Why on my1997tahoe when you remove the oil filler cap truck will stall and lots of suction

Normal, maybe. Since they started putting the engine case vacuum in the air filter plenum. Yes it happens. Many different cars today will shut down soon if the oil cap is not on. It has to do with the Mass air flow sensor.

There is not suppose to be vacuum from the crankcase so having none with the oil cap removed is normal.

look for vacuum leak. if air goes into engine and the maf does not see it
look the seal at oil cap filler, look to intake vacuum and hoses
hope it helps

You don't add oil with the car running

You broke the vacuum for the crankcase evacuation
(PCV System)

If you have idle problems then they have to be diagnosed

This is typical of the BMW, the name for the part to be replaced is under many names from BMW it either called Oil drain back valve.Crankcase oil seperator or better yet they should stick to the name PVC vavle,When this valve rupture internally either two things happen you burn and smoke oil like crazy,or you get strong vacuum in the crankcase as you are experiencing. The valve is located under the intake toward the front of the engine to remove you will need to remove the throttle body,

High idle usually indicates a vacuum leak, you may have one of the smog hoses disconnected, that would also cause a suction at the filler cap because the engine is taking in air pretty fast. I have a 93 2.8l and it will run fast idle for a short time when starting it cold, I have learned that is because it is running rich at that time and the computer thins a rich condition with more air so it is not smoggy.

Unless your throttle linkage is hung up, it is vacuum leak.

The 2003 e-class doesn't have an oil dipstick. Engine oil level is gauged electronically. Park the vehicle on level ground and cycle through the display using the buttons on the steering wheel. One of the options there will assist with the correct oil level and let you know if it's ok, too much or too little. Do note that there is an oil filler tube with a cap but this is really for filling the oil as well as removal with a vacuum suction tool in the work shop. The cap doesn't have a dipstick at the end.

That is normal, when the oil cap is dropped the vacuum to the engine drops also cause the idle air valve to close due to lack of vacuum.

The engine breather pipe seems to be blocked.
It may also damage the oil seals.