Ok so I just bought a 98 Cherokee on Saturday. The thing drove great but needed a battery due to sitting a while. So I put the battery on the tender over night. The next morning I went to start it and it wouldn't start unless I applied a slight amount of throttle pressure. After it started it would die out, no idle. So I replaced the IAC valve and Battery. It now idles and starts fine....

Now I have a new problem that has come up after fixing those. When I drive it after a cold start it's fine for about a minute then starts to misfire and backfire through the throttle body. It happens for 30 secs or so then after that it's good and no issues till I start it up again. I did notice that within a mile and a half the temperature gauge was almost at 200, but the air from the vents was still cold.

 

Step 1. Complete tune up get that in the record book.

 

^^This would be the first thing you would want to do^^
As for no heat from the heater. you should start with a good back flushing of the heater core. Flush it in both directions. Once the water start to come out clean flush a few more times in both directions to make sure that all of the crud is removed.
Welcome to the forum.

 

Thanks. I'm gonna look at the plugs. But the heat thing was a reference that maybe the gauge is showing operating temp when really it's NOT. Bc after I drive it 10-15 minutes the heat is hot as can be

 

Congratulations on the Jeep! If you haven't changed ALL fluids yet, now it's a great time to do so!

That's very possible. The 1997+ PCM uses a single sensor to drive the gauge in the dash as well as to set the fuel mixture. If it thinks the engine is warmer than it actually is, it'll run it lean and backfiring can occur. That said, your Coolant Temperature Sensor may actually be okay, as the PCM has to compare everything to a reference ground.

If, after your tune up, this problem is still occurring, I suggest you test the CTS versus known values with a multimeter. You can do this however you like as long as you can verify independently the temperature it SHOULD be at (pot of water for example, or in the engine while using an infrared gun to check temp).

4.0 COOLANT TEMPERATURE SENSOR: Temperature-to-Resistance Values (Approximate)

212 farenheit 185 ohms
160 farenheit 450 ohms
100 farenheit 1600 ohms
70 farenheit 3400 ohms
40 farenheit 7500 ohms
20 farenheit 13,500 ohms
0 farenheit 25,000 ohms
-40 farenheit 100,700 ohms

Again, the importance of a proper tuneup can't be overstated. Fresh Champion RC12ECC or NGK ZFR5N copper plugs gapped to 0.035", quality wires, and a distributor rotor and cap with brass contacts are key.

 

Oh! I thought you meant you had no heat at the heater. My 98 takes about 4 or 5 mins to get up to normal operating temp which is around 210degs. If you are not sure if you temp is right you can verify it with a I.R. temp gun aimed at the t-stat housing.