308QV back fire cold

Hello all, I have a question, which sensor does the 1984 308 QV get its engine temp reading? Is it the one on the coolant tank, mine reads open with a DVOM. My car backfires through the intake on cold starts while stepping on the accelerator, other than that it runs fine once warmed up. I thought it was the WUR at first so I took it apart and it looked ok inside so I reassembled it and reinstalled it. It seemed ok for a couple of days after doing this, fine during cold start and ran like it had before, then after sitting for a weekend the same condition returned. Initial start up backfires bad though the intake. Seems like you guys have alot of experience out there, can you throw me some advice. This CIS stuff is new to me.