01 Explorer with 08 SOHC motor, rough idle.

[1998Explodasport]

About 20k ago I replaced my motor with a motor from a 2008 Mustang that only had 11k on it. Since the motor swap and 20k later I have had a rough idle but other than that the truck runs great. I tried swapping and cleaning MAF sensors, swapping coil packs, fuel and air filter. There is no CEL and no pending codes. The wires are also a few months old but I may try another set. I pulled a few plugs today and they looked really good but I suppose they should with only 30k on them.

Anyone have any suggestions on what is causeing the rough idle? Intake gaskets are also new and fuel trims are right where they are supposed to be. I believe before I swapped motors I replaced all 02 sensors as well. I may try another PCM since I have an extra one at my shop but I think I am wasting my time with that.

 

[Johnny_Utah_hs]

Were the engines the same? Particularly the displacement? I am a newbie so someone correct me if I am wrong, but I thought the computer has a power curve programmed and I would be surprised if the two engines have the same power curve unless it is the same engine.

 

[ranger7ltr]

What is the status of the IAC? Vacuum hoses?

Congrats on the engine swap...Quite a number of folks here have done the same with great results...But just like with the original engine the IAC and any vacuum leaks will cause problems...Since you are not getting any error codes the vacuum leak, if any would be very small I would think...

Since you have checked the plugs and they are looking good I would start by cleaning the IAC valve and then hooking up a code scanner and see what the LTFT and STFT are...Especially if the LTFT are high at idle you would have a lean condition that the PCM is trying to compensate for and that MIGHT indicate unmetered air getting into the intake tract...

UPDATE...I just read your fuel trims are where they should be...What are the fuel trims reading? Curious to see what they are reading...

 

[moogvo]

I also have a 'stanger in my X. try cleaning the throttle plates.

 

[boominXplorer]

I have somewhat of the same issue with my 04, I am running an 07 Ranger engine though. The truck drives GREAT just the idle is slightly rough. Its not real shaky but just has this very light consistent fludder, not a jump like a missfire. I used all the original sensors from the 04 engine so its not the electronics. I think it has something to do with the cam profile. On the cams I have noticed there is a different profile after 2005. The 97-04 engines have 01 stamped on the cams and 05+ have 02 stamped on the cams.

 

[1998Explodasport]

Congrats on the engine swap...Quite a number of folks here have done the same with great results...But just like with the original engine the IAC and any vacuum leaks will cause problems...Since you are not getting any error codes the vacuum leak, if any would be very small I would think...

Since you have checked the plugs and they are looking good I would start by cleaning the IAC valve and then hooking up a code scanner and see what the LTFT and STFT are...Especially if the LTFT are high at idle you would have a lean condition that the PCM is trying to compensate for and that MIGHT indicate unmetered air getting into the intake tract...

UPDATE...I just read your fuel trims are where they should be...What are the fuel trims reading? Curious to see what they are reading...

LTFT last I checked which was yesterday were -1% on both banks. STFT stay around 0%.

 

[1998Explodasport]

Still the same problem however now it seems to be down on a little power mainly on the highway. I am starting to think I have a cat that is going bad. I replaced the crank pulley with a new one from Ford which i believe helped a little but i still have the rough idle. Also I tried different IACs I have had at my shop and one of them was a brand new one. I recheck many times for vac leaks and never seem to find anything. When I did the swap I replaced any hose that looked questionable.