Rough idle on cold start up

My 2001 Explorer XLT V6 with 126K miles has had a rough idle at start up for awhile (1 - 2 years). Sometimes it barely keeps running and dies. This has been going on awhile, but seems to be getting worse, so I think I want to resolve this before winter sets in (MN).

Sometimes the check engine light comes on and stays on for weeks. Sometimes the CEL goes out, and does not re-appear despite some very, very rough starts. Even after a rough start, by the time I'm a mile down the road, its running good. On a warm start, it runs/idles fine.

I've owned this rig for the last 90K miles (2nd owner) and have never replaced plugs or wires. I would think its about time for plugs, and maybe even wires, but I'm just not sure - would they only affect a cold start ?

The intake o-ring situation that I've read about here seems like a possibility - are there any other tell-tale signs to support this idea ?

I'll also mention that its got a bit of a vacuum issue - will blow air through defroster vents instead of dash vents (even though dash vents were selected) under load, going up a hill. This has been going on for at least 5 years. But I thought I'd mention it in case vacuum may be part of the overall issue.


Any advice on how to attack this.

Thanks.

Its the intake o ring situation. Same exact thing happened to me and now it's fixed.... Common problem

I took the Explorer to the shop Sunday night so they could experience a 'cold start' on Monday. Unfortunately, it idled very smoothly. I was shocked and even went there and experienced the smooth idle on a cold start.

So I left it over night again, and it started/idled great on Tuesday morning, too.

The air temp has been bottomed out around 40 F the past few nights ..... and maybe thats a little warmer than when I was getting the rough idle. I'm gonna pick up the Explorer and bring it back when its a little colder, but my question to those who think its the intake O-rings/gasket:

Is this (the intake issue) air-temperature sensitive ?


I guess it kinda makes sense, but wanted to mention this in case it points to a different possible solution.


PS - The intake fix is gonna be about $300 - does that seem reasonable ?

When it's cold outside, the rubber o-ring intake gaskets shrink, which causes a lean condition, thus the rough idle. Once the engine starts to get warm, the engine heat causes the gaskets to expand and thus your idle improves. I had the same problem when my truck only had 42,000 miles and the dealer replaced them free of charge due to a TSB. $300 seems about right...maybe a tad bit high, but not too much.

I really believe the intake O-rings are the problem, or at least part of it.

But this thing has now gone in another direction - I'd like to get your comments.


Tues night, after leaving the Explorer at the shop for 2 nights/2 days, where the cold idle issue could not be re-created, I picked up the Explorer to drive it home. The air temp was probably in the low 30s F, so I expected the cold idle issue, but it seemed to idle OK when I started it.

As I drove it home, it started 'bucking'/surging. The Check Engine Light came on. And at times, the CEL would blink for a few seconds, then remain lit. It really ran bad, loss of power, etc.

I kinda hoped that some of the shop's diagnostic techniques (sprayed carb cleaner near intake to test for leak), were the cause and would soon work there way through the system, but I've driven it at least 30 miles now - and its still running bad, CEL on, CEL blinking sometimes, etc.

I trust this shop - I've gone there for 10 years, so I kinda doubt its intentional. But for this (buck/surge) to happen, somewhat out of the blue, right after they tested it, kinda makes me wonder.

I went back to the shop today, and they read the codes (2 of them) :

cylinder 6 misfire
a n d
multiple random misfires (mechanic's words)


They want to put in new plugs and wires, which is understandable at 126K miles (NEVER replace before). But originally they told me plugs/wires were not the cause (of the cold idle problem).

I'm struggling with this - does it make sense that plugs/wires are affected by air temp and can cause the cold idle issue that used to go away after it warmed up ?

And did the air temp suddenly drop enough to cause the bucking/surging ?

Thanks.

Dave

The two issues can not be related, at least in my mind. It can be coincidence that this issue started while at the shop, or the shop messed with something and broke it. cold temps cannot cause a misfire.

i would check and make sure that all of your wires are going to the correct location first. perhaps the shop pulled them and put them back in the wrong order creating the wrong firing order.

BurnTheLight88 said:

The two issues can not be related, at least in my mind. It can be coincidence that this issue started while at the shop, or the shop messed with something and broke it. cold temps cannot cause a misfire.

i would check and make sure that all of your wires are going to the correct location first. perhaps the shop pulled them and put them back in the wrong order creating the wrong firing order.

Click to expand...

I'll check that.


Could something in the plug wires/connectors have broken while unplugging/re-plugging ? If so, is that most likely due to age ........... or negligence ?

wow. when i read your original thread i had to check to make sure it wasn't one i had written about my 2001 sohc v6 a couple of months ago. exactly the same symptom’s (at least until you took it to the shop) even the defrost/vent issue.

firstly, there is no doubt in my mind that you have a small vacuum leak and that's what is causing the default to defrost mode issue when you put the engine under a load. i located my leak, sealed it a have had no further problems. that being said, it has nothing to do with you rough cold start issue.

the common wisdom regarding the rough idle on cold start is the intake "O" rings. i haven't changed my yet, but i plan to and am reasonably confident this will fix this problem based on the advice given by other forum members.

As far as your experience after leaving the shop... i agree that the most likely cause of the surging/bucking is a bad plug wire or a crossed plug wire. i doubt your shop did anything on purpose, but anyone can make a mistake and anyway your plugs and wires are due for replacing.

