

There are several vacuum tubes connected onto the intake manifold, so it could be coming from oil fumes for example.

Hope it's not something worse than only fumes...

 

Anyway, after all those miles this is not strange. just don't use any kind of cleaner without taking the manifold away.

 

Otherwise particles can drop indeed in the between the valves and/or in the engine to create damage.

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[Waylander]

I will have to dig out my camera and have a look, my car is at 165K

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[Bruckner]

I will have to dig out my camera and have a look, my car is at 165K

That'll be interesting!

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[Cloud9...68]

I will have to dig out my camera and have a look, my car is at 165K

Miles, or kilometers?

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[Waylander]

165,667 miles, but Im way short of my friends iris blue sport at 225,000 miles



Just need to find a working laptop now, all been unused for the last 2 years now the batteries are all dead

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[paulzebo]

Just a temperature difference and gasses given off between the molten aluminum and sand casting it was poured into. Nothing to worry about. 

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[dlearl476]

Just a temperature difference and gasses given off between the molten aluminum and sand casting it was poured into. Nothing to worry about. 

That was my first thought, too. Something between imperfection and manufacturing defect.

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[Bruckner]

A quick update on this as it may prove useful. I took the intake manifold out (to replace AOS seals) and found about a cup of fluid pooled in the bottom, and even more strikingly a very thick layer of gum all around the intake ports of the manifold. This engine wasn't breathing right. The TB to manifold seals were broken up and dried up coolant residue was evidence that coolant made it into the manifold. I had a wheel refinishing shop deep soak the manifold, came out as new, and the car has since recovered many lost hp. I also ended up bypassing the coolant lines to TB, I don't want water in there, even with brand new seals.

 

If you have a high mileage 968, clean up your intake manifold, it may transform your car.

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[tejon007]

Yes, you don't want coolant in there. However, you'll probably want the coolant line to the TB hooked up properly so the coolant can heat things up like it was designed for...



But, our money is on the leaking TB gaskets causing unmetered air to get into the motor, then the computer adjusting the fuel because the O2 sensor was showing a lean condition. Replacing the perished gaskets is most likely the reason for the better running motor.



However, if your intake manifold is actually cracked that's a problem and don't see where it's been fixed by what you described. Have seen plenty of steel exhaust manifolds cracked, but never an aluminum intake manifold. So, the "cracks" were just contaminants on the inside of the intake manifold??



Best wishes.

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[Bruckner]

The cracks, though unpleasant to watch with a borescope, appear to be causing no ill effect, they are observed on the inner surface of the manifold. I can only imagine the engine would run very roughly if cracks through the intake walls were allowing unmetered air to get into the intake.

 

I ended up caping the 2 coolant in/outlets on the TB, my understanding is that the heating is strictly to prevent icing on the butterfly rod in winter conditions, which this car has never seen and never will.

 

The restored power is no doubt due to the removal of the thick gunk impeding flow through the intake ports of the manifold. The car also sounds different now, oddly enough.

 

The only unresolved issue remains a jerky hunting cold idle, which smooths out as the car gets hot. I've been told many times I'm being very demanding on an old, high mileage car! I'll keep trying nonetheless.

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[Waylander]

The hunting is caused by wildly swinging signals from temp sensors, air flow, idle speed, they all try to compensate for each other,



Air leaks in the ICV and that also gummed up cause a lot of the issues,



Start by checking the values of the small blue temp sensor under the top hose, then clean the MAF with any kind of carb cleaner, just do not attempt to touch the fine hot wire, then finally dismantle the ICV and replace the o ring that seals the top from the bottom, and some silicone around the electrical plug while giving it a deep clean and lube



That should sort it out

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[Bruckner]

Interesting, I did all of this but can you explain where you seal using silicone on the ICV? Thanks

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[Waylander]

It leaks around the cable plug, and there is an O ring that seals the body to the base, mine was in about 10 bits on dismantling

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