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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 34442
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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Ford Explorer Sport: I have a 1999 Ford Explorer 4.0L SOHC

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I have a 1999 Ford Explorer 4.0L SOHC motor with 115k miles on it. Only issue is it will not idle when cold. I have to keep my foot on the gas for about 5 minutes until it warms up and then it runs fine. There are no codes or check engine light. I have read about the upper and lower plenum intake o ring gaskets going bad. You think this is the problem? If so are these gaskets only available from Ford or can you pick them up at the parts store and are they easy enough to replace. Or is there something else I should look at. Thanks, Ed
Hello and Welcome to Justanswer,

My name is XXXXX XXXXX I am here to try and assist your with your question.

The upper intake gasket are a known concern on your 4.0 but in most cases if its leaking it will set and store the lean codes P0171 and P0174. if you not getting any fault codes its not likely you need to replace the gasket set as of yet. The problem you are describing sound more like your IAC (idle air control valve is sticking due to be dirt and sludged up. Before doing anything else try removing it and cleaning it real well with some carb cleaner and while there also take a soft cloth and or tooth brush and clean the throttle body bore and throttle body plate. Once you have don't this, remove the negative battery cable for about 10 minutes to reset the PCM (computer).

The IAC mounts to the throttle body and is held on with 2 8mm bolts.

Customer: replied 5 years ago.
Thanks for the great answer. I am guessing it is the IAC as the throttle is a little sticky when cold (like you have to press on the gas pedal a little hard to). I had Ford dealer clean it a few years ago and the throttle was just fine then ( as far as the sticky). If it is the gaskets are the dealer item and are they are to do. I am pretty good garage mechanic.
Yes the dealer is the best place to get them and its not usually the lower intake but instead the upper and the revised gasket comes with new isolator bots as well. Its not to bad of a job and I can send you complete instructions if you need them. Let me have the 8th letter of your vin so I send the correct ones.
Ron and other Ford Specialists are ready to help you
Can I get the 8th letter in you vin number please?

Here are instructions for the SOHC 4.0. Let me know if you need more information. Click the link below and hit download.

Customer: replied 5 years ago.
Ron i worked on the Explorer last night and cleaned up the IAC and the Throttle body plate. It nows idles great when cold or hot and the gas pedal no longer sticks. Thanks again.Ed
Your very welcome and thank you as well. Great to know you got it fixed.