Honda Del Sol - B18B1 motor (same as 90's Acura Integra LS/GS)
I have two rattles I need help diagnosing. The problem is, they only occur during conditions that I can't replicate with the hood open, so I can't easily tell where they're coming from.
Rattle #1: From my driver's seat it sounds like it's coming from the transmission-side (passenger side) or maybe from the middle of the engine bay, perhaps the throttle body or even clutch/flywheel. I can't rule out that it isn't one of the valves on the far side of the engine either, as it's really hard to tell where it's coming from. It occurs when at high vacuum, 3500+ RPM when letting off the throttle, only when the throttle plate isn't completely closed (typically 100MPG on MPGuino and decelerating, but not quite closed enough to cut off the injectors). The sound resembles a loud metallic chattering and made me jump the first time I heard it, a few days ago.
Is it possible for a throttle plate to become loose and rattle when it's almost closed? What else might I look at?
Rattle #2: Occurs only between 2500 and 3000RPM, sounds like it's coming from directly in front of the driver's seat, so water pump/timing belt/possibly valve-train/accessory belt area. I only hear this one when there's some load on the engine, revving it in neutral creates no rattle. It's a quiet rattle/chatter that sounds the same at low load as at WoT.
I'm afraid it might be the timing belt tensioner rattling but I'm puzzled as to why it would rattle only under load and between specific RPMs. I'd replace it tomorrow except I'm in the middle of a move and money is particularly tight for the next few weeks. What else in the area might behave this way?
^ Sorry about poor engine bay image. I don't have any taken in the past 2 years. Rattle #1 sounds to be coming roughly from the red circle, while #2 is roughly near the blue circle.
Despite these rattles, the engine appears to be running great, just did 37MPG 120 miles cruising at 65, not drafting.