Random rough idle, random perfectly smooth idle, no engine code. Please help!

[Blind]

Originally this sprung up and I got a code of 0300, multiple/random cylinder missfire. After replacing a few parts and clearing the code the code has not come back, however the symptom remains.

It happens at idle, but it also occurs all the way up the rpm band, it's a very rough choppy misfire accomponied by a massive loss of power.

It only does it 1/10 of times I come to a stop, but I do feel it occasionally while on the roll and under throttle as the engine doesn't rev as easily. If I give it WOT through a gear it will usually go away. However if it's doing it at idle and the car isn't moving, if I put it in park and rev it the roughness does not go away.


parts I have replaced and items I have cleaned/checked:
Motorcraft fuel filter
Motorcraft spark plug wires
Autolite platinum plugs gapped at .054, installed with dielectric grease, and yes they are seated firmly
Replaced the coil pack unit with one I bought off here.

cleaned the IAC, cleaned the MAF
checked the fuel pressure, fine
checked the vacuum at idle and reved, it is in spec according to my shop manual, same with fuel pressure.


I had a similar rough idle when a shop that changed my oil and "inspected" the air filter neglected to hook up the PVC hose and unmetered air was being let in, but I can't find any cracked or loose hoses, (I checked with a propane bottle while at idle) and since it's completely random I dont think it is caused by that, plus that immediately triggered a CEL and the CEL is not lit.


any help please? I'm pretty much sick of this :roll:

 

[BradE.]

Hmm, looks like you've covered the basics. If it were the IAC I wouldn't think it would do it up in the power band, they usually only got nutzo at idle.

Perhaps a throttle position sensor is sticking a bit? You have no vac leaks either?

 

[rizzjc]

Did you try giving the throttle body a good cleaning?

 

[Blind]

throttle body is fine.

I'm fairly certain it's a sensor issue, grounding issue, or unmetered air, but I have no idea where to go next since there is no codes.

I was hoping somebody here had run into the same symptoms.

 

[LARRYN]

Blind,
I feel your pain ! My 99 4.0 sohc has come up with the same problem. After taking it to my mechanic who suggested i take it to ford they couldn't locate the problem. The same misfire code came up but they said it could be multiple things to cause that. They never got a pressure gauge on it while it was in bog mode but the mech thought it could be a fuel pump. I just cleaned the map and had all the same maint. done on it too.

 

[Turdle]

Try this
Disconnect the maf sensor- run it like this.
It will trigger a CEL- however you want to notice if it "runs" better

 

[LARRYN]

Smitty,
I will try that today as i am going to take it on a 500 mi trip. I am wondering too if with there is some dirt or water in the gas nowadays that is causing it. I'll throw a bottle of heet in there too.

 

[Turdle]

Smitty,
I will try that today as i am going to take it on a 500 mi trip. I am wondering too if with there is some dirt or water in the gas nowadays that is causing it. I'll throw a bottle of heet in there too.

Ooooo
I don't know if I would run it this way for 500 miles. Plug the maf in for the trip.
Idea
If you notice a difference, stop at a salvage yard along the way for a used maf ( if this is indeed the culprit)

 

[LARRYN]

I was going to try it in the driveway only.
There was a thread somewhere here where they are using one from a mustang 89-92 bought at the bone yard.

 

[Blind]

nice, I have a couple stock mass air sensors in my garage from my mustangs

 

[aldive]

Any updates?

 

[Blind]

have not found a fix, it died on me 3 times on sunday.

I am replacing the battery (which was dead 1 day after a 800 mile roadtrip) and the IAC valve tomorrow, I had to order the parts and they'll be in tomorrow.

I ohm tested the IAC, and it was at 10ohms, but from either of the connectors to the case of the IAC made no change on my meter, it just sat with a "1 . " on the screen which is how it looks with nothing connected to the needles.

also, a mustang MAF sensor will not work on my truck, at least it is not a direct swap.


I also spent roughly 5 minutes with a can of propane while the truck was idling (Smoothly of course) this afternoon and I was not able to find -any- vacume leaks, it never stumbled. I followed every vacume line and sprayed it all around the upper/lower intake mating area and the fpr, and all of the sensor locations and hoses on the intake tube.






