Check engine light / rough idle

[davem]

Well, here we are: a week later, 2 trips to the local shop, and no progress.

The problem (rough idle) seems to only occur on a cold start, and goes away after warm up. Yesterday, the Explorer had sat for 4 hrs at the shop, but because it was warm here (45 F in MN), the rough idle was very brief, thus no chance to diagnose,

We've kinda ruled out plugs, wires, coil, vaccuum. The MAF was cleaned. I cleaned the IAC (maybe the IAC went bad ? can it be tested ? hate to spend $100+ to 'try' a new IAC.)

This morning, in my garage at 42 F, the idle was very rough. Within 5 miles of driving or less, the problem goes away.

Can anyone make any additional suggestions as to things to try ?

Dump in some injector cleaner ?

Getting frustrated enough to consider dumping this thing, but other than this, its a pretty good vehicle.

Thanks.

Dave

 

[Firestorm]

Is it throwing any more codes? Sounds like it could be intake gaskets. This started from a cylinder misfire though?

You can try some injector cleaner it will do them some good, but I don't believe this will solve your problem.

 

[davem]

According to the guy who read the code, just the P0306.

Could it be a bad sensor somewhere ?


Is there a way to test the IAC ?

 

[gavin]

I would test the plug wire; per Chilton's, resistance should be under 7000ohms for every foot of length. Anything over that could cause issues. Maybe put the plug wire in the fridge or freezer for 30 min or so for it to get cold, then test resistance
since heat and cold cause metal to expand/contract.

it could possibly be the coil pack; there may be a way to test it, I haven't looked at my Chilton's for that.

 

[Firestorm]

Did you guys just do a visual inspection of the plug wire for cylinder #6? How were the plugs and wires ruled out?

Take Gavin's advice and test the ohms of your plug wire.

As for the IAC, via Haynes. Start with KOEO, probe the harness. Should be 10.5-12.5 volts. This shows whether the IAC valve is receiving the signal from the PCM.

If it is has the proper voltage; measure the resistance across the terminals on the IAC valve. There should be 6.0-13.0 ohms. If the resistance is incorrect, replace the IAC.

Measure the resistance from either terminal to the IAC body. There shold be 10,000 ohms or greater. If less, the internal circuitry is grounding against the case.

For the coil packs. With the ignition off, disconnect the electrical connectors from the coil. Connect an ohmmeter across the coil positive terminal and each negative terminal. The resistance should be 0.3-1.0. Primary.

If this checks out. Connect the ohmmeter between secondary terminals (the one that the spark plug wires connect to) of each coil pack. The resistance should be 6.5-11.5 K-ohms. You should be checking #2 and #6 coil pack, it is paired.

Haynes manual is calling for the spark plug wires' resistance to be 5,000 ohms per foot.

Good luck, hope this helps.

 

[davem]

Did you guys just do a visual inspection of the plug wire for cylinder #6? How were the plugs and wires ruled out?

Take Gavin's advice and test the ohms of your plug wire.


If it is has the proper voltage; measure the resistance across the terminals on the IAC valve. There should be 6.0-13.0 ohms. If the resistance is incorrect, replace the IAC.

Measure the resistance from either terminal to the IAC body. There shold be 10,000 ohms or greater. If less, the internal circuitry is grounding against the case.


Haynes manual is calling for the spark plug wires' resistance to be 5,000 ohms per foot.

Good luck, hope this helps.

OK, here are my findings:

IAC reading across the terminals = 8.9 ohms, which is in the acceptable range.

The IAC ohms reading from terminal to IAC body was non-existent, so I guess that good - its not grounding to the case.

How much should the plunger move ? I'd say it moves very little, maybe 1/8" - 1/4" tops. It does not move extremely freely. I cleaned it a couple weeks ago - still looks pretty good.

I tested the ohms of plug wire # 6 because cylinder 6 had the misfire - it read something like 5.41 when on the 20K ohm setting (so is that 5410 ohms ? if so, it should be ok. the plug wire is a little over 1 foot long.)

I disconnected the battery to reset the code, and I'm happy to report that in 4 hrs or so, with probably 5-10 on/off cycles, the CEL has not re-appeared.

I don't know if the IAC cleaning helped, or the injector cleaner that I added to a near empty gas tank before filling it up a few days ago helped, or maybe the slightly warmer temps (approx 30 F) is keeping the rough idle from re-occuring.


Anyway, I'm open to comments on the readings I measrured, as well as the movement (or lack thereof) of the IAC plunger.

Thanks.

Dave

 

[wyochimneysweep]

i'd say the wire is bad. its not oil soaked or anything like that?

 

[davem]

i'd say the wire is bad. its not oil soaked or anything like that?

