I know this thread is dead but I am bringing it back. I will copy and past my thread from another forum. Seems similar but with a bit more detail:
Back in October of 2011 my stock battery finally died in my stock (except axle backs) 2005 Mustang GT. I replaced the battery with a Duralast Gold. After I closed the hood, I started the car and all was good. Shut it off and then 3 hours later got in to go out for dinner. Got out of my drive way and started to accelerate down the street and the car shut off, with a fail safe mode message. Turned it on and the MIL was activated. I drove to dinner and it was fine. After, I drove to my friends hours a few miles away to use his reader. Came back with P061B and P2106. Cleared it and he and I went out for a drive, two miles to the gas station. Filled up an then got on the highway and accelerated, immediate fail safe, P061B and P2106. Cleared it and drove it hard (trying to replicate conditions to find a common cause) for another 5 miles and it was fine.
Looked around forums and the web for those codes and found a lot of people reporting bad TPS or TB. I cleaned the TB and MAF and that did not work. I bought a 2007 TB and TPS (new style) and installed it. Over the next two months, my car fail safe'd several times while on the highway over 65mph. It seemed to do this after accelerating to those speeds although sometimes I would have constant throttle position and it would just go in to fail safe mode. Only common variable at this point was rain. It was always raining. I did/do have the dreaded water leak but it is almost completely fixed and now requires a driving rain for 4+ hours before I see a drop inside the car.
The car would see fail safe probably a dozen more times from December through the beginning of April. It would usually happen one time and then follow with a second or third time within 20-30 minutes.
In February, it fail safe'd and threw 12 codes:
P0446
P2106
P061B
P151A
P201
P202
P203
P204
P205
P206
P207
P208
This one time code frenzy and variation in codes led me to believe a bad ground was to blame for bad sensor readings. I made an 8ga engine ground kit and installed it to the negative terminal, PCM mount, passenger valve cover, throttlebody stud, driver's side valve cover, and the factory ground in front of the factory air box. After installing it, I reconnected the battery and started it up. Car sounded a little louder than it had earlier in the day and I was hoping to attribute it to stronger grounds/voltages. Pulled out on to the road and went WOT and in 100 yards it fail safe'd. Pulled in to a parking lot turned it on, no code. Turned it on, pulled on to the road and gave it a little throttle, fail safe. Pulled over, read P061B and P2106, cleared the code, started it up and drove, fail safe. Read P061B, P2106, and P0446, cleared, started up and drove home. Went out later that day to a closed strip mall and ran 6 1/4 WOT runs in their empty parking lot. No fail safe, felt strong. On this day, there was no rain and it was about 79* and sunny.
In running ScanTool, I read 13V+ at the ECM, and my fuel trims seem to vary from 0 to 30%. My dyno yesterday said I was running a rich 11.2 A/F at WOT. I am not sure what other parameters I should watch to see variance from normal that may explain my issue. BTW, all of my fail safes were shut offs, not limp mode.
Of the 20 or so times I have hit fail safe my car reports:
A MIL with P061B and P2106 75% of the time
A MIL with P061B, P2106, and P0446 50% of the time
A MIL with P061B, P2106, P0446, and P151A 25% of the time
A MIL with the 12 codes above, one time
The car is not tuned and has the factory tune. I do not have anything on the car other than resonators and a ported and polished throttle body & JLT catch can (which were installed after the problems began). MIL is not always activated when it fail safes.
I know P446 is EVAP purge solenoid but it doesn't always come up and I haven't had any issues with starting or filling the car, which seem to be the identifiers for that issue.
I have not pulled the O2 sensors to check to see if they are dirty from running so rich. I have not seen any burnt wires or any burnt fuses. Sometimes the car feels a little sluggish (but still faster than my 05 V6) or has a noticeably quieter exhaust note.
Fuel filter was changed last September, oil in January, air filter is still clean (can't remember when it was changed last)
2007 Freestyle's and F150's have reported P061B and P2106 with a bad factory tune and the TSB has a new file. Haven't found such a TSB for my car.
Have also not found my situation or code combination in any web or forum searches.
Update April 25, 2012
So since the issue started when my battery died and I put a new one in, I decided to replace the 8 month old battery with an Optima Redtop. Previously, disconnecting and reconnecting the battery has caused a fail safe on the very next drive. Last night I put the new battery in and floored it and it did not fail safe. This morning, I pulled out on to my street, got on the throttle and it fail safed. I have ruled the battery out now and I got P061B and P2106 again but pending this time with no MIL on.
More than 50% of the fail safes have occurred after accelerating while over 50mph or while just cruising over 65mph.
So far I have replaced the TB TPS, and 2 batteries with no luck.
My car does not have a tune, intake or any mods other than the new TB (which was ported and polished and installed after the problem started) and MacBoomtube resonators. Everyone I have seen with this error has gotten it due to a tune… Well my car is still stock.
Any ideas are appreciated.