idle issues 2000 mountaineer

[cinomed]

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

 

[2000StreetRod]

Which engine?

I'm surprised you couldn't find help on the forum. My search of "P0171" resulted in 24 pages of related threads (30 per page). Here's a link to one of mine: Lean condition procedure which I need to update. You didn't post which engine you have but your symptoms are typical for the SOHC V6 leaking intake manifold gaskets. It is difficult to detect leaking intake manifold gaskets with carb cleaner, starting fluid, propane, etc. because the IAC valve will quickly compensate for the change if air/fuel ratio. A smoke test is the only reliable method.

The PCM commands the IAC valve to the desired idle speed. p1506 Idle Air Control Overspeed Error indicates that the engine speed exceeds the range of the IAC valve. That could be due to a bad valve but more often is due to unmetered air entering the intake manifold (leaks). This is supported by the two lean condition codes: P0171 and P0174. The gaskets dry out and shrink with age. They are inexpensive but take several hours to replace if you've never removed the upper intake manifold before. I suggest replacing the upper and lower intake manifold gaskets if you get to that point in my procedure.

Edit: Welcome to the forum!

 

[swshawaii]

Your plan of attack seems good, lean codes can be a PITA. Long shots here, have you checked the brake booster or PCV?

http://www.explorerforum.com/forums/showthread.php?t=313677

 

[cinomed]

I'm surprised you couldn't find help on the forum. My search of "P0171" resulted in 24 pages of related threads (30 per page). Here's a link to one of mine: Lean condition procedure which I need to update. You didn't post which engine you have but your symptoms are typical for the SOHC V6 leaking intake manifold gaskets. It is difficult to detect leaking intake manifold gaskets with carb cleaner, starting fluid, propane, etc. because the IAC valve will quickly compensate for the change if air/fuel ratio. A smoke test is the only reliable method.

The PCM commands the IAC valve to the desired idle speed. p1506 Idle Air Control Overspeed Error indicates that the engine speed exceeds the range of the IAC valve. That could be due to a bad valve but more often is due to unmetered air entering the intake manifold (leaks). This is supported by the two lean condition codes: P0171 and P0174. The gaskets dry out and shrink with age. They are inexpensive but take several hours to replace if you've never removed the upper intake manifold before. I suggest replacing the upper and lower intake manifold gaskets if you get to that point in my procedure.

Edit: Welcome to the forum!

it dose have the 4.0 v6 in it.the guy i got it from said he replaced the intake gasket 2 or 3 times but it didnt seem to change anything. sorry about this i didnt even think about doing a search for p0171 it had been a long couple days trying to figure this out. thanks for your input ill see about getting a smoke test done on it and see where that goes.

 

[cinomed]

Your plan of attack seems good, lean codes can be a PITA. Long shots here, have you checked the brake booster or PCV?

http://www.explorerforum.com/forums/showthread.php?t=313677

i have not checked the pcv and i did a vac leak test with the carb cleaner around the break boost, the breaks seem to be fine for the most part just going from say 40 to a stop it fights around 10mph. if im going slow to begin with it dose not do it. is there another way to check those parts?
thanks

 

[cinomed]

should i take a stab in the dark and do a fuel filter?