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Need Help!!! Truck stalls when stopping

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Old 10-17-2011, 08:04 AM   #1
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Default Need Help!!! Truck stalls when stopping

My friends 2007 F-150 (4.6l engine)(77,000 miles) was shaking while at idle and the engine light was on. I changed the spark plugs yesterday and it fixed the shaking. We took it for a test drive and everything felt great. When we pulled back into my driveway the RPM's dropped down to about 200 and it stalled. Started it back up and the engine light was back on. We took it back out for another drive and found that every time we came to a stop the RPM's would drop down below 500 and it felt like it could stall. After we would come to a full stop the RPM's would stay constant at 500. After driving it around for a while it only stalled twice when coming to a stop and we probably stopped a hundred times. We took it to Salvo and got an engine scan and it said the #1 o2 sensor bank #1 was below normal.

Tried to diagnose the problem:
While the truck was running I unplugged each spark plug one by one and plugged them back in. Every time the engine would shake just as it did before then go back to normal after it was plugged back in.
I did remove the fuel rail on the passenger side of the engine so I made sure all of the connections were good. Everything seems to be good.

If the spark plugs were misfiring could that cause the o2 sensor to fail? Or should I assume that since the truck never stalled before I changed the plugs that it is something that I did that is causing the low RPM's?
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Old 10-17-2011, 08:41 AM   #2
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Need to check the codes......

If you puilled the fuel rail.. Im betting the orings were damange on the injectors....

Also .. In any of that process did you unplug the battery?

If you unplugged the battery .. you need to do the relearn process

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Old 10-17-2011, 12:19 PM   #3
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You probably need to relearn again...

unplug you battery again and and let the truck sit for a bit.. then hook up battery again..

Start and idle for 1 min with A/C and Radio off...

Then Idle for 1 min with A/C on full and radio on.

Then drive the truck around for about 5-10 minutes and you should be fine..

Also i would pull the fuel rail again and double check everything. Like Bob said check the o rings.
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Old 10-17-2011, 01:22 PM   #4
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This issue has nothing to do with the plugs, went through the same deal with mine. Pull the throttle body off and clean it with TB cleaner and then do the same to the MAF sensor. Should perk it right up, not sure why but even just a small amount of gunk in the Tb leads to issues
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Old 10-17-2011, 07:22 PM   #5
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Maybe the IAC is sticking? Could pull it and clean it if the 4.6l has one. Had a similar problem with my older 01 with the 5.4, and cleaning the IAC fixed it.
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Old 10-25-2011, 10:29 AM   #6
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Check the hose that is attach. To your brake booster . If it's only happening when you hit brake. Good luck
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Old 10-25-2011, 11:41 AM   #7
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Change your fuel filter, mine did what you are talking about, and poof....gone!
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Old 10-26-2011, 07:55 AM   #8
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Thanks screw04, it was the TB. After cleaning out the TB and the MAF sensor the truck runs great. The engine light was still on so I had the code checked. It was the O2 sensor. Replaced it and the code went out.

No engine light and the truck runs better than ever!!!
Thanks for all the help!!!
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