Rough idle problem

[johndough]

Hi, lately the last few times I've driven my truck when I've started it up and it runs at 1800 rpms (somewhere in that area, its been cold here in virginia so im going to assume thats why it starts off like that to warm up) but my problem is whenever the rpms start to go down to normal idle after warming up, its a really rough idle and the truck will run 1000-800 rpms and keep going up and down between those numbers and it sounds like it wants to die but it won't so its struggling to stay on. How can I fix it? I plan on cleaning my IAC valve but what else could it be besides that?

 

[Jazzer]

How many miles are on your O2 sensor? Asking for a friend.

-Jazzer

 

[Cees Klumper]

Check for a vacuum leak, the idle can't handle those at all.

 

[johndough]

How many miles are on your O2 sensor? Asking for a friend.

-Jazzer

haven’t replaced it since i bought the truck in august of last year.

 

[Jazzer]

They only last 80-100k miles and can cause many symptoms such as the one you describe. There’s only one on the y-pipe, kind of hard to get to.

Cees Klumper’s advice to check for vacuum leaks is spot on, as these old trucks hoses get brittle. You can follow vacuum hoses with an unlit propane torch or carb cleaner spray to see if you get higher rpms which indicates a sucking leak.

-Jazzer