I drove the truck about 800 miles roundtrip this past weekend, the battery was dead the day I left, I jumpstarted it, threw the jumper cables in the back, drove to my sisters to visit for the weekend, drove there friday night, it sat all day sat, sunday went to start and the battery was dead, jump started it, drove home, and when I stopped for lunch/gas it was running -really- rough, when I restarted it the truck died, restarted again and it only ran with me keeping my foot in it to hold the rpm's up, it died when I backed out of my parking spot and shifted to drive, started again and kept my foot in it and 2-footed my way back onto the freeway keeping the rev's up :roll:

I tested the battery and 1 day after that trip, the battery was at 10volts, I jump started it and it read 14.6volts, so the alternator is good I assume. When the truck is idling rough the voltmeter fluctuates quite a bit, I hope that is because of the idle dancing around and the alternator is speeding up / slowing down, and not a stupid problem with the alternators internal regulator?

after that trip my truck now has 100,530 miles on it.

 

[Blind]

still working on it, I replaced the battery as the alternator came back as testing fine.

I've been driving around with a fuel pressure gauge hooked up to the shrader valve, it idles at 30psi when warm, koeo it's at 36psi.

when I turn it off, the fuel pressure does not bleed down at all within 20 minutes.


I reset the MIL (code 0300 again) and cleaned the MAF sensor wires again.




it seems like I can get the truck to idle rough if I want to now, if I come to a sudden stop it will run rough, and if I put it in neutral and rev it once it will idle smooth again.

 

[pdesocio]

Shot in the dark

It sounds like you are extremely thorough, but I will throw this out there anyway. Have you noticed any coolant loss? No wet plugs when you changed them out? I had many of these symptoms with my Taurus. Power loss was so bad at times my lights would dim even at 65 MPH/2600 RPM. Eratic RPMs when I came to a sudden stop. Did a complete tune up and cleaned the MAF etc etc...Turned out to be the beginning of a bad head gasket. At first it didn't leak so bad and when I changed the plugs I could see fowling but no moisture. The amount of fluid on the plugs caused the 0300 code, but apparently was not bad enough to be seen. Good luck...I KNOW how frustrating this is!!! :fire:

 

[aldive]

Have you checked the DPFE?

 

[Blind]

Have you checked the DPFE?

the DPFE malfunctioning would set a code P0401 or P0402, not P0300 (random/multiple cylinder misfire).


how would I "check" it without having a scan tool that does that?

 

[Blind]

It sounds like you are extremely thorough, but I will throw this out there anyway. Have you noticed any coolant loss? No wet plugs when you changed them out? I had many of these symptoms with my Taurus. Power loss was so bad at times my lights would dim even at 65 MPH/2600 RPM. Eratic RPMs when I came to a sudden stop. Did a complete tune up and cleaned the MAF etc etc...Turned out to be the beginning of a bad head gasket. At first it didn't leak so bad and when I changed the plugs I could see fowling but no moisture. The amount of fluid on the plugs caused the 0300 code, but apparently was not bad enough to be seen. Good luck...I KNOW how frustrating this is!!! :fire:

the plugs that came out of the truck when I replaced them had no signs of corrosion, the plug gap was too large but they were all light grey.

I had a blown headgasket on my mustang back in Jan. and one of the plugs came out rusted and wet as the only sign other than overheating and occasional hydrolocking when starting.

 

[timleedude]

It seems like a guessing game now.. Since you tried the IAC, now I would try replacing the Mass Airflow Sensor. My 89 Corvette had almost exactly the same problems and when I took it to the dealer, they changed the MAF and all was good.. and somehow the defective MAF didn't throw any error codes either.

-Tim

 

[aldive]

the DPFE malfunctioning would set a code P0401 or P0402, not P0300 (random/multiple cylinder misfire).


how would I "check" it without having a scan tool that does that?

There is a good thread on here about it.

 

[Blind]

It seems like a guessing game now.. Since you tried the IAC, now I would try replacing the Mass Airflow Sensor. My 89 Corvette had almost exactly the same problems and when I took it to the dealer, they changed the MAF and all was good.. and somehow the defective MAF didn't throw any error codes either.

-Tim

I was going to swap the sensor with a spare I have from my mustang but the plug is a different shape, it's still 4 wire but the mustang plug is round while the explorer's is more rectangular...