A car purchase contract is valid only if it is signed, not stamped. According to the law, if the parties conclude a contract in the form of a contract, the contract is established when the parties sign and seal it, and the signature and seal have the same effect. Therefore, if the car purchase contract is not stamped, the contract is still valid.

Legal objectivity:

Article 490 of the Civil Code of People's Republic of China (PRC): If the parties conclude a contract in the form of a contract, the contract is concluded when the parties sign, seal or fingerprint it. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it. A contract shall be concluded in written form as stipulated by laws, administrative regulations or agreed by the parties. If the parties do not do this in writing, but one party has fulfilled its main obligations and the other party accepts it, the contract is established.