[header] How to check engine vacuum hoses [title] Check each hose for bulges and swelling. [step] If a hose feels soft or spongy when you touch it, this can indicate damage caused by your car's oil. [substeps] A swollen hose that is cracked and hard is often caused by heat damage. 
These hoses can be too close to heat sources under the hood or it may be the result of overheating. Bulging hoses can also be caused by electrochemical degradation when there's a coolant leak dripping onto hoses.