i have a 1996 volvo 960 2.9L I6

i had to replace my water pump so i had to take off the timing belt. i took the belt off and did what i needed to do and then put a new belt on and made sure the timing marks were all good. i rotated the crank a couple times to test then i started the car and everything was cool. i drove a little and then parked. it sat for about 3 days and then i took it out for a spin. i drove for about two minutes and while stopped at a red light i felt the car shut off and then on again almost instantly. the only reason i think it shut off is because i saw the gauges drop to zero and then return to where they were. then a second later the check engine light came on.

so im wondering if messing with the timing belt is the cause of this.

then i fooled with the car a little more and every time i turned it off the engine cooling fan on the radiator stayed on for a longggg time... and i know this might be typical for some cars but my car has never had the fan on this long (owned car for about four years). then after i let the car run for a few minutes the fan shut off (while engine was running) and now the temp gauge is reading cold and below (looks like it off). do i need a new thermometer? or what should i do about this

thanks id appreciate any advice

 

Logical to look at T belt... Make sure a tooth is not off. The fan issue should not be related BUT weird stuff happens...
Address the running first, see what happens with fan once car is running right.