An International Jugaar
I have been facing a problem recently. A certain rattling /hissing sound coming from the engine bay 1NZ FE. Couldn't be diagnosed by mechanics. Showed it to two, and talked to another on the phone (he works in Toyota Rawal). All three were of the opinion that I should use 20w50 and rattling would disappear.
I thought of a vacuum leak issue (due to hissing). But only symptom of that was decreased acceleration no check engine light, misfire or stalling. Noise seemed to be coming from front side of engine bay but vacuum hoses seemed to be fine. Then visually inspected intake manifold myself, which revealed this:
The problem area was perhaps this slit opening in the manifold:
So I thought that the intake manifold is sucking more air and engine was getting too much air and so a lean mixture. And of course the hissing sound specially during acceleration. So the manifold needs to be replaced.
Interestingly, an online search revealed that it is a common problem with Corolla and Camry engines where the baffle inside intake manifold becomes loose and starts rattling against the chamber. And people have been drilling and fitting small sized screws in the manifold baffle to fix it (basically its looseness):
https://thewikihow.com/amp_video_yDbV-09I0Pc
I couldn't believe myself. It's an international Jugaar that I just found. Some of you might be aware of this but new thing for me. Though I don't know if it really works but most of the users tried and were happy with the results.