The #6 plug wire ? No, not oil soaked.


Are you assessing it as "bad" due to the ohm reading ?

 

[wyochimneysweep]

that you have no problems know could be cuz you removed it and reistalled it. any oil at all will cuz a spark to trace and not fire that clynder right. new wires are cheap and easy but don't go to cheap or you will get a bad wire again. pulled a bad wire directly out of a box

 

[Buffalosports]

I had the same code come up on my 00 Sport. It was because one of the plug wires had started to ware out and the wire was showing. Couldn't tell because how the wires are ran from the factory under the intake(poor design IMO). Put some new Bosch plugs and wires on and it fixed it right away. I ran my wires over the engine so I could keep an eye on them and prevent it from happening again.

I hate those plugs and wires are situated on the Sport. The driver's side is very easy to change but the passanger's side is terrible.

Hint: You probably already know but the best way to get to those is by making a slite tear in the wheel well. All 3 are right in reach.

 

[wrigley_1285]

I hate those plugs and wires are situated on the Sport. The driver's side is very easy to change but the passanger's side is terrible.

Hint: You probably already know but the best way to get to those is by making a slite tear in the wheel well. All 3 are right in reach.

I didn't make a cut instead I just use a couple of swivels on my socket wrech with different sized extentions. It was still difficult though.

 

[Buffalosports]

I didn't make a cut instead I just use a couple of swivels on my socket wrech with different sized extentions. It was still difficult though.

Yea I thought of that also but how did you reach the boot? I couldnt even get my hand down there without taking anything off. That metal tranny tube is directly in the way (on the 98 Sport atleast)

 

[Firestorm]

Yea I thought of that also but how did you reach the boot? I couldnt even get my hand down there without taking anything off. That metal tranny tube is directly in the way (on the 98 Sport atleast)

Next time unbolt the transmission tube so that you can move it out of your way to get to #2 spark plug.

The IAC ohms reading from terminal to IAC body was non-existent, so I guess that good - its not grounding to the case.

Davem, the ohms should be 10,000 or above or the internal circuitry is being grounded.

I can't recall at this moment how far the plunger is able to move, seems to me that I had moved mine about a 1/4 of an inch, and didn't try to move it farther.

As far as temperature is concerned, I don't believe that it would make that much of a difference, seeing as you are stating it is still below freezing.

That is good that the CEL hasn't come back on yet, it could be anything that you have done to get rid of it. Let us know if it comes back.

 

[Buffalosports]

Next time unbolt the transmission tube so that you can move it out of your way to get to #2 spark plug.

I didn't know you could unbolt it. It is the tube to put in the tranny fluid.

 

[Firestorm]

Yes, there is one bolt that holds the transmission tube.

 

[Buffalosports]

Possible distributor problem? Useually distributor and distributor cap problems are more associated with the amount of moistor that gets into them but could the temperature cause a problem? You said the wires and plugs are fine but it is still reading plug #6, possibly plug #6 is not getting sufficant amounts of power from the distributor.

 

[Firestorm]

Possible distributor problem? Useually distributor and distributor cap problems are more associated with the amount of moistor that gets into them but could the temperature cause a problem? You said the wires and plugs are fine but it is still reading plug #6, possibly plug #6 is not getting sufficant amounts of power from the distributor.

Distributorless motor, Buffalo, just the same as yours bud. We're working off of coils. Davem, did you ever test the coil pack?

For the coil packs. With the ignition off, disconnect the electrical connectors from the coil. Connect an ohmmeter across the coil positive terminal and each negative terminal. The resistance should be 0.3-1.0. Primary.

If this checks out. Connect the ohmmeter between secondary terminals (the one that the spark plug wires connect to) of each coil pack. The resistance should be 6.5-11.5 K-ohms. You should be checking #2 and #6 coil pack, it is paired.

 

[Buffalosports]

Distributorless motor, Buffalo, just the same as yours bud. We're working off of coils. Davem, did you ever test the coil pack?

Sorry, couldn't remember. I knew there was something different about the distirbution in the ex's. All is the same in the end anyway. Check it, could give you similar problems as I explained before.

 

[davem]

Distributorless motor, Buffalo, just the same as yours bud. We're working off of coils. Davem, did you ever test the coil pack?

Not yet. I've gone 2 days now without getting a CEL (fingers crossed).

I'll save that for the next round.


Based on my IAC description (degree of plunger movement), should I consider it normal ?

 

[davem]

Davem, the ohms should be 10,000 or above or the internal circuitry is being grounded.

Can you describe exactly where to make contact with the IAC ? I had a lead on the electrical connection terminal (tried each of them) and a lead on the silver-ish 'body' of the IAC - is that not the correct place to measure ?