Duces2you

I have a 2002 4.6L f150 and I have been having a problem with it's idle since I bought it 4 years ago.

I have done everything over again in terms of cleaning out the intakes, oil, fuel filter, air filter, sparkplugs, MAF, O2 sensors, fuel cleaner, vacuum lines and fuel cleaner. My truck is well taken car of but it just has this really screwy idle and it has like a very rough but slightly shake in the idle and motor every 4 to 6 seconds. Its not enough to act like it's gonna stall but it is noticeable if u are looking for it.

Also the rpm will go up like 25 maybe 50rpms when it does this little cough for maybe 2 seconds.


What the hell is that? It's driving me nuts! I've hose clamed ever line I could find think it's a vacuum leak. And again my truck well taken care of is there something I'm missing?

Tghkd1

Maybe need new coils?

Duces2you

No I replaced them already and it didn't help. Like I said the truck is well taken care of and otherwise act just fine it has a lot of pep and get up and go. But this little funky idle is driving me nuts and I think it's a underlining problem cause the fuel economy stays at like 12mpg when I should get 12mpg on long trips.

Trav-ler

Go to your owners manual and follow the instructions for a battery reset. First disconnect your battery and reconnect it then do the battery reset. This may solve your problem.

Duces2you

Bump**

Spanky666

Might be the fact that I just had a clogged cat converter leading me to suggest, maybe a cat or more than one cat is starting to get clogged. My truck idled IMMACULATELY. Revved in parked without missing a beat. I changed $800 in parts before I looked at the cats. And it turned out one of the cats was clogged. Started off like yours though, ended up parked in my driveway waiting for parts to get here. Still idles great and revs great, but the driving/reversing has gotten to the point of being un-drivable. Apparently clogged cats will cause erratic idles, as well as, a noticeable drop in fuel efficiency.

Since yours is only doing it every now and again, it may be a broken cat/shattered. Clogging and unclogging occasionally. Easy enough to climb under and bang on it with your hand/rubber mallet and listen for broken pieces.

Duces2you

I have figured out I may have a vacuum leak on the brakes. When I do hard breaking and then give it some gas it make a rattling sound like a diesel truck. Just for what it sounds like 4 quick bangs in a row. It does not do that unless I'm hard on the brakes.
Maybe that has something to do with it and if not I'm gonna see if my buddy can hook his reader and I can see how lean or rich the fuel ratio is.

Duces2you

How many miles did you have on the truck before you swapped out the cats?

Spanky666

230,000. But I'm not sure i would use that as the gauge because if you're burning more oil than i am it could get clogged faster. Or again, could have broken or melted ceramic causing a blockage etc

Duces2you

I'll look at the CATs how can u tell if it's clogged would it be hotter on one side of the CATs