Just took ours back to a mechanic today. We are borrowing my son's 99 while he is on his honeymoon. I'll post what happens. Hopefully, they will find out what's wrong and have an answer for all of us.

 

After all the stuff I had replaced on mine, it's STILL doing it! No "Check Engine" light.

On mine, the idle drops to about 500-600rpm, sitting at a light, in gear, foot on brake. It starts to idle rough like it wants to stall.
Putting it in "Park" raises the idle by about 100rpm and it smooths out a little.

It has been worse today and yesterday, with the warmer weather.
I am starting to think small vacuum leak somewhere, maybe even a CAT starting to fail, allowing emissions to accumulate.
It could also be a dirty throttle body, or something else wrong with the EVAP.

Would a small vacuum leak somewhere trigger a "Check Engine" light?

I would think that if it was something major in the engine, like timing chain, the rough idle would be rhythmic, not intermittent.

 

Mechanic called and said an O2 sensor was showing a bad code. Replaced the sensor and said the new one showed more out of tolerance than the old one. He's going to put the old one back on tomorrow and said he doesn't know what else to do other than to start tearing it down and looking for a problem like an injector or internal seal. He advised to drive it until it fails continuously and then bring it back in. I'm still scratchin' my head. Boy I miss having hair

 

Took mine back today, they say that they can't find anything wrong.
They say that it has an engine "wobble" that is "normal" for an Explorer with 136K miles on it.

The good news is that the throttle body is clean, and they don't believe that there is any major mechanical issues (timing chain, piston, cylinder compression, etc.).

They said that the technician did go through the PCM and raised the "curb idle speed". Hopefully that will help. Apparently he didn't see any need to check the oil separator. They said that ANY vacuum leak would trigger a CEL.

I guess I'll just drive it and wait for the CEL to come back on.....

 

Anyone else get this problem solved? I still can't figure this one out.

 

I never fixed mine completely. I still had a slightly rough idle but it ran great and had no ill effects on drivability or fuel mileage so I stopped working on it. Mine is a stick so no big deal.

Sorry,
Bob

 

I thought I would chime in with my .02. I have a 2002 sport trac 4.0. 123k, just got it a month ago. It had a bit of a miss at idle and ran a little rough at around 60 mph that felt like it was missing, but no codes.

The idle miss got worse each day it seems, to the point I was afraid it would die (but it never did). Then I got a cel, the codes were no. 6 misfire and crankshaft sensor. Checked the wires and plugs (brand new), replaced the crank sensor, checked the coil pack, the MAF, the TPS, all fine. cel went of but idle was worse than ever.<O</O
<O</O
I was sure I had a vacuum leak, but all attempts to locate it failed. Thinking it may be injectors (or at least that it wouldn't hurt) I ran some sea foam through the system, in the oil and the fuel.
<O</O

Much to my surprise the idle smoothed out instantly, and although its just been a day it no longer misses!<O</O

<O</O
My only explanation is that by pouring the sea foam down the PCV pipe broke loose a stuck PCV valve. I had not checked the value for 2 reasons, first I didn't know where it was (it's a new truck, to me) second, I've never had a PCV valve stick (although reading the forums that seems to more common than I thought).<O</O
<O</O

Since then I pried the valve out and confirmed that it is functioning just fine - but I wish I knew for sure that that is what caused the idle problem - too late to determine that now.<O</O
<O</O

Any way, this particular thread helped me a lot getting my thinking of what would cause such a rough idle issue. Searching the Internet it seems a lot of circa 2002 explorers have a rough idle problems, some related to the nature of the motor, I suppose, others related to the fact that there are at least a dozen components that could cause it - and on a 123k mile vehicle things start to go.<O</O

Anyway, after having checked about a 1/3 of the components, I at least have the satisfaction of knowing most of the engine system is in good shape.<O</O
<O</O

So thanks to you guys for providing the inspiration I needed - and boy am I glad (crossed fingers) I got this under control. To me a smooth idling engine is very good thing.<O</O
<O</O


kpg<O</O

 

OK. I'm being punished by the car gods for this one.

The rough idle is back. Not quite as bad, in the sense that sometimes it does not occur, but when it does it's just as bad as it was - missing a lot - and its also noticeable on initial acceleration at times.

So riddle me this: I replaced the crankshaft sensor, then for 24 hours it idled fine - then started acting up again. Then after much poking and prodding I used the sea foam and it cleared up for 24 hours now it's back.

Pouring a liquid in the vacuum system may temporarily seal any vacuum leaks, but how can a crankshaft sensor (that obviously was not the problem) temporarily fix the problem?

I guess it could be a coincidence, I'll keep trying things out.

I ordered a OBDII cable for my laptop, shipped from Hong Kong, will be here in 8 days - till then...

kpg

 

With odb ii code P0306 - Cylinder 6 misfire, I knew what to check.

Plugs, wires, coil, compression, vacuum leaks, faulty/clogged injector in that order.

Plugs looked brand new (only had the truck for a month, prev owner said he did a tuneup).

wire resistance tested ok

coil resistance checked ok

compression ok

could not find any vacuum leaks, inspected all lines, used propane around intake

injector was clicking, ran a few tanks of injector cleaner (gas added cleaner is more of a preventative measure but I do not have the equipment to perform a proper in engine cleaning).

