Cold start problems '98 Explorer (HELP!!)

Hello all,

I got a bit of an issue with my '98 Explorer (4.0 SOHC). I'm driving it in the Netherlands by the way.

With temperatures dropping the cold start (when it's been about 12 hours after last driving it) isn't what it should be.

When I turn the key the engine starts immediatly and gives about 2000 RPM. Then it slowly drops to 300 - 500 RPM (at this point you can feel the car shaking). If it doesn't stall the above will repeat itself and eventually the idle will be more stable. After driving about a mile or so it runs fine (and I mean really fine, that's the frustrating part!). There is a small hole in the exhaust, but IMHO that shouldn't cause problems like this.

Remarkebly: One morning the Explorer showed the same problem and also after driving it for a few minutes the problem persisted and the car even stalled while driving (when driving up to a traffic light not using the accelerator pedal). I pulled over, turned of the ignition, took out the key (screaming my lungs out in frustration ) and waited a minute or so. Then I started the engine and everything was fine.

Off course me and my mechanic have been browsing the forum and we came up with a few things. This is what's been done up till now:

- the car's been hooked up to the computer and diagnosed by a dutch dealership that specializes in Ford USA: there were no trouble codes found. Next week the car will be diagnosed a second time by another dealer. Just to be absolutely sure.

- we ruled out leaky intake manifold gaskets (a common problem as I understand from the many threads on the forum) by spraying different parts of the engine excessively with brake-cleaning-fluid (with aceton). We did this when the engine was cold and when it was warmed up. The hoses were also checked manually and wre found to be in good condition.

- the MAF and IAC were thoroughly cleaned and tested. Both were pretty dirty.

- same for the EGR. It was clogged a bit with left overs of some fluid gasket. This was removed.

- the TPS was checked and apeared te be fine.

- the sparkplugs were replaced (two of them were bad).

- the ignition wires were replaced.

- the engine oil was replaced with the prescribed oil (5W30). First it was running in 10W40.

All this didn't solve the initial problem. It did however make the car run more smootly when the engine was warmed up .

Tommorow the ECT-sensor will be checked. I read that a bad sensor will also cause problems similar to the one I have.

Does anyone have any great ideas? I'm really stuck here !

Thanks in advance for the input!

ECT sensor & idle adjustment

Unless the engine coolant temperature (ECT) sensor is shorted it shouldn't affect engine cold start. A bad ECT sensor usually affects warm start because the PCM doesn't know the engine is warm and richens the fuel mixture assuming the engine is cold. The mixture will be excessively rich and the engine will run rough or die.

If your engine runs well after warmup I suggest that you perform the Idle adjustment procedure

I suspect that your IAC valve does not have enough range to adjust for the extreme cold. After performing the idle adjustment procedure your engine will idle (slower but not die) even if your IAC valve isn't functional.

ECT sensor & idle adjustment

Okay, tomorrow we'll check if the ECT-sensor is shorted (I assume you can check that with the multimeter?). If that's the case then replacing it would make all the difference. A bad sensor wouldn't normally affect cold start, if I understand you correctly. Wouldn't the shorted ECT-sensor give a code?

I'll also check the TPS again and suggest my mechanic to do the idle adjustment procedure. But that's just a temporary thing right? Just untill the IAC-valve is replaced?

Is there a way to determine if the IAC-valve is bad (except based on the rough idle at cold start)? I already unplugged the IAC-valve connector (engine was warmed up a bit) and it went from a stable idle to almost stalling.

And doesn't a bad IAC-valve also give a code when computer-diagnosing?

That's the thing that's not completely clear to me. Is it possible that certain abnormalities in a sensor are not 'extreme' enough to give a code but can in fact cause problems like the one I'm having?

But to leave on a positive note: I'm really looking forward to my upcoming May-vacation when we're taking the Ex on a roadtrip from Holland to France, Switzerland, Italy, Croatia and vice versa (over 2500 miles!). The Ex for me is the ultimate car for travelling long distances!.

But first I'm gonna tackle this problem!

Permanent idle adjustment

hansvdweerd said:

Okay, tomorrow we'll check if the ECT-sensor is shorted (I assume you can check that with the multimeter?). If that's the case then replacing it would make all the difference. A bad sensor wouldn't normally affect cold start, if I understand you correctly. Wouldn't the shorted ECT-sensor give a code?

Click to expand...

Yes, the PCM will detect either a shorted or open ECT sensor and set a DTC accordingly. That's another reason why I think your idle problem is not ECT related.

I'll also check the TPS again and suggest my mechanic to do the idle adjustment procedure. But that's just a temporary thing right? Just untill the IAC-valve is replaced?

Click to expand...

