ndoutdrs

I have a mis fire at idle and NO CHECK ENGINE LIGHT. I have sprayed carb cleaner around top of engine when it was cold to see if I had a vacuum leak and did not notice any difference in the rpm's. I have replaced all spark plugs and gaped them at .045 as my Chilton manual states. I am getting frustrated as there has been NO check engine light. Looking for suggestions or ideas on what to check next.

lewissa81

It could be any number of things. Since you changed the plugs, next I would run a couple tanks with Techron and clean the throttle body/ mass airflow sensor. If you have a scanner, I would monitor the O2 sensors and fuel trims to see if you're running rich or lean, and if the O2's are switching. If you're running rich, it could be a faulty coil or injector. If your running lean, you could have a clogged/faulty injector, or a vacuum leak you just couldn't find.
Of course with both rich and lean conditions, you could have one or more faulty O2's. They can get lazy over time, misreport data, and can just fail. Monitoring them and the fuel trims will also help you determine whether you should focus on one bank, or if both are effected. Good luck. Those misfires can be a pain to find. I'm sure there are other things that I'm forgetting too.

gDMJoe

HINT/TIP: You'll find posting in thesection more helpful/appropriate than General F150 Discussion posts.
.