Tested every sensor, ensuring proper supply voltage and any sensor tests.

After much effort still had bad idle, missing at all throttle positions, and it was getting worse.

I was about to replace the coil pack (I figured weak spark) but I first decided to start back at the beginning, so I bought 6 new plugs and...yes...that fixed the problem.

I put the old #6 plug back in (it looked fine) thinking maybe the plug wire was not snapped in and that caused the missing - and the engine
misfired again. Swapped it out to cyl $5 - same thing.

So plug #6 was faulty - a new (few months old) plug with no visible
defects caused all this grief.

One good thing from all of this - I bought an ELM 327 usb cable and am trying out different software - wow - how did I get along with out this stuff?

kpg

 

Congrats!

My rough idle is still present, not getting better or worse. I've learned to live with it.

 

My wife drives the Explorer. I just hate it for her. She has enough to put up with just living with me. I would like her car to be trouble free.

BTW, I've never heard of checking for vacuum leaks with propane.

 

Well guys, I had a miss that I chased for yrs, changed wires and plugs every 5k, temp fix.

One day on a hunch I took my plug thread chaser and ran it down all 6 of the plug holes. Put a new set of Autolite plugs in and 15k later still smooth.

My guess, a little carbon on treads caused enough resistance that the waste spark system didn't like it.

On another note my son's X5 (BMW) cost him $$$$ for factory techs to run diagnostics for similar problem, finally he brought it to me. They had performed the spray and propane leak tests numerous times.

I built a smoke machine out of hose and a party smoke machine (non toxic water based) and injected the smoke +5psi from my compressor into the intake manifold, and lo and behold we see 2 streams of smoke from under his intake manifold. 2 "O" rings @ $.50 each and all fixed (we did splurge and replaced all 6 while we were in there..

Good note, I now have a smoke machine for testing ($70.00), and unhook my tubing and the kids have smoke for their Halloween parties..

 

Same issues, rough idle, but mechanic cannot seem to find the source,
The following has been done, some more than one time, new plugs,wires, coil pack, EGR valve, Fuel injector(s), Smoke test, (they R&R the intake system based on a small leak which was found, actually did this twice)Still not correcting the rough idle, then did compression tests, leak down tests, fuel pressure test, intake and exhaust temp tests, at which point they said the valve springs were bad, so they took off the heads and sent them to a machine shop, heads were in good condition, no bad springs, had them cleaned up, then noticed they damaged the timing chain/tensioner in the disassembly process, so they removed the engine so they could install a new timing chain/tensioner, then reinstall the reassembled engine, and it still has a rough idle. Not sure where to go at this point. Any suggestions............

 

We're still living with ours having the occasional rough idle. Someday one of us will stumble across the fix.

 

Did anyone figure this problem out?

I have been chasing a high idle ~ 950 -1000 rpms (rougher than normal)

I have used propane, starter fluid and have found no leaks this way.

I have new O2 sensors, PCV, MAF, EGR, IAC, Throttle body & TPS, cleaned upper and lower intakes with new gaskets, new coil, wires, plugs, new timming chains, gears, tensioners, guides, HV Oil pump, all new gaskets, water pump, main & rod bearings etc....

The only thing that makes sense is a vacuum leak. The compression and leak down test results are very good and vacuum gauge results check out fine.

But still a vacuum leak is the only logical problem.

A couple of days ago, I removed the two pcv vacuum lines from the back of the intake manifold and plugged these holes on the intake, and just let the pcv exit into the atmosphere. Mind you, I still have the hose from the intake tube connected to the passenger valve cover.

This cured my high and rougher than normal idle! (progress)

I drove it this way for a day and it worked perfect. I can even tell the power brakes are stronger. (I never had a CEL)

I then took a pcv valve and inserted it backwards (so the flow can only move from intake tube to valve cover) into the 5/8" hose from intake tube that goes to the valve cover.

I noticed that the backward flow in the tube is very small at times (which goes right past the pcv valve I put backward in the 5/8" hose), so I have found a check valve with spring that holds it closed and only that takes 1/2 psi to open in the one way flow direction that would work better in blocking all vapors flowing into intake tube and allow it to flow into the crankcase as needed.

Sorry for the long post...

I suspect the air/oil seperator (FORD PART# F77Z-6A785-AB) (having two small O-rings) is leaking or the hose from the air oil seperator to pcv valve is leaking or both.

It is a pain in the a** to replace. The air/oil seperator is located under the lower intake manifold and wiring harness at the rear of the engine (in the cam valley). (It looks like a little black plastic box) The first gen explorers I believe have a similar one, but made of metal.

I plan on replacing the air/oil seperator and pcv tubing, as well as place the check valve and a new 5/8" hose from intake tube to valve cover.

I already have a air/oil seperator (aftermarket from JEGs) installed after the pcv valve, by adding the check valve to the intake tube to v-cover path, their should be no un-metered air entering the intake and very little oil entering.

I will post back my results.

If this does not fix my problem, then what else could it be?
Why else would the engine run perfect with pcv removed from the vacuum system?

Could it the their be a leak in the block somewhere? (pan gasket, crankshaft seal, valve cover gasket, front timing cover)


This would have the same affect as removing your dip stick or oil filler cap.