No, I suggest that the idle adjustment be permanent. The IAC valve is an electro-mechanical device that moves continuously at idle. It is exposed to moisture and particles that pass thru the air filter and is prone to failure. If you have performed the idle adjustment procedure then the idle speed without a functional IAC valve will decrease indicating the failure but will still be fast enough to prevent stalling.

Is there a way to determine if the IAC-valve is bad (except based on the rough idle at cold start)? I already unplugged the IAC-valve connector (engine was warmed up a bit) and it went from a stable idle to almost stalling.

And doesn't a bad IAC-valve also give a code when computer-diagnosing?

Click to expand...

The PCM will set a DTC if the idle speed is much greater or much less than that commanded. The codes will be set when you perform the idle adjustment procedure and will need to be cleared after the procedure is completed. However, the tolerance is excessively large. Disconnecting the IAC valve electrical connector will detect total failure but not test for adequate range for various environmental conditions.

That's the thing that's not completely clear to me. Is it possible that certain abnormalities in a sensor are not 'extreme' enough to give a code but can in fact cause problems like the one I'm having? . . .

Click to expand...

The sensors allow the fuel injection system to adjust for different environmental and engine conditions to meet fuel economy and pollution requirements. If the PCM tolerances for the sensors were too strict then the vehicle would be unreliable from an owner's standpoint.

Usefull tips

Thanks for the information! I'll post a reply shortly with the results.

Unless they have already been replaced with the updated parts, I'd all but guarantee that it's the lower intake manifold gaskets. Spraying a flammable gas around them isn't a reliable way to test for those gaskets leaking.

Adjusting the idle using the throttle stop screw on an electronically controlled engine is a band-aid that doesn't fix the root cause of the problem. There is no adjustment for the idle in the service manual, and there's a reason for that.

Back from the garage

Today I did the idle adjustment procedure and I must say that with the IAC-valve onhooked (engine warm) it already had a smooth idle of about 490 RPM. I turned it up just a little bit. If any adverse effects occur or if it makes no difference at all I will turn it down to the original position.

After reading 2000Streedrod's reply I decided not to mess with the ECT-sensor which BTW is located in a very difficult spot to reach!

I also did the checks with the voltmeter as described in the Haynes manual of the IAC-valve and checked for short circuits. The only thing was that I couldn't get the IAC-valve properly backprobed.

And Gijoecam, you're absolutely right about detecting a possible leak in the gaskets.

Next week the Ex will be computer diagnosed a second time. If no DTC's come up I'm considering replacing the intake manifold o-rings and possibly the IAC-valve.

Tonight will be a cold night in The Netherlands (about 20 F) so tomorrow morning I can check out the cold start.

I'll let y'all know how it works out!

Agree with gijoecam

If the warmed up engine idles at 490 rpm with the IAC valve disconnected then I agree with gijoecam that you probably have an intake leak. Check the short right angle hose at the base of the IAC valve that connects the IAC valve to the rigid tube going to the main intake tube. Many people overlook it because of the location. Also check the pcv inlet hose that connects the main intake tube to the passenger side valve cover port. My intake manifold leaks were mainly between the heads and the lower intake manifold. Also check the large O ring that seals where the EGR tube enters the upper intake manifold. There's a photo of it in Starting my 00M12 Installation

2000StreetRod said:

If the warmed up engine idles at 490 rpm with the IAC valve disconnected then I agree with gijoecam that you probably have an intake leak. Check the short right angle hose at the base of the IAC valve that connects the IAC valve to the rigid tube going to the main intake tube. Many people overlook it because of the location. Also check the pcv inlet hose that connects the main intake tube to the passenger side valve cover port. My intake manifold leaks were mainly between the heads and the lower intake manifold. Also check the large O ring that seals where the EGR tube enters the upper intake manifold. There's a photo of it in Starting my 00M12 Installation

Click to expand...

Having read your very detailed write-up I can say this is definitely not something I can do myself... But all relevant parts en sensors appearing to be in good order and no DTC's popping up, replacing the gaskets seems like the best thing to do.

It seems to me that the new gaskets are not that expensive (especially with the current Euro/Dollar exchange rates), but that the costs of labour might make this a pricy job...

Would it be safe to say that a skilled mechanic would have a full day's work (8 to 9 hours) for replacing the upper en lower intake manifold gaskets?

In my opinion, a skilled mechanic should only have about 2 hours worth of work if he milked it. When I did mine, it took about three days all together, but I also took my time and had to snap some pics in the process to ask a couple of questions, and broke an unrelated part in the process. Anyone that's done it before and has the tools handy should only need a couple hours at worst. There's definitely not a full days' work unless something goes horribly wrong.

gijoecam said:

In my opinion, a skilled mechanic should only have about 2 hours worth of work if he milked it. When I did mine, it took about three days all together, but I also took my time and had to snap some pics in the process to ask a couple of questions, and broke an unrelated part in the process. Anyone that's done it before and has the tools handy should only need a couple hours at worst. There's definitely not a full days' work unless something goes horribly wrong.

