Hello.
1997 toyota t 100, 2.7 liter 4 cylinder, manual, 365,000 miles. Have noticed in the last few months when taking foot off gas get a bubbling jake brake sound from somewhere over on the passenger side of the engine. Not as loud as the big trucks of course, but way too loud for a small engine, can't be normal! Especially annoying when going thru town in 2nd or 3rd gear, but can hear in all gears when I slow down. Thx
Your description sounds like a leaky exhaust valve. You can do a Leakdown Test.
Or you could just buy one of those $10 adapters which one end threads into the spark plug hole and the other end fits an air compressor fitting and after bringing each cylinder, one by one, to TDC, put about 100 psi into that cylinder and then listen for a "hissing" sound at the tailpipe
thanks for your suggestion. I'll look into that. Not real mechanical, but will mention it to one of my mechanics. I need to look up what is a leakdown test! thank you