Rough Idle But No Misfires

[EViS]

I have a 2004 Ford F150 which as of recently is idling rough (both on petrol and LPG). I have purchased a OBDLink MX and connected this to the latest version of FORScan.

I have added misfire PID's for all cylinders as well as short and long fuel trims for both banks and O2 sensor voltages. FORScan is not showing any misfires, fuel trims seem to hover at around 10% and all four O2 sensors show a voltage of between 4 and 7v.

I am new to diagnostics so looking for some guidance on how to proceed. I am a little at a loss as to what to test, and how to read the graphs to figure out what is causing the rough idle. Why would no misfires show up?

I do have a SuperChips programmer, should I remove this to get the truck back to stock, or will this not affect FORScan?

[FORScan]

As experience shows, this kind of problems (rough idle, periodical misfires etc) are hard to find just with help of computer diagnostic. On-board monitoring system fires DTC only when the misfire is too significant (cylinder almost not working). So if you for example have 1 misfire on 20 strokes because of ignition energy leak somewhere, we don't know a way to find the problem using FORScan.

[EViS]

Could a failing catalytic converter on one bank cause a rough and surging idle?

[FORScan]

Could a failing catalytic converter on one bank cause a rough and surging idle?

We think if engine works ok under load and the only problem is at idle, it is quite not likely the problem is in the catalytic converter. The only problem the converter may create (in our understanding) is a cramped exhaust, but it would be noticeable in power mode much more than at idle.

Most popular reasons of bad idle are intake vacuum leak and ignition power leak.

[thanhnguyen123]

only Ford IDS u can see balance test show u which cylinder misfire neither Mod 6 which i am remember ,if u have engine 4.6L i think 99.99 % is u have burned exhaust valve and depend how bad 1 or more valve burned.. do u have any codes storage in PCM such as: P0300 OR 01,02,03,04,05, OR P0306 ... ???? OR ANY CODES SHOW SHOW FUEL TRIM BANK 1 OR HAVE LEAK ...
BN