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Discussion Starter #1
I have a 1999 mustang V6 and its been putting out a P0455 code for a couple of months now. I would reset code by disconnecting batt and it would stay off for about a wk then return. The seal on my gas cap is good, I checked for vac leaks under the hood ect but everything seems to be intact. Other than the light coming on, the car ran fine. Recently the car has started to idle at low RPMs (feels and sounds like it wants to die) when coming to a stop OR when starting car up in morning. It feels like its misfiring a bit then it will stabilize and run fine. Yesterday the misfiring got so bad after leaving a store upon starting up that I went to auto zone and had CEL codes read. Now I'm putting out a P0300 (random misfire detected) code in addition to the same P0455 code. Can someone point me in the right direction. I had plugs, wires, and fuel filter changed about 4 years ago so I'm hoping this misfiring is related to the EVAP problem. Thanks
 

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I have a 1999 mustang V6 and its been putting out a P0455 code for a couple of months now. I would reset code by disconnecting batt and it would stay off for about a wk then return. The seal on my gas cap is good, I checked for vac leaks under the hood ect but everything seems to be intact. Other than the light coming on, the car ran fine. Recently the car has started to idle at low RPMs (feels and sounds like it wants to die) when coming to a stop OR when starting car up in morning. It feels like its misfiring a bit then it will stabilize and run fine. Yesterday the misfiring got so bad after leaving a store upon starting up that I went to auto zone and had CEL codes read. Now I'm putting out a P0300 (random misfire detected) code in addition to the same P0455 code. Can someone point me in the right direction. I had plugs, wires, and fuel filter changed about 4 years ago so I'm hoping this misfiring is related to the EVAP problem. Thanks
How many miles does your stang have? I'm hopeing for the best here, it doesn't sound good.
 

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Discussion Starter #3 (Edited)
It has 140k miles. Just an update. My car just died on me as I was exiting a freeway and coasting down the exit ramp. I've never had a car die while running. This seems like its something new going on here on top of the EVAP leak. It started fine this morning, engine ran smooth, no misfiring, no low RPMs at stops, it ran like it should then all or a sudden the steering wheel became hard to move and I press gas and see the engine died. I pulled over and it started right back up no problems. Could it be the IAC? How can I test this?
 

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3ntr0py said:
It has 140k miles. Just an update. My car just died on me as I was exiting a freeway and coasting down the exit ramp. I've never had a car die while running. This seems like its something new going on here on top of the EVAP leak. It started fine this morning, engine ran smooth, no misfiring, no low RPMs at stops, it ran like it should then all or a sudden the steering wheel became hard to move and I press gas and see the engine died. I pulled over and it started right back up no problems. Could it be the IAC? How can I test this?
Hmmm sounds like they engine is reading a code and turning off. Man i have no clue ive never heard of this.
 

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PCV valve is still strong spring back? EGR lines crack and leak alot. My number one suspicion is ignition. Wires not fully connected, one bad spark plug, plugs not gaped correctly but maybe its time to replace the ignition coil. You can use an Ohm meter and look for consistent resistance one to another. AM sells our ign. coils.
 

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Discussion Starter #6
Just an update. I removed my IAC and cleaned it out good. It was quite dirty. I also cleaned my throttle body out with a toothbrush, it had a lot of carbon build up. This seems to have made a difference and my car hasn't die on me while driving again but I'm still noticing that when I start my car up after its been warmed up (say I drive to the store then come back out and start it) that it has a very rough idle. Sometimes it is rough enough to set off a p0300 code (random misfires). After it does about 30 seconds of rough dancing it will stabilize and idle fine. On cold starts it runs and idles perfectly from the get go.
WHAT I'VE DONE THUS FAR:
-cleaned out IAC and throttle body, MAF also
-checked all vac lines with carb cleaner while running, nothing found
-PCV valve is rattling and providing a good vacuum.
-checked grounds
-tested resistance on all spark plug wires. All were within limits but I'm still going to replace them.

Should I take of my EGR off and check it? What else can I try here?
 

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I don't believe the EGR will cause any misfires unless you're recycling pure liquid fuel in such an amount to cause puddling inside the chamber which is almost next to impossible. All the EGR does is recycle gas fumes from your exhaust back into your intake to be burnt, thus reducing emissions. This sounds like a spark plug problem to me. When is the last time you checked them out? I would pull all the plugs and check the gap on them. I good gap will be about .055" for a N/A engine. Anything above .065" would maybe explain the misfiring. Platnium plugs are "good" till about 100K miles, but i've seen them fail way sooner at like 60K. You can easily replace your spark plugs for about $15 if it's been a while. Also, are you still getting the P0455 code?
 

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Im no expert but try replacing the spark plugs thats the first thing that comes to mind when i first read this
 

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Discussion Starter #9
Yes I am still getting the p0455 code. I cleared the CEL about 5 days ago and it just popped back up. i'm beginning to think this stalling issue is the IAC and not related to my EVAP leak. I cleaned the IAC good but I'm still getting rough idling after starting my car with a warm engine. I hear my CAI gasping for air while its idling rough. If I unhook the connector from the IAC while engine is running the RPMs drop like they should and the car doesn't stall out but when I hook it back up I can hear the same gasps for air from my K&N filter. Is there anyway to test the IAC before I buy a new one?
 

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I copied this from another forum for you. They guy ended up having the grommet by his filler neck crack so maybe this can help....

Absolute first thing. Check the gas cap.

Next check the grommet sealing the filler neck to gas tank seal. As these cars age, the grommet cracks and leaks. Gas is hard on rubber parts. Typically this results in a gas leak as the car is filled.

Then inspect the gas filler neck itself. Esp under the plastic "guard". Sometimes water/salt will collect under the plastic and rust out the filler neck.

Next check the vapor lines in the engine bay. Follow the EVAP vapor line from the rear TB area back under the right hand fender well. Look under the car for damage.

Pay special attention around the gas tank and by the charcoal canister. Inspect the lines looking for disconnected or damage. The charcoal canister is located next the gas tank behind the left wheel.

The P0455 indicates a LARGE leak so we are not looking for pin point holes here. This is further back up by the fact you can SMELL gas. If you still can't find it, look around. Use your nose. Has anything else changed?

---------- Post added at 04:26 PM ---------- Previous post was at 04:19 PM ----------

are the IAC for the 94-98 the same as the 99-04? I might have an extra for ya. Where do you live too?
 

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Discussion Starter #11
Thanks stallion Im gonna start doing those recommendations right now!!! And I do smell gas at times. I'll take pics and post.
 
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