my 98 with 4.0 motor on a cold start will jump the rpms to about 2100 then if you don't catch it with the gas pedal it will die. It will run up and down from about 2100 to 500 if you play with the gas pedal and keep it running. After it warms up for about 3-4 minutes it will run fine. What can I check?

thanks
JIm

 

I had the same problem on the same truck a few years back. If memory serves it was a headgassget or something similar. It is an issue Ford knows about on the 98/4.0 SOHCs. There was an official "campaign" for this issue, which I THINK means you don't have to pay for it.....

 

I just found more specific info. Here is a quote I pulled from another post.

"your engine codes (P0171 and 74) are probably caused by a leaking lower intake manifold gasket. The PCM will register lean because of the extra air that is beening drawn into the intake. You can contact Ford and get kit to fix the problem, just tell them you need a kit for the ford explorer sohc 00m12 recall (program actually). The cost is $45 - $55 depending on where you live. If your explorer has less than 72,000 miles ford will complete the entire job free. I just finished this fix on mine, and it runs better than it ever had; took me about 4 hours but I was b/s'ing with the neighbor more than working on the engine. Also you can check your spark plugs and wires to make sure the wires aren't cracked and the engine hasn't fouled the plugs while trying to start in the cold. "