Deceleration rough idle

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Aug 5, 2013 | 12:17 PM

Gotanoldtruck

Thread Starter

Cross-Country

Joined: Aug 2009

Posts: 87

Likes: 2

From: Chicago

Deceleration rough idle

Ok, have been living with this problem for years. 2007 F150, 5.4 Flex. 120K miles. At normal speeds this truck runs great. From time to time when I drop from 60/40 down to a stop it idles like it is going to quit. It never quits. Here is what I have done to the truck so far:

New cam phasers at 70K
New plugs at 120K
New COPs at 120K
New fuel filter at 120K
New air cleaner at 120K

Things I have not done:
Cleaned TB
Replaced MAF. (I have cleaned it)
Measured oil pressure drop

Am no expert but engine is not getting enough air/fuel. Thanks for the tips. I can live with the problem but it is annoying

Aug 5, 2013 | 05:53 PM

FireMe

Elder User

Joined: Nov 2008

Posts: 668

Likes: 6

From: Northfield, MI

You need to clean the throttle body as this is the #1 cause for an erratic idle on these trucks. Even a thin layer of sludge has an effect on air flow and it eventually causes the PCM to reach its limits of compensation.

You may want to make sure you have the latest software in the PCM as well.

I fix several a month by cleaning the throttle body and updating the software, which also clears the keep-alive memory and lets the PCM relearn all of its idle settings.