gdeg12

My 2008 5.4l has a rough idle. The idle gets worse when the engine is fully warmed up. The idle is much worse in park and neutral. When in gear, it is barely noticeable. It almost feels like it is shuddering. There are absolutely no trouble codes in the system and other than the idle it runs fine. I just did a fresh oil change with synthetic oil and a motor craft oil filter. Just replaced the air filter and fuel filter too. Nothing seems to make a difference. Throttle body and maf sensor are clean. Maybe a new maf sensor? My mechanic just cut both cats off as they were clogged and reset PCM, but I did notice a bit of rough idle before he did this. Please help!

haha

Possibly intake not getting enough air at idle? Maybe a bad throttle position switch?

adanvjr

Clean out the MAF sensor and Throttle Body.
It may help.


I was once having the same problem and doing that cleaning helped a lot.
The throttle body wasn't even that dirty, but it was dragging the idle down.

Regulator

just out of curiosity, what is the engine size and mileage?

j.low

Have a good man look into your Cat converters. They cause all sorts of problems.
The voice of experience.

JimmyB1232

Try checking the connections to the COPs. Maybe even pull the COPs out and blow out any debris down in the cylinder and put some dielectric grease in the boot when putting them back in. If one of those connections is slightly loose it can cause the spark/current to arc and jump around causing the shudder you're experiencing. If you want to check the MAF just disconnect it and see what the idle does. If the idle improves when disconnected then your MAF is bad. If it gets worse and kills the engine then your MAF is still good. Are you noticing any misfires/shudders/hesitation or anything when under load, going up hill, or WOT?