Check engine light problem
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Junior Member
Joined: Mar 2006
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Check engine light problem
My CE light on my 97 F150 4.6 4X4 Auto has been on for about 6 months. The truck runs fine. It does idle high when cold (seems higher than normal) but returns to normal when warmed up. When idling in park the engine surges (AC Off) from 800 to about 1200 rpm. I had the codes read and there are as follows: IAC overspeed error, Catalyst system efficiency below threshold, and system too lean.
I have checked the IAC sensor with an ohm meter, it is within range at 10ohms.
Anyone have any ideas??
I have checked the IAC sensor with an ohm meter, it is within range at 10ohms.
Anyone have any ideas??
Senior Member
Joined: Mar 2000
Posts: 481
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From: Westminster, CO
Originally Posted by lancasterkr
Anyone have any ideas??
https://www.f150online.com/forums/v8-engines-24/
Technical Article Contributor
Joined: May 2004
Posts: 6,509
Likes: 6
From: Georgia on my mind...
The IAC overspeed error is the PCM trying like hell to establish a stable idle, but it ain't working. Either that or you've played with the hard stop on the throttle body.
P0420 or 0430, catalyst effiency low usually means you've got a dead converter. If you can view your upstream and downstream O2 sensor switching rates, watch what the downstreams are doing. If they're switching lean-rich like the upstreams, the converter is dead. There may be a PCM calibration update to help allevate this code somewhat, but ultimately converter replacement is required to fix this. Big bucks at your friendly neighborhood Ford store. Best to go aftermarket, IMO, you'll probably spend $800-1000/ea for a catalytic converter from Ford.
System too lean, P0171 and/or P0174, start looking for vacuum leaks. This may be related to your IAC code, since an outside air source will cause an erratic idle and lean the engine out. If you've got access to a scan tool where you can view PIDs, check your BARO reading. It should be around 150ish Hz at sea level. If you've got one of those two letter cotton/oil gauze million mile air filters, be advised that oil and dirt from this filter can contaminate the mass air sensor and skew your BARO readings, this will make the truck run leaner than it should. Check your PCV connections closely, make sure there's no leaking or broken PCV connections.
P0420 or 0430, catalyst effiency low usually means you've got a dead converter. If you can view your upstream and downstream O2 sensor switching rates, watch what the downstreams are doing. If they're switching lean-rich like the upstreams, the converter is dead. There may be a PCM calibration update to help allevate this code somewhat, but ultimately converter replacement is required to fix this. Big bucks at your friendly neighborhood Ford store. Best to go aftermarket, IMO, you'll probably spend $800-1000/ea for a catalytic converter from Ford.
System too lean, P0171 and/or P0174, start looking for vacuum leaks. This may be related to your IAC code, since an outside air source will cause an erratic idle and lean the engine out. If you've got access to a scan tool where you can view PIDs, check your BARO reading. It should be around 150ish Hz at sea level. If you've got one of those two letter cotton/oil gauze million mile air filters, be advised that oil and dirt from this filter can contaminate the mass air sensor and skew your BARO readings, this will make the truck run leaner than it should. Check your PCV connections closely, make sure there's no leaking or broken PCV connections.
Senior Member
Joined: Sep 2005
Posts: 822
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From: cleveland ohio
Originally Posted by lancasterkr
I am leaning toward that cat conv problem, yuk!
but since I saw your new here, Let me be the first to Welcome you in the Forum!
