Stumble, Misfire, Rough running

[Mjasinski]

OK everyone I have turned to you for help….

First off the info on the car, it’s a 2003 ZTS, Zetec, ATX

Second…The problem:
The car seems to idle a little rough but I didn’t think much if it, but when you hit the gas real sudden the car falls on its face…almost like its missing, but it only does this for a second them slowly gets going again. It also seems to stumble on the highway while you’re maintaining speed at about half throttle...but very intermittently, seems to be no rhyme or reason to it that i gave found.

I’ve also had the car started missing while I was on a freeway off ramp under load...MIL blinking and all..its set a cylinder 4 misfire code, but I have only seen that once.

The Plugs and wires are relatively new, within 9000 miles. The car only has somewhere around 63000. So I don’t think its those and I looked at the wire and see no signs of arcing. But I have not tested the coil pack or swap with a known good one off of one of my other cars.

To try and fix this I replace with brand new parts, EGR valve and the DPFE. I found several things around blaming these symptoms on those…but no dice

A couple other interesting things I’ve noticed….i was thinking it could be a MAFS problem so I unplugged it to see if my symptoms went away, since I know the car is suppose to be able to run with it unplugged. But it would not even start…it cranked but never ran…

I also have this as a constant code: P0456 - EVAP Control System Leak Detected (Very Small Leak)…but I don’t think that’s related…but I could be wrong

Sorry this got so long, Thanks for any help you can give me!

[locdowg7]

First problem the stumbling idle. I would look to the IAC. They tend to get weak after time and especially with carbon they can and will stick. A semi good test for the tools you have would be to put it in neutral bring the RPMs up to bout 4000 for a few seconds then quickly let off the throttle. The IAC should catch the motor and keep it from stumbling or stalling out if it dosent then your problem is the IAC.

The missfire is just that a miss. If its not doing it now then dont stress.

The Evap code isnt really a big deal performace wise. You can check the gas cap for a cracked ruber seal but if thats not the problem then your most likely not gonna be able to diag that without a specialised fog tool. Try disconnecting the negative side of the battery and seeing if the code comes back.

[Mjasinski]

i don't care about the evap code, i know its not gonna hurt it i just thought incase it was important

how else would i test the IAC i have access to a Snap on modus and verus...

[locdowg7]

Access the dataloger pull up rpm and IAC and if it has a command function (been a while sence Ive used a Modus) cycle the IAC up to 100%. Then release the command function this should allow the computer to take back over and bring the idle back down If the vehicle stumbles or stalls you have a bad IAC. Somtimes you see the vehicles computer try to bring the idle up using the IAC after it stumbles with little or sometimes late response due to a weak IAC.

[G-forces]

Air leaks can cause that kind of symptom. Try spraying MAF cleaner around by the EGR valve and around the tube at the back of the IM, to see if you can find one.

[ZxProblemChild]

Originally Posted by locdowg7

First problem the stumbling idle. I would look to the IAC. They tend to get weak after time and especially with carbon they can and will stick. A semi good test for the tools you have would be to put it in neutral bring the RPMs up to bout 4000 for a few seconds then quickly let off the throttle. The IAC should catch the motor and keep it from stumbling or stalling out if it dosent then your problem is the IAC.

The missfire is just that a miss. If its not doing it now then dont stress.

The Evap code isnt really a big deal performace wise. You can check the gas cap for a cracked ruber seal but if thats not the problem then your most likely not gonna be able to diag that without a specialised fog tool. Try disconnecting the negative side of the battery and seeing if the code comes back.

Sorry to burst your bubble, it would be the positive battery cable that needs to be removed in order to clear the dtc. Also if it is the IAC valve... with car warmed up, at idle, make sure all of your power accessories
(and a/c) are turned off. Now, simultainiously turn your heater fan to max, and headlights to bright. If the idle is affected, I would look further into the IAC.

If your obd detected a misfire, there is something there that needs attention. The computer may not notice it even tho there is a problem.

The evap canister... not sure off the top of my head.

[Lancer211]

Originally Posted by ZxProblemChild

Sorry to burst your bubble, it would be the positive battery cable that needs to be removed in order to clear the dtc. Also if it is the IAC valve... with car warmed up, at idle, make sure all of your power accessories
(and a/c) are turned off. Now, simultainiously turn your heater fan to max, and headlights to bright. If the idle is affected, I would look further into the IAC.

If your obd detected a misfire, there is something there that needs attention. The computer may not notice it even tho there is a problem.

The evap canister... not sure off the top of my head.

Um.... removing the negative or positive battery cable should have the exact same effect.

[Mjasinski]

i know it does not matter which cable

i pulled the plugs, autolites....errr

so i put in some motorcrafts and well see what happens, seems to run better

[Scorpion]

Originally Posted by ZxProblemChild

Sorry to burst your bubble, it would be the positive battery cable that needs to be removed in order to clear the dtc.

Wrong, the negative will do it as well, same effect.

And you do know that removing the positive cable first is quite dangerous, right?
Imagine the amps that are in that battery.
Now imagine, as you're undoing the positive terminal, that the tool, usually a wrench, touches some part of the vehicle body. Now imagine ALL those amps (often more than an arc welder produces) suddenly free to run straight through that tool.

At the very least, you get a very nasty spark. In the middle, the tool gets hot, and something melts. At worst, I guess the tool will explode, showering you with molten metal.

Here's a couple of read-ups for you. I suggest you do more reading before performing any work on any vehicle.

http://www.popularmechanics.com/auto...o/4213127.html

http://www.ehow.com/video_512_replace-car-battery.html

[G-forces]

^X2

Any way you interrupt the circuit will have the same effect, just that the negative pole bridging to a ground point = nothing happens... positive pole bridging to ground = bad sparks.