Every once in awhile since I installed the TVT-whatever kit (CAI, ported intake manifold and throttle body, bigger injectors) on Friday, September 24th, I've noticed that when I start the car, it initially idles around 1900 RPM which is much higher than normal. After driving it for a few minutes, the idle will drop back down to normal if I'm stopped at a stoplight but then if I'm waiting for any significant amount of time with the car out of gear (longer than 3-5 seconds), I notice that the RPM will creep back up from 800 RPM to 1800-1900 RPM and flutter back down to 1100-1200 RPM and then back up to 1800-1900 RPM again. I've noticed it'll do this randomly on my 25 mile commute but when I pull into the garage at home, it just idles normally again around 800 RPM.

Again, when I'm stopped at lights, with the clutch depressed and the transmission out of gear, my right foot is off the throttle completely and the engine will begin to idle higher than normal then drop back down to just above normal, again and again.

Does anyone have any suggestions as to what this might be? My immediate guess is that the stock ECU still trying to learn the fuel trim with the new injectors. I've not experienced any drivability issues or other problems since the install and no CELs have appeared on the dash, but I don't remember my XF idling strangely like this when it was bone stock.

 

I noticed this problem on Monday and it happened again yesterday but it didn't do it on my drive home today. Not sure what the deal is.

 

I don't know what it is but it sounds like a leak to me. Could be a vacuum hose or throttle body or even the intake manifold that has a leak. If you can check for error codes that could give you a clue.

Les

 

Expose the throttle body inlet.

Start the car and then take the palm of you hand and slowly cover the TB. If Iam right your car will slow down and idle at a normal sort of speed. Id bet you you there is more than one small leak.

To detect the leak, you can spray carb cleaner around the intake and see the effect on the engine speed.

Woody

 

woody's right on as usual....you have a leak somewhere on your install....go back through all you did....retrace your steps so to speak...

 

Thanks for the suggestions! I'll take a look tonight and let you know if I find anything amiss. It was idling at 2000 RPM when I pulled into work this morning so I definitely need to address this.

 

Check your vacuum lines around EGR valves too. Easy to bump off when messing with intake stuff.

 

I checked all the vacuum lines and they were all connected. Nothing loose from what I could tell either. A few days after I first started this thread, the CEL came on and the RPM flutter has continued. I haven't had time to take it in to AutoZone to have the code read yet but this morning, the check engine light went off and the car seems to be behaving normally again. I haven't noticed the RPM flutter at all today.

On the other hand, my gas mileage took a serious dive since the CEL came on. I'll be lucky to get 300 miles out of a tank when I usually get 370-380 miles between fill-ups.

Wouldn't the engine be running a bit on the lean side if there was a vacuum leak somewhere in the intake track? Or is the ECU overcompensating for the increase in air volume by running rich?

In any case, I'm now thoroughly confused so I'm going to hook it up to an OBDII scanner and see what, if any, codes come up.