I have been dealing with rough idle for little while now. First it started in park and when I would be in reverse gear and stopped. Now when I’m driving and brake to stop when I stop the rpm’s drop to about 400. It’s a 07 flex fuel 5.3 lt with 200k. The plugs and wires were changed just last year. I have checked and checked for vac leaks can’t find any. Checked fuel pressure and it’s at 60 psi. And there are no check engine lights. Any help would be greatly appreciated.

 

Need a scan tool to see the fuel trims and where they are at.
There is no doing your own repairs without a quality scan tool nowadays.
Cleaning the throttle body is the only freebie guess I can give you.

 

Ok I think I have a scanner that will log the fuel trims but exactly which ones would I need? Also tried cleaning throttle body and maf sensor. But the help is appreciated

 

Short term fuel trims, STFT should normally cycle between -3 and +3 at idle.
MAF and MAP sensors can be at the edge of their range but not report a failure code. That's where the high-end scan tool comes into play.
I had a bad MAP in mine, and it was losing 3 mpg. No set hard codes but my scan tool has 2 MAP sensor tests built into it and one test erratically showed fail. I'm not one to swap parts but a new MAP got my MPG back to normal.