So this started essentially overnight. The day before, it was running great. The next morning, it was cold and I started it up, low RPMs, and it bogged down and died. I could keep it running with giving it gas. I got a ride and when I came home, it had been sitting in the sun for a few hours, and it started up perfectly and ran great. Problem kept occurring with cold starts. Check engine light pops on with the problem. I ended having a bad battery so I got a new one, problem improved but didn’t go away. I cleaned out the throttle body really good, replaced the TPS and IAC. I replaced the upstream o2 sensor, and fixed the air fuel mixture and was running good. Problem returned with cold starts. When it sits in the sun for a while, it’s runs right as rain, throttle response is right, the power is right, it eventually stumbles and check engine light comes on, but RPMs and idle remains good. My current codes now are 35, 14, and 52. I’m considering replacing the MAP sensor because air fuel mixture is kind of it’s job. I was wondering if you guys have any other ideas, I would appreciate any input. The exhaust manifold does have a couple of leaks, but I don’t know why that would suddenly cause a problem, considering it was doing fine in cold weather before all this.

 

Code 35 is the IAC. Code 14 is the coolant temp sensor, which could very well explain a cold start problem. Grab your meter and test it. Should be roughly around 30k to 36k ohms at 32*F, and under 1k ohms once fully warmed up. It should be good if you're in the ballpark, as the FSM gives a wide range. Also verify the wiring to the sensor isn't broken or shorted to ground anywhere.

 

I will do that tomorrow, thank you. I replaced it a couple months ago for a different starting issue. The plastic plug that’s inside the brass fitting does rotate, not sure if that means it’s bad but I don’t recall it rotating before.

 

• Okay, so I’ve been thinking. So if there’s leak on the exhaust manifold, that would let more oxygen into the system tricking the o2 sensor that the oxygen is coming from the engine, so it’s telling the PCM to put more fuel, causing it to run rich. Crazy or possibility? Because exhaust manifolds are kind of pricey

 

Exhaust headers are cheap. And a pretty quick job on the 4.0. The IAC will cause cold start issues, typically they die and get stuck in one position, sounds like yours got stuck in the normal run position since the Jeep runs fine when warm. The computer is throwing that code for a reason. Just because it was replaced doesn't mean it's good. They can be bad out of the box. Typically OEM is the way to go on the IAC, same for the coolant temp sensor. I stuck a Standard Motor Products IAC on my Jeep in a pinch. It lasted about 6 months then died on my way to work popped a check engine light for that code when going around a corner.

We know there are issues with your IAC and CTS so lets address those first before throwing parts at a problem that may not exist. Check your wiring for broken or frayed wires if you really think your sensor and IAC are good.

 

Right on the money.

But, like downs said, Fix Known Problems First. Always.

 

Alrighty, thank you both. I ordered an IAC from 1A Auto, I’ve heard that they’re reputable and the part had good reviews of longevity. I found a CTS from rock auto. Those should be here next Thursday. I think I’ll take care of that exhaust manifold next paycheck. I do appreciate all the input so far, will report back with results. Thanks guys

 

Just an FYI, be careful about aftermarket sensors. I don't know if the CTS is a problem, but the crank and cam sensors, and the O2 sensors, must be Mopar/NGK/NTK. Any others have a really bad track record ranging from dead out of box to not-quite-right out of the box, to lasting a few minutes, weeks, or months before failing. Really, they can be that bad. Dunno why, but there is plenty of experience on this board to back that up.

 

Yup. NTK/NGK made a lot of the sensors for Chrysler around our Jeep's timeframe. Pretty much the only brands ill use right now are Mopar, NTK/NGK, and Delphi.
subject to change of course Because of the global market these things change constantly. Im pretty sure Timken has the unitbearings for our front axles built on China now for instance. Theres been some grumbling about a quality drop off on those over the past 6 months to a year.

 

Alright, reporting in. I did the exhaust manifold today, and put in the new IAC and CTS. Problem has improved but not gone away. I got a cheap MAP sensor to try to see if that could be a problem. Not sure. Only CEL code coming up is 35

 

Check for other vacuum leaks.

 

Will do that. So I got another idea, there’s another temp sensor on the intake manifold (looks identical to CTS), it looks pretty old. If it’s on the intake manifold, wouldn’t that cause issues with sensing colder and warmer air if it was bad? Any idea what the proper name is?

 

Manifold Air Temp (MAT) sensor. It has the same resistance scale as the CTS. I think might even be the same part number?

 

It's not the same part number but does use the same resistance values as the CTS. It's also called the IAT (Intake Air Temperature) sensor according to the FSM.

https://www.rockauto.com/en/catalog/...re+sensor,5072

If you don't want to go straight OEM I'd at least go with the NTK sensor. Cheap parts store sensors can have you chasing your tail trying to solve issues.

Here's the resistance chart if you want to do some troubleshooting instead of just tossing parts at the issue.

 

Thanks for posting the chart again. X2 on testing instead of replacing. Especially for something as easy to test as a temp sensor.