$300 sounds a little high to me. the "O" ring seals (upper and lower) aren't much, but it's supposed to take several hours to change them. i guess it depends on how much your shop will charge you for parts and what their labor rate is. I plan on doing the job myself and expect it cost me under $50 even with a new thermostat and seal. If the $300 includes changing your spark plugs and wires it's a good price (especially if you live where they salt the roads in winter as getting the plugs out can be very labor intensive).

I had the plugs and wires replaced, and so far it starts well. I still kinda expect the cold idle issue to return, but it has not so far (and the temp has dropped to low 20s).

I'm surprised (and glad) the the plugs/wires seems to have solved this.

The shop who does my Explorer repairs seemed hesitant to replace the intake gasket because they could not reproduce the problem (might not have been cold enough at the time).

They talked about spraying carb cleaner near the intake while its running rough ... if it sucks it in through the leak, it runs better temporarily - does this seem like a valid test method ? Can someone pinpoint exactly where I would point the spray ? Is there a better test that I could perform to prove its the intake gasket ?

One thing that I will point out ......... it SEEMS like if I fully depress the gas pedal before starting the engine, it seems to idle better ..... it might still stumble a bit, but if I tap the pedal again, it then settles in to a fast idle and later falls back to a the expected idle speed once warmed up. This pattern may not be the case 100% of the time, but thought I'd share it in case this points me in another direction.

Is the O ring that you are all referring to in the upper intake or does this involve removing all of the intake, upper and lower? I am experiencing these same problems and am considering replacing the gaskets as needed but sure wanted to be sure before I tear everything apart. I personally found it difficult to spray carb cleaner accurately around the intake due to all the obstructions.

It was the lower o-rings leaking on mine and i had exactly the same idling problems as mentioned above,it was worse the colder it got.I found an excellent how 2 guide on here and did the job myself.i couldn't belive the difference it made to the car (98 4ltr sohc).

My 94 Ex with 130K idled rough when cold for about 30 seconds every morning for months.....it eventually turned into a constant mis fire and chugging for two days. I found one plug that was wet looking while all the others were bone dry. I cleaned the plug and swapped it to another cylinder....intermiittend miss fire. Replaced all the plugs with Motorcraft Platinum and it now runs better than ever. Inspection found one of the plugs was cracked
after only 30K miles.

Reminder:
2001 V6 XLT
147,000 miles

Well, its over 2 years later, and I finally had the intake upper and lower gaskets replaced at shop. When I picked it up, they mentioned something about maybe needing to replace the plenum if the gaskets did not resolve the problem. They did not say it obviously needed replacing .... just mentioned it.

When I first picked up the Explorer, the cold start idle was not great, but they said some cleaning materials may cause a temporary issue. (Seemed weak, but I played along.)

The first 2 days it seemed to stumble a bit at first during a cold start, but smoothed out pretty quickly. Note that I was using my block heater, which may have improved my overall situation. But its gotten progressively worse since then (and I'm not using the block heater). Its still 'better' than when I took it in, but not much better. My 'check engine light' has returned - have not have the code read yet. I'm going back to the shop.

My plugs and wires are about a year old.

Any suggestions on what to try next ?

plenum ?
O2 sensors ?
Idle Air control valve ?
MAF sensor ?
Other ?

Thanks.

Not sure if problems on 94's are relevant to 2001 but what I learned on the 94's is they like to over heat and crack the spark plug in cylinder 3. This is the plug that is a bear to change. ( the trick is to access the plug thru the wheel well.) after only 9 months with new Motorcraft platinums, the 94 started to misfire again. By disconnecting wires at idle it became clear the good old no . 3 cylinder was the issue again. Upon removal, the white ceramic outside was charred to a brownish orange. I installed a new plug and she idles perfect again. Maybe 94's need heat shields over the plugs to protect them from radiant heat from the exhaust manifold?

The shop says its a cylinder 6 misfire. So they replaced the plug (turns out my plugs were about 3 years old - older that I thought). They also said if this does not resolve the misfire issue, I may have a burnt valve, from driving it too long with the misfire going on ........... I'd be OK with replacing a plug every 3 years, but not gonna spend the estimated $1600 for a valve job.

I would find a new shop. A good shop would know where to spray the carb cleaner to test it. BTW carb cleaner isnt recommended, it's flammable. I've heard Brake Cleaner is a better choice.

I have the same symptom you had, at 210,000 miles. Only when cold, lasts about 20 seconds. Noone on this thread has suggested what I lean to. I suspect the Coolant Temperature Sensor is weak, not reading the temp correctly when cold. So the computer doesnt know its cold, so it doesnt "choke" the engine as it should. If there's an Ambient Air Sensor that could be the culprit.

I haven't gotten a Check Engine Light yet.

Steve

Ever since the plug was replaced, my Explorer has been doing great with its cold idle. No more Check Engine Light either.

I think the intake gaskets were a huge part of the improvement.

We're below zero almost every night, so I've had many chances to see if its working.

I'm not sure if they put in a new plug, or just found a loose wire, but its running great.

I'm glad it worked out for you.

I thought about the Coolant Temp sensor being a potential contributor, but have not replaced it.


I did replace my ambient temp sensor, but that was AFTER the idle problem was resolved. I assume the ambient temp sensor plays no role in this.