I have a '99 XJ Sport with around 154,000 miles that I bought last spring. Complete tune-up in the summer..plugs, cap, rotor, coil, etc. Runs great. However, now that the weather is cold, and it is left outside overnight, it will not stay running when it is started in the morning unless I keep my foot on the gas and keep the idle around 1200 rpm. Once the engine warms up, everything is fine. If it is kept in the garage, 40+ degrees, it starts fine. After work it starts fine. Only cold mornings ???? Thanks in advance.

 

Could be a marginal battery. I found out the hard way on my 99 that it does not like a low or marginal battery. I learned this when I had to get it started after the battery ran down. It would sputter and idle horribly unless I kept my foot on the gas. Even jumping it to give it a boost didn't help. checked everything and changed a few things. Finally gave up and put a new battery in. Problem solved. No idea what is so sensitive with the battery, but it is. If you search, you'll find a lot of similar stories. Not sure if the IAC comes into play when it's cold. The IAC determines how much air is let in while idling. If it's dirty, I could see it letting in too much air when it's cold which would affect the idle for sure.

 

When you apply some gas and keep it running (around 1200 rpm), does it still run poorly? or is it relatively normal?

If it is running poorly when you "keep it running", that points more to a low voltage problem, which can be brought on by corrosion in battery connections and ground connections. Sometimes they will be bad when the metal is cold and small, but as the metal expands the connections improve and things get back to normal.

If it is running normally when you "keep it running", that points more to an IAC (Idle Air Controller) that is failing or sticky when it is cold, and starts to work as it warms up. Its function is to moderate the air going into the engine via the throttle body when at idle (ie. your foot -off- the pedal).

 

1. Any check engine light? If so, retrieve codes and post the exact codes here for comment.

2. As mentioned, start with "load testing" of your battery. The engine management system is indeed fussy when electrical isn't well. Any parts store will load test your battery for you for free. I am not saying this is your problem, but I am saying that it is one of the first things any shop would do if they had your XJ.

3. If all above checks out, then I would start with the engine management sensors. Clean the idle air control and throttle body, test the throttle position sensor, test the coolant temp sensor as well.

4. Wouldn't hurt to verify fuel pressure on a cold morning as well while the engine is symptomatic. Would want to see if the fuel pump is delivering the 49 psi, plus or minus 5 psi right away in the morning on a cold start.

TEST your way to an answer.

 

1. Battery (Interstate) is less than 2 years old. All connections are clean and tight.
2. No codes present.
3. With foot on gas, idling at 1200 rpm, engine idles smooth. Accelerates smoothly when engine warms up.

 

Wouldn't hurt to check your temp sensors (and connectors/wiring) in case one has drifted (spoofing the ECU into thinking it's a different temp). Normally a vehicle set's the outside temp it 'believes it is' based on the initial temp reading. THey can be ohmed out and compared to an ambient temperature scale. There should be two, I'm not sure which one for the ECU. I had one on a PU that drifted and when it got cold it wouldn't run for crap. Ran fine rest of the yr though.

Water in the fuel? (frozen filter ...not letting fuel flow??)

Just tossing out ideas here....

 

Being less than 2 years old does not rule out a failing battery. Ask any shop or parts store how many batteries they see fail prematurely. It's way more than you would think.

 

If it was a voltage/battery problem it most likely would not be idling smoothly (even with foot on gas).

Are you saying that it does -not- accelerate smoothly when the engine is cold?

 

Like others have said, I would test the battery. Had the same problem and it was the battery

 

25 degrees out this morning. Started right up and ran smoothly. Going to clean the throttle body and IAC this weekend. Thanks for all the replies.

 

That would be my suggestion at this point.