No. Installing an aftermarket air intake does not by itself void a car’s warranty under U.S. federal law.
The Federal Trade Commission’s rule under the Magnuson-Moss Warranty Act, 16 CFR 700.10, bars warrantors from making the continued validity of a warranty depend on using only authorized parts or authorized repair service for non-warranty work. The rule names clauses such as “This warranty is void if … all replacement parts must be genuine ‘ABC’ parts” as prohibited and deceptive, because a warrantor cannot avoid liability for a defect that is unrelated to the unauthorized part. A manufacturer can require specific parts only if it provides them free under the warranty or has obtained an FTC waiver. The exception is damage the intake actually causes: a warrantor may exclude defects or damage caused by an aftermarket component, and it may deny a claim when it can demonstrate that the part caused the problem. In practice, a claim for damage the intake caused can be refused, while defects unrelated to it stay covered.
Source: eCFR, 16 CFR 700.10 “Prohibited tying” (Magnuson-Moss Warranty Act interpretations)
Image: Cold air intake tube with filter, by Ildar Sagdejev (Specious), CC BY-SA 3.0, via Wikimedia Commons.