About a week ago, my '03 Edge (3.0 standard fuel) started giving me some rough idling at startup, even with RPMs showing in their normal range for that cold start, so some misfires at 1000 RPM. The rough idle goes away after a couple minutes, and then the truck drives fine until it sits for a couple hours and cools down, and then the problem reappears. Finally, it threw an engine code the other day: the dynamic duo of P0301 & P0316 (Cylinder 1 misfire & misfires at startup) that many of you have seen throughout the life of this forum. This made me laugh, because it was a "no ****, Sherlock!" moment.

I'd gone back and read several preivous threads about this issue, and there was always various culprits and umpteen possible causes. Using those threads as a guide, here's what I've already tried/eliminated:

• Dumped a can of SeaFoam in it and have replaced the gas.
• OBDII scanner suggests my MAF is working fine, as its intake reading was spiking right along with the accelerator.
• Tested for vaccum leak by unplugging IAC valve. Truck shut off pretty quick instead of RPMs staying constant.
  • There are a couple of vaccum hoses that are showing some signs of wear, but removing them and plugging the hole did nothing. This was especially true for the one that leads from immediately behind IAC to the brake booster.
• I tried the "prime the fuel pump" trick by turning the ignition to on for a few seconds, then off, repeating several times before cranking.
• Plugs & wires have been in a couple three years, but are only 20-30k miles old (I don't put the miles on it that I used to before kids: 166k and its an '03)
• IAC valve was replaced 2 years ago, due to old one causing constant 3000RPMs
• Fuel filter was replaced between 3 & 4 years ago, again not a huge amount of miles on it.
• Oil pressure sensor was replaced about a year ago.

Of course, this still leaves me plenty of possible issues:
- PCV valve hasn't been replaced in some time... Will likely replace this no matter what.
- IAC valve is going bad... had bought cheap after-market valve.
- Coil pack could be getting weak - its the original, factory one.
- EGR valve (but its not throwing EGR code)

Are there any other possible causes I should look into that I'm missing? Any other tips on how to narrow things down? My gut insinct is telling me to change the IAC valve again, but I can't be 100% Especially if there was a way I could check the coil pack easily, or put a multimeter to something.

There is a potentially related issue that COULD help. There's been a few times - very sporadic and intermitently - where if I put my truck in gear right after cranking it cold, the engine will stall out. If I wait for the intial RPM spike at ignition to start drifting down, it doesn't do it. This is one reason I have that voice in my head screaming about the aftermarket IAC valve I had put on, but its also 17 year old truck with 160k miles on it.

Thanks in advance for the advice!

 

It sounds temperature related so I would question the sensors that are related to that. Intake air temp sensor, Temp sensor and or Temp sender(for gauge). You didn't mention O2 sensors or your vehicle mileage. O2's do wear out.

 

Thanks. I'll try to diagnose those as well. You're right in that I have not replaced O2 sensors, but I did not see any glaring faults when I was looking at the live data from my scanner, but I was not specifically looking at those.

 

If it were me ide focus on cylinder 1. Front passenger cylinder. Needs 3 things. Spark, fuel, compression. Test when it would normally misfire. Ohm out the injector, spark tester, noid light... then compression

 

Based on the advice of a friend of mine, I removed the throttle body and cleaned it, as well as the IAC valve. The throttle body had never been cleaned, so was indeed dirty, but that had no effect. IAC was relatively clean.

Based on the tip about the O2 sensor, I hooked up the scanner to check that more closely. I noticed that one of my O2 sensors had a relatively constant voltage, and others had varying. I admit to not knowing much about them, but would I be correct in guessing that both sensors on bank 1 should be doing the same thing (I recorded this linked video of the live data while idling, then in gear without much throttle- savedd as mp4 on Google Drive).

I'm on the verge of replacing the after market IAC valve, but am now wondering if there isn't an O2 sensor issue.