Click to expand...

+1........ 2 hours, 3 tops... and given the symptoms, it sounds extremely likely to be intake manifold gaskets to me as well.

Mirge said:

+1........ 2 hours, 3 tops... and given the symptoms, it sounds extremely likely to be intake manifold gaskets to me as well.

Click to expand...

Okay, well given that number of hours it shouldn't be as labour intensive as I thought!

Thanks to all of you for the information so far. When the problem is fixed I'll let you know!

Gasket replacement time

It took me about 10 hours to replace the gaskets and more than half of that time was spent cleaning carbon deposits off of the manifolds and head ports. Also, I spent time removing the ECT sensor and engine temperature sender in order to replace the front upper chain tensioner and oil restrictor. Having a wobble 1/4 inch extension of the right length would have saved me another 20 to 30 minutes. I have since purchased one for the next time when I change the timing chain guides. I estimate that a mechanic with the proper tools and experience could perform just the two gasket sets (upper and lower) replacements in about two hours but would charge for three. Being retired I have plenty of time to attempt tasks myself and there is really no impact if a task takes many times longer than planned.

Cold start after IAC adjustment procedure

hansvdweerd said:

......

Tonight will be a cold night in The Netherlands (about 20 F) so tomorrow morning I can check out the cold start.

I'll let y'all know how it works out!

Click to expand...

Well, today I can't say I'm all that disappointed in the Ex's cold start. It was a moderately cold night with light snow.

At startup I did have to use the gaspedal a few times, but when I drove of all was fine. The first 400 meters it did however gave about 1500 RPM without touching the gaspedal (this is too much IMO). But at the first traffic light the idle speed went down to about 1000 RPM and after a short drive the RPM at idle was about 750 RPM.

The dreaded stalling at the traffic light didn't occur, so that brought a smile to my face!

It seems like perhaps the IAC-valve needed a little help?

Monday a replacement IAC-valve will be ordered and installed. I didn't forget about the gaskets that are possibly leaking. That will be step two if this doesn't work.

Correct parts number for IAC-valve?

hansvdweerd said:

Monday a replacement IAC-valve will be ordered and installed. I didn't forget about the gaskets that are possibly leaking. That will be step two if this doesn't work.

Click to expand...

My mechanic called his trusted parts supplier for a price quote for an IAC-valve for my Ex.

And hold on to your hats: the supplier asked 250 euro's! That about $ 350,00!

I realize that shipping (delivery in 4 days to The Netherlands via UPS Worldwide Express) costs about $ 100,00. But still, a new IAC-valve as seen on Ebay costs about $80 - $ 100.

I put the order on hold and decided to look around for myself and order a part directly from the US. And here's my question:

Can somebody help me with finding the correct part number (OEM) of the IAC-valve that's used in my Ex? I read somewhere that the VIN number is used for this? This is because I need the OEM to order the correct part for my car.

hansvdweerd said:

My mechanic called his trusted parts supplier for a price quote for an IAC-valve for my Ex.

And hold on to your hats: the supplier asked 250 euro's! That about $ 350,00!

I realize that shipping (delivery in 4 days to The Netherlands via UPS Worldwide Express) costs about $ 100,00. But still, a new IAC-valve as seen on Ebay costs about $80 - $ 100.

I put the order on hold and decided to look around for myself and order a part directly from the US. And here's my question:

Can somebody help me with finding the correct part number (OEM) of the IAC-valve that's used in my Ex? I read somewhere that the VIN number is used for this? This is because I need the OEM to order the correct part for my car.

Click to expand...

When I bought a new IAC for my 98 Eddie Bauer... it was $70 USD approx.

Try going to www.autozone.com and putting your truck details in, and looking for an Idle Air Control Valve... don't forget the gasket.. that was only a couple bucks extra.

Vin e

For your SOHC V6 engine the eighth digit of the VIN is E. Don't get one for OHV V6 which is VIN X

How do you clean the IAC valve?

Cleaning the IAC valve

tyri77 said:

How do you clean the IAC valve?

Click to expand...

I found this link to be very usefull:

http://www.explorerforum.com/forums/showthread.php?t=84220

Found it!

2000StreetRod said:

For your SOHC V6 engine the eighth digit of the VIN is E. Don't get one for OHV V6 which is VIN X

Click to expand...

I found the correct part on usautoparts.com. They ship to Europe using Bongo (reducing te shipping costs considerably!).

Can't wait to put the part on!