I had high blms so took out trusty smoke machine. First leak was at egr valve. Replaced the valve, now I see lots of smoke coming somewhere from rear of engine, possibly the intake. Is there anything I can smear on it to seal it, at least temporarily, to confirm where the leak is? I was thinking maybe plumbers putty. Something more permanent would be preferred. Car idles like crap until it is warmed up, and got a code 44 lean O2 sensor. Thanks.