I guess we are all providing sage advice without asking the relevant questions. (OK - It never stopped us before!)

Just how long are you leaving it to warm up and what temperature are you starting it at? It's going to take a lot longer to warm up if it's 40 degrees out, compared to 70 or more. In Florida, where we don't fly often it it's below 70, 30 seconds to 1 minute will be enough. If it's something like 2-3 minutes you have problem. I always warm up the engine at a fast idle. It will take an age at full idle to come up to fulll operating temperature. What are your conditions anyway?