Rough idle when first started.

Atl XJ · May 5, 2005

My '95 4.0l/AW4 XJ with 105K on it runs really rough for a few seconds when you first start it up when cold. If I turn it off and turn it back on it usually clears up right away. It only does it when its been sitting over night. The weird part is that it doesn't do it on cold mornings, its just starting to do it now that the weather is warming up. Its like the computer isnt getting the right reading for for it doesnt need to "coke" the engine like it would on cold mornings when its been sitting a while. It was cold the past few mornings and it ran beautifully on start up. Its when its in the 50s or warmer in the morning it does it, after that clears up it runs beautifully. Its had a recent tune up, O2 sensor, both the temperature sensors, fuel filter, basically everything in the CCV system has been replaced, catalytic converter, TPS, umm I'm sure I'm forgetting some other stuff I've replaced recently.

TIA, I'm stumped.

8Mud · May 6, 2005

The wifes 96 ran like a four letter word (a couple of weeks ago) when I first started it and would sometimes stall. If I could coax it for a minute, it would run just fine. On a hunch I dribbled a little penetraion oil into the IAC orifice, with the motor running and the problem disappeared. I´m gonna do a good TB cleaning soon.
The battery was also dieing a slow death, think a combination of low voltage at start up and a sticky IAC was the problem.

JoBo · May 6, 2005

Atl XJ said:
My '95 4.0l/AW4 XJ with 105K on it runs really rough for a few seconds when you first start it up when cold. If I turn it off and turn it back on it usually clears up right away. It only does it when its been sitting over night. The weird part is that it doesn't do it on cold mornings, its just starting to do it now that the weather is warming up. Its like the computer isnt getting the right reading for for it doesnt need to "coke" the engine like it would on cold mornings when its been sitting a while. It was cold the past few mornings and it ran beautifully on start up. Its when its in the 50s or warmer in the morning it does it, after that clears up it runs beautifully. Its had a recent tune up, O2 sensor, both the temperature sensors, fuel filter, basically everything in the CCV system has been replaced, catalytic converter, TPS, umm I'm sure I'm forgetting some other stuff I've replaced recently.

TIA, I'm stumped.

You've told us what is wrong! Replace the sensor on the thermostat housing. That's what tells the computer the engine temperature.

JoBo

Atl XJ · May 6, 2005

But I replaced it already. I originally thought that was the problem so I tried replacing it and it didn't make a bit of difference.

Atl XJ · May 6, 2005

8Mud said:
The wifes 96 ran like a four letter word (a couple of weeks ago) when I first started it and would sometimes stall. If I could coax it for a minute, it would run just fine. On a hunch I dribbled a little penetraion oil into the IAC orifice, with the motor running and the problem disappeared. I´m gonna do a good TB cleaning soon.
The battery was also dieing a slow death, think a combination of low voltage at start up and a sticky IAC was the problem.

I'll try that. My battery is at least a few years old (I dont know how old it was when I bought my XJ) but I don't think the battery is the problem since it runs fine when the outside temperature is low on a cold start.

8Mud · May 6, 2005

The battery may have been part of it, maybe not, noticed my battery voltage in the morning (after sitting all night) was a volt or two lower than other batteries I´ve checked. I know what appeared to be a sticky IAC, was most of the problem, just get a feeling, the IAC may have been starved a little at start up for juice (like it had trouble opening). Combination of weak/low voltage, but mostly just the IAC sticking a bit. Never did it in the winter, just started up this spring.
Just a possibility.

Rough idle when first started.

Atl XJ

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8Mud

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JoBo

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Atl XJ

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Atl XJ

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8Mud

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