Quote:
Originally Posted by Mike621
Today, I pulled off the intake manifold to replace the coolant, fuel, and vacuum hoses located underneath. I decided to do this when I realized all hoses I was interacting with in the engine bay had hardened and were fragile original hoses.
I found a decayed/cracked fuel hose off the FPR once I had the manifold off. Glad I decided to embark on this maintenance.
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If you removing the intake manifold, it is a good timing to check the variable intake valve on the back side of intake manifold. Air leaks may occur from there. It's right in the middle of the manifold. The valve connects the left and right banks at high engine speeds, and makes them independent at low engine speeds. If this doesn't work smoothly, high rotation will not run smoothly.
The valve is operated by a vacuum actuator. I would recommend applying negative pressure to the actuator to see if it opens fully.
Note: When I checked and installed it, I make small mistake. I found that the bolts were not tightened enough, causing air leakage and the idle speed becoming unstable.