2000 mercury mountaineer idle issue
 

hi guys i have a 2000 mountaineer that is having some idling issues. when i bought it it would rev to 2k rpms then drop to 500 and back up to 1500. so this is what ive done to trouble shoot the issue
1 had it scanned and came up with following error coded p1506 Idle Air Control Overspeed Error, P0171 system too lean bank 1. P0174 system too lean bank
2 checked for vac leaks with carb cleaner --nothing found
3 replaced iac valve seemed to help but not fix the issue
4 replaced tps sensor helped a bit more but still did not fix the issue
5 replaced maf sensor helped yet a bit more and still did not fix the issue

so the status now is that it starts revs to 2k rpm bottoms out at 500 then levels around 900 -1100 while in park and neutral and bounces between them. in drive and reverse it idles a steady 1100, but when i go down the road it runs fine no loss of power or anything, but when i come to a stop it will idle around 1500 until i come to a complete stop then drops to 1100. also when i break its fine till below 10mph then grabs and grinds a little. (i believe its cause its fighting the rpms to stop may not matter but thought id mention it). next step is spark plugs. i was gonna do a tune up and oil change since i just bought it just to be sure it has recently been done.

ps sorry if its been mentioned somewhere else i could not find it any help would be appreciated thanks in advance