Eu preciso esfregar o fogão de novo, porque ainda está sujo.

Yes. In Brazilian Portuguese, you can often omit eu because the verb form preciso already shows the subject is I.

So both of these are natural:

• Eu preciso esfregar o fogão de novo...
• Preciso esfregar o fogão de novo...

Including eu can add emphasis, clarity, or contrast.

Here, preciso is the first-person singular form of the verb precisar, meaning to need:

• eu preciso = I need

It is also true that preciso can be an adjective meaning precise / accurate, but that is a different use.

In this sentence, it is clearly the verb:

• Eu preciso esfregar... = I need to scrub...

Because after precisar when you mean need to do something, Portuguese normally uses an infinitive:

• preciso esfregar = I need to scrub
• preciso estudar = I need to study
• preciso sair = I need to leave

So the pattern is:

• precisar + infinitive

Yes. Precisar can be used in two common ways:

1. precisar + infinitive
   when followed by an action

   • Preciso esfregar o fogão.
   • I need to scrub the stove.

2. precisar de + noun/pronoun
   when followed by a thing

   • Preciso de água.
   • I need water.

So in your sentence, de is not used because the next word is a verb: esfregar.

These verbs overlap, but they are not exactly the same.

• esfregar = to scrub / to rub
  • focuses on the physical rubbing action
• limpar = to clean
  • more general
• lavar = to wash
  • usually with water, soap, etc.

So:

• Preciso esfregar o fogão suggests the stove is dirty enough that it needs scrubbing.
• Preciso limpar o fogão is more general: I need to clean the stove.

Portuguese uses definite articles more often than English.

So where English says:

• I need to scrub the stove

Portuguese naturally says:

• preciso esfregar o fogão

Using o is completely normal here. In many situations, leaving it out would sound unnatural.

Fogão is pronounced roughly like fo-GOWN, but with a nasal ending.

A few pronunciation notes:

• fo sounds like foh
• the stressed syllable is the last one: -gão
• ão is a very common Portuguese nasal sound

A rough approximation for English speakers is:

• foh-GOWN
  but with the ending made nasal, not fully like English gown

Here de novo means again.

• esfregar o fogão de novo = scrub the stove again

Yes, de novo and novamente can often mean the same thing:

• Vou tentar de novo.
• Vou tentar novamente.
• both = I’m going to try again.

In everyday Brazilian Portuguese, de novo is usually more common and more conversational.

Also, de novo can sometimes sound like anew / from the beginning, depending on context, but in this sentence the natural meaning is simply again.

Portuguese has several forms that look similar, and this is a very common learner question.

Here you use porque because it means because and introduces an explanation:

• ..., porque ainda está sujo.
• ..., because it’s still dirty.

Very roughly:

• porque = because
• por que = why / for which reason
• por quê = why at the end of a phrase
• porquê = the reason (a noun)

So this sentence needs porque.

Here ainda means still:

• ainda está sujo = it is still dirty

It shows that the stove remains dirty even after something was already done or expected to fix it.

You will often see ainda used this way:

• Ainda estou cansado. = I’m still tired.
• Ela ainda não chegou. = She still hasn’t arrived / She hasn’t arrived yet.

Because estar is normally used for a temporary condition or state, while ser is used more for essential characteristics, identity, or general description.

Here, being dirty is a temporary condition:

• o fogão está sujo = the stove is dirty right now

If you said é sujo, it could suggest something more like it is a dirty thing by nature or it is generally unclean, which is not the intended idea here.

So está sujo is the natural choice.

Because sujo agrees with fogão, which is a masculine singular noun.

• o fogão → masculine singular
• therefore sujo → masculine singular

Compare:

• o fogão está sujo
• a panela está suja

The adjective must match the noun in gender and number.

No. In the second clause, the subject is not eu. The implied subject is o fogão.

So the structure is:

• Eu preciso esfregar o fogão de novo
• porque [o fogão] ainda está sujo

Portuguese often leaves out a repeated subject when it is clear from context.

So está sujo means:

• the stove is still dirty

not

• I am still dirty

The comma separates the main statement from the explanatory clause:

• Eu preciso esfregar o fogão de novo, porque ainda está sujo.

In writing, a comma before porque is common when the second part gives an explanation. In shorter sentences, you may also see no comma:

• Eu preciso esfregar o fogão de novo porque ainda está sujo.

Both can appear, though the comma is very natural here.

Yes. That would also be very natural in Brazilian Portuguese:

• Eu tenho que esfregar o fogão de novo...

This also means I need to / I have to scrub the stove again.

Very roughly:

• preciso = need to
• tenho que = have to / need to

In everyday speech, tenho que is extremely common. Preciso is also very common and sounds slightly more direct in expressing need.

Yes, it is completely natural.

It sounds like normal everyday Brazilian Portuguese:

• Eu preciso esfregar o fogão de novo, porque ainda está sujo.

A few equally natural variations would be:

• Preciso esfregar o fogão de novo, porque ainda está sujo.
• Tenho que esfregar o fogão de novo, porque ainda está sujo.
• Preciso limpar o fogão de novo, porque ainda está sujo.
  if you want clean instead of specifically scrub

So the original sentence is correct and idiomatic.