I need help eliminating what I think is a vacuum leak.
Car: 1995 E320
History: about 4 months ago I replaced head gasket and intake manifold gasket/seals. The car ran great for a month then started idling rough
Symptoms: When cold the idle is both rough and surges. After 2 minutes the surging is gone but the roughness is still there. After 10-15 minutes or when the engine is fully hot the rough idle is much less severe, sometimes not noticeable.
Under acceleration the engine is smooth whether hot or cold.
My diagnosis: I can hear a distinct hiss from under the intake manifold, seems to come near cylinder 3-4. I sprayed carb cleaner in that area where the manifold meets the head and the engine surges.
I replaced the vacuum hose that is in that area (both the small tubing vacuum hose and the shaped rubber hose that goes from under the manifold to the Throttle body). Therefor I am pretty sure the leak is coming from where the intake manifold meets the head.
My question is how do I tighten the manifold bolts (Allen head). First, it seems there is only one bolt between every other cylinder (spaced quite far apart - how does it manage to keep a tight seal). Second, it seems to be impossible to get to. I couldn't manage with any of the flex attachements I have.
If I manage to tighten the manifold bolts and it doesn't cure the leak, Any advice would be welcome.