04 XF 6spd 159,000
Owned for 2 weeks now running great
replaced the air filters, changed oil and filter , flushed the coolant with all new, replaced the throttle position sensor Pedal, the throttle position sensor on back of engine, replaced the MAP sensor ( Bosch) the crank shaft position sensor, (Bosch) i have done the reset several times with the key and holding down the pedal.

So today driving to work it started up again. And so did the reset and once again running fine. And no check engine light at all.. so I am lost. Please any advice be great.

 

I'd put an OBD reader on it in the "real time mode" and watch fuel trim, advance, etc. and see what changes when it acts up - over what the readings are when it's running well.
There are no codes because nothing is going far enough out of expected parameters to trigger a DTC. But you can be SURE, SOMETHING will show up on a sensor SOMEWHERE that will give you a clue as to what is not right here.

Just be careful, say you see some O2 readings that are "way out" when the car acts up - DO NOT just change the O2 sensor(s) that are reporting odd numbers. CONSIDER that the sensor in question is NOT lying, but is reporting something it really sees. THEN try to logically determine what is REALLY doing on.

I had a funny thing with my Ford Ranger, it would loose power, it could idle, but not pull at all - did this a few times. Took me a month, it was the MAF/IAT sensor, it was lying to the ECM. Found it by:

Keeping an eye on fuel pressure - it was OK.
Watching a lot of readings in real time mode - saw some odd things with the stuff coming from the MAF/IAT. "Cleaned" the MAF like some told me to, ended up changing it - problem solved.

It took a little detective work and patience, but I found it!

 

ok so when you say real time what does that mean. Thank you for the help.

 

Most think of an ODB reader as "that thing you plug in to read the codes".

Well, most do WAY more than that. In the BOSCH 1100 series, you select "View Data" - this takes you to screens that show what EVERY sensor in the powertrain system is telling the ECU.
You can watch O2 level, throttle position, ignition timing advance, fuel trim, system voltage (as seen by the ECM, not battery voltage), engine RPM, ambient temperature, intake temperature, volume of air flowing into the engine, DOZENS of sensor readings the ECM is using to run the engine. In essence, you can know what the ECM knows - and if a sensor is lying, you will see it. (Ok, actually, timing advance is what the ECU is TELLING the timing to be - if THAT is way off, other sensors are lying to the ECM and making it make bad decisions... But MOST readings are what the sensors are telling the ECM and the ECM is using that information to try to run the engine.)

For Example:
If ambient temperature reads 172F but it's only 65F outside, you know THAT sensor is lying.
If intake temperature reads -12F, but it is 65F outside, you know the IAT sensor is lying.... etc.

If your knowledge of such systems in modern cars is sufficient, you can figure out what is going on.
If your knowledge is marginal, as mine often is, you can google anything and eventually figure out what is going on. (It will be slow going, but you will learn SO MUCH!)
If your knowledge of cars is "I put the key in and it better start"; I'd not waste my time - take the car to a trusted shop with Mercedes experience, leave them a blank check, and hope they are honest as well as capable.
......... or take the car to a dealer and get ripped off shamelessly.

In any event, you have no code or "check engine light", this tells me you have something that is not out of line enough to trigger a code OR you have something happening that IS way out, but is of nature that the ECU can't determine there is something wrong. This does not mean it is impossible to find or fix, it just means it is something that is not easily recognized by the routines in the ECU.

 

One more thing, fuel pressure is NOT measured in our cars. The ECU assumes you have about 55psi at all times and runs the injectors based on that pressure. If your pressure is low, the ECM won't know that.
Fuel pumps and fuel pressure regulators can become intermittent and erratic. Fuel trim values and O2 values will be out of whack but maybe not enough to set a code.

The only way to know is to test or even full-time monitor fuel pressure. If you can catch it when the engine is not running right, check fuel pressure, if it is not within a few pounds of 55psi, FIX THAT!

I like this kit, it is almost as easy to measure fuel pressure as tire pressure (tho fuel pressure is a potentially dangerous thing to measure, as fuel at 50 psi will spray if you are not careful!):
https://www.summitracing.com/parts/otc-5630

 

Ok so when I first got the car 10 codes one of them was the following for an O2 sensor. I have not replaced those yet due to i do still need to replace wires and plugs., and fuel filter. So maybe once I get these replaced it will be better. Maybe not sure 🤔