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Q: my 2000 f-150 5.4 v8 has a very rough idle on 2000 Ford F-150

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idle is always rough, this problem started as a result of
replacing the timing chains. Can this problem be a result
of improper timing between the two cams. Could this be the result of a vacum leak.Truck has approx. 220k miles
(2) Answers
(1) Comments
why did you have the chains replaced?? did one break??

I would start with a compression test first to check for valve damage.

Yes. a vaccuum leak will give you a rough idle. the chains out of time will give a multitude of issues.

Roy
The chains did not break, they were worn and making noise, there was no valve
damage. If the EGR is mounted directly behind the throttle body, I removed the
vac line that attaches to a diaphragm actuator on this part, put my finger on the
connector and felt no suction at all. Removing the vac line did not effect the idle.
Late reply, but the EGR will not have any vac during idle. You can test the EGR by connecting a small handheld vac pump to the EGR and pull vacuum. If your vehicle begins to die, then the EGR is working. I don't recall the specs of the amount of vac it takes, but it's not much. In fact, you can connect a hose to the EGR and suck in with your mouth as well. On my 98 F150 5.4, the IAC valve sits directly behind the throttle body. The EGR is to the right, connected to the EGR tube that connects to the driver side exhaust manifold.
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