misfire at idol with thermostat

[sonissan]

so i recently bought a 1996 hardbody with 98k in it for 1500 bucks and it has a misfire at idol with a thermostat in it but if you remove the thermostat it is fine the timing chain was recently replaced and a tune up was done. anybody ever have this problem?

[Frankie Pintado]

Look for vacuum leaks. It will run colder with no thermostat, maybe even stay in closed loop, meaning it will be adding extra fuel to the the mixture. When it reaches operating temp (with thermostat) it goes into open loop it switches from using speed density formula to using the MAF to calculate the fuel mixture. If there are vacuum leaks after the MAF, that air is not taken into that calculation. Also suspect dirty MAF. If you disconnect the MAF, that will bring it back to speed density formula. If that makes it run better, my theory is confirmed.

[sonissan]

checked for vacuum leaks founs nothing looked through the stack of receipts and found there is a new maf on the truck