Ok, I know this issue has been beat to death and I am glad to see that I am not the only one with this issue. I have read about every thread in here about rough idle problems. I have a 2001 F150 w/4.6. I am hoping to find someone who is (or has) experienced this same thing and has found a solution, in that I am rapidly running out of money chasing this down. So far I have replaced the IAC, checked vacuum system, ran Lucas fuel system cleaner, replaced all plugs and COP's, tested PCV, had dealer reprogram PCM for the TSB on idle RPM's...and there has been no improvement what-so-ever. PCM is throwing no codes and another mechanic thinks it may be a bad PCM, but I don't think this is it...any insight would be greatly appreciated.

 

How many miles and when did the problem start? Only thing I see missing from your list of items is the induction service to clean the throttle body. Maybe try cleaning the MAF sensor?

 

Power balance, injector flow test, compression check, mode 6 data, fuel trims, baro, etc... will all help diag your concern. Hard to diag over the net but I'd start with compression, then injector flow, and so on.

 

I had power balance and compression checked at 2 different places. 1st place said all cylinders are firing, but #4 was low. Second place (the dealer) said #'s 2,4, and 7 were misfiring and #4 down 20%. Based on that, I replaced all COP's and plugs. Engine runs a bit smoother but still not a complete fix. I am now worried that #4 might have bent valve and I don't have the money for that.

ChrisT- I bought this truck used at 120,000 and previous owner said it had been an issue for awhile. I did clean the MAF with some store bought MAF cleaner.

 

Is it only a rough idle problem? Usually notice misfires more than just a rough idle. The BG or Motorvac induction cleaning (to remove carbon deposits) is around $130 and is well worth it. Stay away from that Lucas crap. Either use Chevron with Techron, Gumout with Regane or BG 44K fuel system cleaner. When was the last time your fuel filter was replaced? If it's been 15k miles or more, replace it. Is it a Ford dealer mechanic that thinks the PCM may be bad? I really don't think that's the issue. If you think cylinder 4 is the culprit, disconnect the COP and see if it still idles rough.

 

Had fuel system cleaned and fuel filter replaced today and no change

 

Hey check out your heater hose that comes out of the fire wall just above the #4 cylinder if it leaks even just a little it will misfire #4.

 

Sounds like the problem is pin pointed to a miss fire.
Just throwing this out there..... possibly injectors? Fuel system cleaner won't get rid of a faulty injector. You can have them tested or test them yourself. I believe they're resistance tested (ohm) I'm not sure exactly how on these trucks but it sounds pretty simple. Anyone else help with testing them?

 

Pull the fuel rail up and throw a few jars under the injectors to see the flow pattern of them, but the injectors are pretty good on these trucks. Don't recall replacing any injectors on 97-03's ever, now the newer trucks are a different story. Not saying it's not a possability but I doubt it. I've seen LOTS of these trucks run like crap with non motorcraft plugs and/or coils.

 

did you clean out the egr passage to the throttle bore

 

When I worked for Paxton, Ford had an Issue with a bad clamp on the heator hose. This would be located on the passanger side against the fire wall. If this is the issue you need to replace the coil pak that the hose was dripping on. Try squirting windex on only that port of the exhaust manifold to see if the temperature is the same on all cylinders. The compression on all cylinders should not be below 130 psi on any cylinder.

 

True but mode 6 would show the misfire on cyl 4 if that were the case.

 

Well, issue has been resolved...at a very high price. Did a compression test and #4 was reading 30 while others read 190. Figured out where this is going? Yup, bought me a brand new engine. Ordered a used one, but got a crate motor instead...the only good thing to happen.

 

how did you order a used one and get a new one.

 

Same way he had the compression checked twice before I guess, someone didn't know what they were doing.