I've cleared all my codes (getting 1 1 1 for KOEO, Continuous, and KOER) and I still have a slightly rough idle (stumbles). I am pretty certain I don't have any vacuum leaks.

I checked my timing chain slack using a breaker bar and watching the rotor. It turns out I have between 5 and 6 degrees of slack...is this enough to warrant a new timing set and could it be the cause of the idle problem? truck runs good when at higher rpms, but I'd like to get rid of this rough idle and stumbling that happens at lower rpms.

 

I wouldn,t think chain is causing idle problem. Does it stumble in or out of gear? Feel like an intermitant miss? Ya might try cleaning the throttle plate and remove the IAC and clean it with carb cleaner.

 

I doesn't feel as much like it is stumbling while in park, but I think it is cause I can see the engine do some shakes here and there, when in gear though at a stoplight (750rpm), you feel it more...it definately feels like a random miss (replaced the cap/wires/rotor/plugs/coil/egr/evp/evr/map/ect/act).

I've cleaned the IAC, but I thought the symptoms of a bad/diry IAC were idle surging/wandering and not stumbling?? could it cause this?--maybe its bad? Nothing happens to the idle when I unplug the connector to it--is that a bad thing?

I've cleaned the TB and plates well.

 

Definitely clean out the IAC (idle-air-control). It mounts onto the side of the throttle body. Use air-intake cleaner, NOT carb cleaner. Get it all cleaned out and shiny, it actually comes apart into two piece, take them apart and get it real clean. My engine was stumbling around at 500-600rpm and occasionaly stalling, cleaning the IAC out brought it back up to steady 700-800.

 

thanks for the suggestion. I did this and it was in bad shape a while ago, so I replaced it with a new motorcraft for $68...no difference.

 

Have you replaced your PCV valve? Those can get clogged up and effect air flow through the system. In addition, with the way the truck comes, the PCV returns into the back of the intake manifold, dumping all the gases onto the 8th cylinder. That will cause misfires (and in some cases broken rings/burnt pistons on the 8th cylinder). This thread talks about the problem and what you can do to fix it (just requires moving the return hose from the back of the intake onto the vaccum tree):

https://www.ford-trucks.com/forums/s...threadid=15232

So here is what I would do: read that thread so know what the deal is, and then replace just the PCV valve. If doing that fixes your idle problem, then I would change the routing of the return line which is mentioned in that thread. If it doesnt fix the problem, I would still reccomend moving the PCV return line at some point in the near future. I just had to tear down an engine because this PCV problem caused broken rings in the 8th cylinder.

Let us know.. I got several more ideas for you to try if the PCV doesnt fix it (or if you've already tried this)

 

Thanks siphor, I went through the whole thing as you mentioned...take a look at my gallery and you'll see what the original routing did to my #8 piston...which has been replaced and re-ringed.

Here's what else I have replaced...IAC, EGR, EVP, EVR, ECT, Air Charge Sensor, MAP, cap, rotor, wires, plugs, intake manifold gasket, checked for vacuum leaks. Compression is ok, nothing to write home about, but all between 130 - 160. The only thing I can think of is the timing chain, and since it has between 5 and 6 degrees of slack, I thought it made some sense...

What else ya got?

 

I thought your username looked familiar..

You were the guy who first to me about the PCV probem. Since then, I've been trying to set off that fire alarm to anyone I can who might have the same problem, so thanks again for that..

Anyways, back to your truck. Have you checked out your vaccum system? You say that the problem goes away at higher RPM's. The vaccum system serves the purpose of controlling the engine at idle, at high RPM there is no vaccum in the system.

Check for cracked hoses and whatnot. Those damn plastic hoses they use always get brittle and break, I finally got fed up with it and spent the money to buy all new hose on my bronco cause it got to the point where every time I worked on something I cracked another hose.

There is a vaccum diagram on the air filter box, follow that to make sure everything is hooked up right.

Also, there are electonic solenoids which hook up to the vaccum system (they sit on a bracket which attaches to the ignition coil). Take the hoses off of those and see if they are clogged with anything. May want to check the electrical connections to them as well.

Do you have the C6 transmission? If so, it has a vaccum diaphram which has a hose that runs up to a tee on the firewall. I would replace that diapram because if those flake out I've seen them effect idle performance. Additonally, I've seen them fail to the point where transmission fluid gets sucked into the vac system It's like a $5 part and is held in by a screw so its easy to replace, I'd replace it anyways and have the peace of mind knowing that you wont have it fail.

 

I have the E40D, so no vacuum on the tranny.

I have replaced the PCV when I did the whole PCV reroute thing.

Here's what I have done with the vacuum lines. I tried listening to the lines with a section of heater hose as a stethoscope...then I also tried the method of spraying them all with quickstart fluid to see if I hit a vacuum leak...both things gave me nothing. I also tried to block the TB off with a block of wood and it died immediatly. I have pulled off and tested the TAB and TAD solenoids and I have 19" of vacuum off the manifold and have driven around with the vacuum guage to ensure I don't have a plugged cat.

when you replaced your vacuum lines, where did you get the new plastic hoses from? I was thinking of replacing them with regular rubber hose, but didn't know if I should replace them with the plastic for some reason? I pulled some of them off and it doesn't seem like there is a lot of free flow through them, but then again they aren't the size of heater hose, so I don't know if that means anything.

 

Have you done a fuel injector test? You disconnect the injectors one at a time in a certain order and watch for an RPM drop, and obviously, if you disconnect one and the RPM doesnt change then you have a bad injector. If you want the full rundown I can pull the procedure out of this book I have.

Checked the fuel pressure? When idling, it should stay solid at some number around 40 psi.

 

Nope didn't do that yet. I did try testing the fuel pressure by watching it when the engine turned off and it held it's pressure for a about 5 minutes before it started going down very slowly...If you don't think that does the same thing, can you post the procedure?

 

The book is at home, I'll post the procedure later this evening.

Another thought..

While I still doubt that the timing chain would cause this problem, have you hooked a timing light up to it to watch the timing? A loose timing chain will cause your timing mark to wave back and forth slightly, but not a whole lot, just a degree or two. And even that isn't a problem (and i seriously doubt would be the cause of your idle problem), it just makes your gas mileage crappy.

 

Well, I went ahead and replaced the timing set and it was a good thing I did too. The book says if you have 1/2" defection in the chain you should replace it...mine was 3/4" at least and real sloppy. The new one is real tight. Big difference...solved my rough idle problem and I have more oomph with it now. I'm hoping my mileage goes up from 12 and now maybe I can pass the emissions test. I'm surprised the chain stretched that much in 100K, maybe the truck was heavily used...I bought it in July. Runs real nice now. thanks for all the help.

 

Heh, talk to us 4.0 SOHC owners about timing chain problems, since we have to deal with the cheap plastic tensioners we were graced with. Timing chains are supposed to last the life of the vehicle, but everything wears out eventually, and those stupid tensioners are what always fail...

 

I must say, this is the first time I heard of a timing chain causing rough idle... oh well, there is always something new to learn!

Glad to hear you solved your problem. I'm very picky about my idle as well, I don't blame you for going after this one..