Every time when I cold start the car, the engine revs at 1300-1500RPM and drops down to below 1000 after 30-50 seconds (that's when I shift from Park to Reverse).

Is this normal???

 

Mine does a similar rev at start, but I would have to review it specifically to tell you if its in the exact same range as yours (1300-1500) - It then idles at 600 on the nose in drive (according to the tachometer) I am not 100% sure, but I feel as if my car revs a bit higher after I cleaned (or partially cleaned) the throttle body. It was truly black around the butterfy plate, and on the engine side of the plate, and even though I had some quality 3M Throttle Body Cleaner, I don't feel as if I got it as clean as I would like.

It's since that operation last weekend that it 'seems" to rev a bit higher on startup, but that could be imagination. I have only owned the X350 for a few weeks, but the 4.0 Liter in my X308 also reved on startup. I am pretty sure its working as designed.

Anyone know a thorough way to clean up the intake? I cleaned my airbox and replaced the filter - I also have run 2 containers of Chevron Techron (treats 12 gals., so I use 2 per tank 2x. I am afraid to use any more for thinning the oil with the stuff. (I am considering a K&N, but want to make sure people aren't reporting dirty (as in oil covered) MAF sensor with a K&N in the airbox - On some car designs its a real problem. Anyone?

 

Read OBD live data such as fuel trims (hot engine, parked, at idle & at 2500rpm) as high idle is often due to an air leak - which trims rule in or out.

 

mine does that and settles at 600.

 

Mine has always done this also.

 

Same as mine as as well. The S-Type does it too. My previous car, a modern Pontiac GTO did it especially on cold days. It would sit close to 2k for around 10 seconds and smell like raw fuel before it warmed up.