Hey guys i've searched for this, and found alot of Info, but I still cant seem to solve my problem. My explorer starts normally, and drives fine. The problem is that during a cold start up the truck fires right up and slowly creeps down to the normal idle speed. Then she stumbles down to like the 400-500 rpm range and almost dies out, but right before I think its going to die It idles back up to about 2000 rpms. The engine will slowly come back down to normal Idle speed, again, and then the same thing happens,down real low before rocketing back up. It will do this for about ten minutes after a cold start up. Ive gone through everything basic and somewhat advanced that I can think of. This problem seems to go along with the colder temps this time of year. Ive tested quite a few things and have found nothing. The explorer drives bueatifully, has great power and acceleration. Ill try to list everything Ive done so far but if you can think of anything else, ask because I may have forgot to put it here. Any help or other suggestions are greatly appreciated.

1998 explorer 4.0 sohc automatic 4x4
198,852 mile on the clock
Things changed at 195,000
-plugs, used autolight app103 I believe
-wires, motorcraft brand
-fuel filter, wix brand
-air filter, wix as well
-IAC, standard motor company brand
-thermostat, stant brand, oe temp
-lucas fuel conditioner was added to the tank

A few other things were done at this time, changed the belt, and installed new ball joints and tie rod ends, along with shocks.

The truck exhibits no problems other than the idle speed problem, no driveability, and no cel. I had the throttle body replaced for the tsb a while back. Ive checked and cleaned the the mass air flow sensor, I cleaned It with CRC mass air flow sensor cleaner. The fuel pressure is fine, about 36 psi at Idle and holds steady when being driven, the pressure goes up when the regulator line is disconnected. Checked the vacuum at idle and its about 16-18 in with a steady needle, I tried the propane and carburetor cleaner on all parts of the intake just to completly rule that out, and the idle speed does not change. Checked and cleaned the throttle body bore. Compression tests even across the board, I believe it was about 160 psi. Like I said I changed the IAC and it kinda helped for a while, maybe 2 weeks, then It got alot colder here. The old IAC was clean inside and the solenoid ohm'd out fine. Ive gone over all sensor connections and found no corrosion, damage or loose ones. None of the vacuum lines are cracked or leaking, including the crankcase hoses. The engine does not leak oil or use any either. Just to check I applied vacuum to the egr valve and the engine died. All of the fluids are fine. This problem is unaffected by ac operation or brake pedal application. Like I said theres no CEL which automatically made me think of the IAC, but my problem still exists. Ive gone over all the engine checking for vacuum leaks, and can find none. I Think Im looking over something simple here, Ive tested and checked some other things as well that probably dont have any contribution to my problem. This morning It was like 6 degrees and the problem occured right away of course. Ive tried gas from 5 different stations and that seems to have no affect, Ive also tried seafoam, through the gas tank and through the intake but to no avail. I dont believe in changing parts to try and solve a problem, and refuse to unless i have a good reason. I also confirmed that there are no codes with a scanner, and that I dont have a burnt out CEL bulb. The AC compressor was changed about 35,000 miles ago by ford, and I installed a new alternator and battery around the same time. Im sure im missing something here.

 

Could be an intake gasket. Those gaskets shrink and expand with the temperature. You could have a small break in the gasket and when the engine heats up, it swells enough to close the gap.

When it's cold and exhibiting the surging condition, try spraying some starting fluid around the gasket. If the idle goes up, you've found your problem.

Also, have you checked the MAF?(mass air flow sensor) Here's a link for that.

http://www.explorerforum.com/Singlet...ages/ping.html

 

I agree, the intake manifolds on these leak often, and they may exhibit different behaviors at different temperatures.