2Tight

The new truck (02 4.6) seems to have an odd idle issue that feels like a slight miss or injector. It only does it while sitting in gear with my foot on the brake. Put it in neutral or park and it's fine. It shows no thrown codes, cleanest smog test I've ever seen, and runs absolutely perfect otherwise. It's really not that bad but something has to be causing it. Is there anything transmission related that can cause this? Motor mount? Harmonic balancer?

Thanks for any advice or things to check for.

Edit: In a search I found it's pretty common with the 4.6 and not much can be done about it short of changing the cam profile.

Dsav

dude mines doing the same thing and im totally lost, its starting to **** me off, sorry i cant help ya, but i need help to! and it seems like mines worse in the cold

kaboom10

Sounds like a coil is on its way out. They short but don't fail and don't throw a code. Look for a vacuum leak next. Start with the PCV line. Oh clean the MAF with MAF cleaner to. If it's dirty it can do all sorts of strange things.

2Tight

Thanks for the input. Wouldn't a failing coil cause the same miss in neutral/park rather than in gear with a foot on the brake and be much worse under load? I've checked for vac leaks and it was fine. I will look into that MAF cleaning though, the previous owner had just serviced the K & N filter before I bought it and maybe he got overzealous with the oil. I've read up a bit on the problem elsewhere and there's several owners that have had the same glitchy idle 'in gear only' since their vehicles were new. A Ford tech said the cam profile is a bit aggressive on the 4.6L for more low end torque and it can show up in the idle.

kaboom10

When u put it in gear u are loading the engine. Yep a bit much oil winds up on the MAF and it gets confused.

Leebizkit

Mine is doin the same thing i got a 06 witha 4.6 clean intake and MAF no vacum leaks and good throttle position sensor which is what the dealer said was the problem...cant figure it out either my idle real low in gear and dies when i hit the brakes turn the wheel fast or turn on the a/c...if yall got any ideas let me know to

Leebizkit

hey yall mine was doin the same thing and i got it fixed... i took it to the ford dealership(first mistake) they charged me out the ***...but got it fixed none the less...they started with changing out the spark plugs, then they decarbed the throttle body and the heads and valves and cleaned out the fuel injectors, then they put a new fuel fillter and retuned the ecu and now it runs like new it cost me around 600 to get it done but after all was said and done it took like 7 hours and a day off work but it was well worth it to get my truck to quit dying in busy intersections and it runs like its brand new....hope this helps yall out

2Tight

Glad you got your problem resolved. The rough idle I posted on is not as severe as yours was for sure and is more of a nuisance issue for me. Mine doesn't effect the truck other than sitting at a light with a foot on the brake. I'm still waiting to clean the MAF and have the injectors serviced at Witchhunter when the truck can be down for a week.

ken.norwich

mine is also doing the same thing as all of yours. i have a 97 4.2L though. but i was leaning towards tps. my iac test fine and no engine codes are being thrown. could this be a possible bad ground?

Bell Blue Raider

my 99 4.6 does the same thing, but it's kind of odd. it only does it at night, if it does it during the day time then all i do is check cylinders 3 and 4 for antifreeze and check the coolant hose over cylinder 4 and try to see if it's loose and that fixes it during the day time. the same fix doesn't work at night though so i'm starting to think my truck is just afraid of the dark.... i'm going to check my passenger side plugs here soon and also trying to change my exhaust manifold so hopefully that's the problem with mine