Starting Problem



Hi, I have a 1991 Jeep Cherokee Laredo with the 4.0L 6 cyl engine and an automatic. When cold, it stumbles when started and if you don’t add gas, it quits. When warm, it is fine.


When was the last time you did basic maintenance, like plugs, filters etc.


New K and N AC, plugs good Platinum


I would look at the coolant temperature sensor CTS. Check the resistance to make sure it is calibrated to the engine temperature. The resistance should drop as the engine warms up.


I too had a 91 Jeep and it was hard to keep running after first started. Changed plugs, wires, distributor cap, rotor, cleaned fuel system and most importently looked for and found a small vacuum leak. The latter fixed the problem. Also started adding Marvel Mystery Oil to the fuel, it helped the starting.


[b]Another thing that can cause this problem is a defective Idle Air Control motor.

When the engine is first started, The IAC motor lets just enough air into the engine to keep it running as the engine warms up. If the IAC motor fails to this, the engine will run very rich and stumble. When you step on the accelerator while this is happening, you open the throttle plate enough to allow air into the engine and the engine clears itself and runs smoothly.

Once the engine warms up, the IAC motor probably goes to the proper position for that engine operating condition and everything works fine.