Loosing low end torque when hot
 

This doesn't happen all the time, and there are never any codes stored.....

When the engine is cold, the 4.4 works just fine. Plenty of power and throttle response. But occasionally after the engine is up to temp I'll loose throttle response and torque. Especially noticable when pulling my trailer. I can run along at 70 with the trailer behind me, about 3,000 rpm, and have some throttle available to pull inclines. Other times at the same speed there will be absolutely no throttle response when I tip into the pedal.

On my 528 when I had the same problem I needed to replace the vanos seals but on that car it threw codes because the mixture was out of spec. No codes on this.

Thoughts??

How many miles? My first thought was torque converter...

I had the same problem 3 weeks ago ! My car ( 2001 x5 4.4) was very responsive and powerful when it s cold . But after 15 min ( when it becomes warm) it becomes sluggish unresponsive ( like i was loosing torque) so i did a simple tune up : spark plugs, air and fuel filter , f
Cleaning the fuel pump and the injector ,( i changed also the overflow coolant tank because it was leaking) . My x is now a lot more powerful responsive when warm. ( forgot to say that i didnt get any code)

Check also your cats. And your fuel pump ( when driving ). I read this somewhere :<< Some pumps will only fail after warming up, so they appear to work fine after they have "rested" for a while. This is the sign of a dying fuel pump motor>>

Trans and tq replaced 9,000 miles ago under warranty.

Full throttle accel is fine, so I'm suspecting the fuel pump is putting out correct volume and pressure or it would starve at high rpms under load. It's only the part throttle responsiveness that goes away. At maybe 3/4 throttle it's all back to normal power.

Plugs changed maybe 2500 miles ago, at 87,500 miles. They were original and looked fine, correct color and uniform from cylinder to cylinder. Fuel filter done at the same time.

I can be driving along with everything working fine for several hundred miles then like a switch was thrown it feels like I've lost 20 or 30 lb-ft of torque in that 2500-3000 rpm range. No gradual degradation of power.

Same here full throttle and 3/4 fine but 1/4 or 1/2 the x is reluctant to downshift and unresponsive. 2 things left air filter and cleaning injector . ( or plugged cats) ohhhh i forgot to say thAt i replaced the MAF .

Just want to make sure it s not your throttle memory. Drive your x in manual mode put it on 2nd aroud 2500 3000 rpm and smash the gaz pedal ( do this when you feel your x looses some torque) . If the acceleration is << strong >> ( blast off ) then your x is fine

Have you done anything? Man change tge maf And you will be fine . Your x will be alive again

Nope, haven't had a chance to do anything. Been traveling for work so the X5's been sitting in my garage. Thanks for the thoughts