Untrained

My 1998 F150 4.6 has a rough idle. It is worse when I first start it up. I have checked for a vacuum leak, cleaned the IAC, and replaced an Oxygen Sensor regarding a code that the truck had. I am very confused now, and this really bothers me. I am at a loss for what it could be at this point. It happens whether it is hot or cold.

Jbrew

Clean the MAF.

akdoggie

then clean the holes behind the butterflies on the throttle body also.

Untrained

I've cleaned the MAF, but this throttle body suggestion is new to me. What/where are these butterflies?

akdoggie

Pull the TB 4 bolts off and remove it. Clean the back side, behind the butterfly plate, Make sure the shaft isn't loose. A loose shaft can cause irregular idle due to vacuum loss at the shaft.

Untrained

Thanks for the suggestion, I'll try that when I get some time to do it. Also, do I have to get a new gasket for the TB to the manifold?

Jbrew

The TB doesn't connect to the manifold, so I would say no.

Untrained

Ah, I see. Thanks for the help, I'm still pretty new to these.

Jbrew

Permatex Ultra Black or you can get a paper gasket for the throttle body to TB elbow mating surface. For TB Elbow (plenum) to intake you can use a crush gasket or same, - PUB RTV..You can purchase some Ultra Black from just about anywhere, 3rd party auto supplier.

BareBonesXL

How many miles on the plugs? How did you "check" for a vacuum leak? Do you have a code reader or did you have it done?

If you have a code reader with live data capability it will tell you things, like if you have a vacuum leak.