2000 XJ Rough Idle

[derff96963]

I have a 2000 XJ with 4.0 I6 with a KNN FIPK. Other than that the engine is completely stock. What I don't like is just recently it doesn't idle very well. Its does idle and has never stalled on me but I just don't like how it idles. The other day I was stuck in traffic in some road construction and after about 5 minutes of not moving it started shaking pretty bad. Again it did not stall and it revs fine and has lots of power. I have checked and cleaned the throttle body and the check engine light is not on. I have changed the spark plugs with no change. I cleaned the IAC valve and it does seem to operate nomaly and the TPS tests ok to. It only has 61,000 miles on it. Anyone have this problem or have any ideas?

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).

[dingus]

i thought 2000's dont have spark plugs....?

[TwistedCopper]

It's distributers that they don't have.

[derff96963]

All cars have to have spark plugs unless they are a Diesel. I only have a pseudo Dist. It has a short shaft that sticks up a few inches and I beleve that's the camshaft position sensor on top. I just tried to pull any codes and and its says Pass no codes stored. It almost seems like it was going to stall when I just started it. I am just plain out of Ideas. If it was the fuel mixture which it what it seems to be that should trigger the CEL.

[XJNick]

Hi,

Does the rough idle occur based on temperature? driving duration?

-Nick

[derff96963]

Not Really, It does it sometimes and sometimes is doesn't. It doesn't seem to have much to do with temp except it does it less when it is cold but it still does it. It seems like the fuel mixture if off. Like on a carbed engine with the mixture just a hair too lean. It will idle fine for a few seconds then bog down for a second. Then be fine again for a few seconds. I just can't figure it out.

[XJNick]

Hi,

Check out the EGR system. Make sure the EGR valve isn't stuck open or opening at the incorrect times... if it is it could be the valve itself or the EGR solenoid triggering when it shouldn't be.

Another interesting test would be to install a fuel pressure gauge and monitor the pressure while you go on a drive...

-Nick