Engine diagnostic tool

Hello,
New to the forum here and wanted to see if anyone could answer this for me.
If I got an engine diagnostic tool, would it tell me the problems my 4runner might have, if there is no check engine light?

 

If you know what your looking at it's possible. You should have an idea of what certain data PIDs lok like when the engine is running well, and there are no problems. The most obvious signs of a problem are the short and long term fuel trims, other data like o2 sensor and maf readings will affect fuel trim, so learn fuel trim. misfires can be felt, a failed temp sensor can have weird symptoms, and iac valve problems happen seemingly all of the sudden, but there are codes for such events. Fuel trim is a go to, learn what fuel is doing, expand diagnostic skills.

 

is there a specific problem you think might be happening or more just as a preventative maintenance tool to keep ahead of things as they happen?

 

if you're just looking for something to keep an eye on things I used to have the ultra guage on my Tacoma, worked pretty well and you could change the layout of each screen and decide on what gauges went where. You can check them out here: http://www.ultra-gauge.com/ultragauge/

I had in mounted like this but a lot of guys had them up by the rear view mirror and some had them off the pillar area