Recently I've been having an issue where my 96 XJ will idle weird when the engine is cold and it's just getting worse. The rpm will fluctuate and if I try to drive it almost stalls. I've replaced the IAC and looked at the vacuum lines and they all look good. Once it's warmed up it has no issues and drives normal. What would cause this problem only when the engine is cold? Thanks!

 

I dont know whats going on but my first thought was the IAT sensor (Intake Air Temperature). Should be on the intake manifold. The PCM uses it, along with other engine sensors, to figure out how much fuel it should be feeding the engine on startup and idle. Engines need more when cold and less when warm. So, when the sensor reads cold, the PCM richens the mix. When the sensor reads warm, it starts cutting fuel. Cold starts may be rough with a choppy idle if it isnt getting the fuel it needs. Once the engine is warmed up, the engine runs fine as the fuel is where it needs to be. Its possible its getting too much fuel when cold.

Is this your issue? I dont know. But you can test it. Do that before replacing anything. Which wires do what im not sure, but i think there are only 2?



Also, the ECT sensor (Engine Coolant Temp) is another possibility. It works the same way as the IAT, and plays a role in how much fuel the PCM adds or takes away. I think the ECT was on the thermostat housing for 96. That is the one the PCM uses. The coolant sender behind the valve cover is for the gauge.

If you can check codes, i would do that as well.

 

It'd probably be worth cleaning your throttle body and verifying that the new IAC wasn't bad out of the box.

 

I cleaned the throttle body a couple times and only replaced the iac after cleaning the old one a time or two.

 

No codes but would cleaning the IAT be worth doing?