Yet... Another PO171, 174 code problems

[AppFire]

Hello, I am new to posting here but have been using this website for almost a month now. What a wealth of information. Anyways, I bought a 1999 explorer several weeks ago and have been using this website to get all the kinks solved. Its got the 4.0 OHV engine in it. Everything is going well except those darn codes. Po171 and Po174. I have checked for vac leaks and found none, and replaced the maf sensor. The explorer starts, idles and runs fine. No problems at all with how its operating. I can reset the computer and the cel stays off for around 15 to 20 miles then trips back on. I have looked and read everything I could find on this website concerning these codes and have tried and checked what others have done to corner the problem. Any other suggestions would be greatly appreciated. Also, as soon as I have the extra dough I will become a member here, its the least I can do to support such a great website. It has saved me hundreds of dollars so far...... Thanks to all and please give me any suggestions of links I can look at.

Chris

 

[Turdle]

Have you replaced the upper and lower intake manifold gasket?

 

[AppFire]

I have not done those yet. Are there a link showing how to do this on the 99 explorer? Thanks

Chris

 

[swetrid]

Upper intake gaskets are the most common cause.

 

[AppFire]

If its just the upper gasket, I am positive I can handle that. May try that next and see where it leads. If its still throwing the codes I will post it. Thanks again....

Chris