sometimes when i pull up to a stop light the rpms will drop very slightly for a second or 2 then return to normal.
i sprayed all the vacuum lines and fittings with carb cleaner with no change in idle speed. I checked the 2 small o-rings and they appear intact.
I replaced the upper intake gaskets about 6 months ago...if one of the lower intake gaskets was failing could that cause the idle issue?
I also did a visual check on all the hoses (including underneath the hoses) and all seems intact

 

the rpms go from 740 down to 500, back to 740, down to 500, back to 740..then it stays at 740

 

About two weeks ago I posted the exact same issue.
I was able to cure mine quite easily. With all the maintenance I perform on my 05 jag the one thing I always forgot to do was change the air filter. Would you believe I had the original air filter?
When I peeled it out it was so clogged I was surprised the car started at all.
Putting in a new one cured my erratic idle.

 

Got the same problem. Did you find the reason?
No help in my case.

 

Yeeran, I would recommend getting a little bit of throttlebody cleaner (not carb cleaner) and cleaning out your throttlebody. In short, use the straw that comes with the can, spray the inside of the throttlebody (while holding it open) and if you see brown, spray it down. The fluid coming out of the can should wash away the brown. Keep spraying till the brown is gone or you have gone through a majority of the can. Make sure to spray the edge of the metal disk that you are holding open to get rid of the gum that has formed there. Odds are, your idle issue is the butter fly valve (that metal disk) is sticking and the motor has to drop RPM wise down a ways before the signal becomes strong enough to the throttlebody to overcome the sticking valve.

 

Harryc...the air filter I have is almost new so that's not the problem, and it does not do it all the time....maybe 75%

 

Had the same issue. Cleaned throttle body. MAF sensor multiple times. Replace IMT o-rings. Check for vac leaks.Could also be bad fuel injector per service bltn. Same issue. Was going crazy. Mine disappeared when I switched from using costco gas to another brand. Tried 2 different stations and 4 fillups. No dropoff or miss at idle and no hesitation. Went back to costco and issue came back.

 

Dvd711...what is the injector bltn?

 

iownme...sorry it was a tsb or technical service bulletin which advised possible fuel injector.

 

i think i fixed the occasional idle issue.
i just replaced the pcv valve and the brake booster to intake pipe and one way valve, and the issue has not happened since.
originally i had sprayed both areas with carb cleaner while the engine was running and the idle did not change...so don't be fooled into thinking these areas are ok just because they pass the carb cleaner test.
Hope this helps

 

pcv valve was $23 and pipe+valve was around $60
both parts came from coventrywest.com

 

Mine did that just before the fan module went out. Hasn't done it again since I replaced it.