Also looking at replacing plug wires and plugs just to be sure, if necessary.

 

I have done more research into the O2 sensors, and constant voltage on the downstream is perfectly normal (Bank 1, Sensor 2). The upstream sensors were both varying voltage and were fine (Bank 1 Sensor 1, Bank 2 Sensor 1). This would seem to eliminate O2 sensors as being the underlying issue.

I am happy to say that it did not idle NEARLY as roughly this morning, although I gave it a couple extra minutes before putting it in reverse to back out of my driveway. I did plug up my OBD2 scanner when I got to work and erased the code, and we'll see what its like later this afternoon when I leave work & see if the codes come back. Perhaps it ended up being a sticky throttle body / IAC valve, and using the throttle body cleaner on the both of them solved the issues. Time will tell.

 

Based on continuing advice from friends of mine (although the responses here seem to have dropped off), I pulled the spark plug from cylinder one, since that was the one giving the code. I found the gap to be around .053. If you're reading this, you probably already know that factory specs are the gap should be .042 - .046, and too wide of a gap can causes misfires. When I put these plugs in, I had made sure they were all correct, but electrodes can wear over time. I had originally eliminated this possibility since the spark plugs were less than 50,000 miles old, it was at least worth looking to check, and I'm glad I did. Always the simplest things, right?

I re-gapped the plug properly and will see if the problem comes back right away (or if a different cylinder causes the problem). If not, then I'll throw new plugs and wires onto it next weekend.

 

To follow up on my earlier update, cleaning & re-gapping the plugs did nothing to help. So, continuing to research I found a youtube video in which the tech was diagnosing a similar issue. In his video, he used the fact that the ignition coil has complimentary cylinders & a waste spark system, so 3 & 4 both fire at the same time, every time (2 & 6, 1 & 5). I did the same on my truck, moving the Cly 1 wire to the Cyl 5 position and vice-versa. Sure enough, the code threw for Cylinder 5!!! If it was a fuel or air issue, the misfire would have surely stayed on Cylinder 1.

So, I already have plugs, wires, and a new ignition coil on order and will be changing those out. At this point, I fully expect this to solve my problem. I hadn't seen the "move the wires" trick here before, so this will hopefully be helpful to someone!

Link to the video that helped solve this mystery:

 

I wonder if this is also with the 4.0 this sort of thing happened to me a few years ago the intermittent misfire so I did a tune up and it seemed to fix the issue but now off and on for the past say month it is happening again I also remember when this first started to intermittenly do this the weather was cooler and wet also my truck sat for at least 1 day. over this past week end my truck sat for two days and when I went to drive it last night it fired up idles decent but then when I dove it it had the misfire and the engine light flashing but if I feathered the peddle and kept driving when the engine warmed up the misfire would leave . also later on when I would be sitting in my truck and have to fire it up to defog the windows it seemed to run a little shaky on idle but only at idle I really dont want to have to redo the dam plugs that one plug is really hard to get at and wit hthe weather like this rain most of the time and having to work outside in the parking lot with tight spots no room not a good thing lol

 

I've replaced the ignition coil. The two cracks in the sealant epoxy were very noticable (see below). The truck idles and runs like an absolute dream now. I would definitely recommend at least removing and inspecting the ignition coil for cracks like this, including in the housing itself, for anyone encountering the same issues.

 

I would definitely look at that. In my researching this, I found that these ignition coils developing cracks over time from the heat tends to be an issue. Where I saw that was on F150s, so if they're using the same coils that our 3.0 Rangers are using, it would make sense a 4.0 Ranger has the same box.

 

Thanks for the follow up and pictures!

 

Good find and a REAL GOOD lesson for everybody.

Here's a dumb question: Could those cracks be repaired with epoxy or silicone rubber?
Just wondering if anyone ever tried it.
Obviously not while paying "garage rates".
I realize coils are not expensive and such experimentation would take time and effort.....but with all the Fords out there....?