Will google see "404 redirect to homepage" as doorway spam?

This is a SEO question that bother me for almost a week now, i have tried searching online for more specific case study, and nothing appear to be relevant. I merely find anything good from google nowaday!

What i want to know is how "404 redirection to homepage" and is this considered to be a doorway spam by google or not? Since you can have hundreds of URL that is no longer exist, and its URL can be with keyword. After you set it to redirect to homepage, the bot will see hundreds of URL and all it get is the same homepage over and over again. And there is no server 404 returned to bot in html header code. This might be the technical issues.

Any opinion or direction for me?

 

"Doorway spam" ...why?... there is no content there so how can it consider it as spam...... instead u r submitting a redirect and google understands that is a redirect 301 OK....and not a 200 OK page... 404 pages are usually not indexed because the status is 404 Error page...

 

Ya, i know it may sound crazy at first. But wait till you see this google guideline that i revisited today, and found this statement that user website "MUST" show the 404. No exception, no 301, no redirect, no alternative.

https://googlewebmastercentral.blogspot.my/2011/05/do-404s-hurt-my-site.html
"Q: Most of my 404s are for bizarro URLs that never existed on my site. What’s up with that? Where did they come from?
A: If Google finds a link somewhere on the web that points to a URL on your domain, it may try to crawl that link, whether any content actually exists there or not; and when it does, your server should return a 404 if there’s nothing there to find. "

Also google will keep a record of all 404 in your website, viewable at google webmaster tool, and i think they do "index" it.

 

I made this experiment few weeks ago, 404 redirection that drives traffic form no longer existing web pages, once affect my SEO in positive way, another in negative.

And the conclusion is simple - its all about users experience:

If your whole website and main page have similar content - for example all about cancer, visitors will find content at least partly related to what they were looking for and your SEO should gain value.

But if 404 redirects will drive for different content, you will hurt badly. Because your stats like bounce rate or user session will knock down very fast.

 

if you have error page 404, and aftet 5 second Passing to homepage is very good for seo.