with Ermac, It depends how close you are to the opponent as you use the teleport slam (Or another launcher).
If you hit:

2, 2, Tele slam.
Your close enough to the opponent to land a jump kick (U+4) and teleport punch straight after the jump kick.

Hitting the jump kick which requires you to jump forward makes things a little harder if dont know the timing. Try comobing off of different launchers

b+1, 2, f+1, dash, tele slam.
b+1, 1, 4, tele slam.
f+1, 1, 4, tele slam.
2, 2, tele slam.

You will get it in time, and once youve got it then you step up ermacs game considerably. Ermac is a good character to punish with, and has a great projectle game, which makes him one of my favourite characters to play.

A few good combos that i use, involving the jump kick which will give you something to practice with at least.

2,2 tele slam, NJK, Telepunch, dash, 2, 2, Tele push.
Can add the jump punch at the beginning of the combo, and add EX to Either Tele slam, or tele push, or both!

b+1, 2 , f+1 dash, tele slam, jump kick , tele punch, 2, 2, tele push.
Can also replace the tele push with x ray for massive damage.

Ermac and Scorpion have the same directional motion for their teleports, which is Down, Back. The best way I can think of to show someone the timing for a jump kick teleport punch is by actually having them select a different character--Kabal. (among others)

Once you have Kabal in practice mode, do his fireball (which can be performed in the air)--it's Back, Back, 1. Now, do a jump kick and before you hit the ground do an air fireball. This should be very difficult to connect. Now, instead of doing a jump kick and then an air fireball, do the following:

Jump in the air towards your opponent--right before hitting them with the jump kick, press back, back and then the kick button IMMEDIATELY followed by the 1 button.

So it will be like Back, Back + Kick then quickly pressing 1 as soon as the kick connects.

Using this method should make connecting a jump kick fireball with Kabal fairly easy.

Now understanding the timing of how quickly you need to input a followup to a jump kick, apply that with the teleport punches.

I explained it with Kabal, because it's easier to explain with back, back, and it will let you get the timing for connecting jump kick to followups. Hope that helps.

Great tip!

yes, thank you so much. its taking some practice to get used to, but i'm actually landing the combo about 8 out of 10 times now compared to like 2 out of 10

Excellent, glad that it helped

Yeah, I hate that ALL of his decent combos have to use the jump kick teleport to do anything worth while.