So I put a K-Spec (just a cheap $50 intake from ebay) cold air intake on my 01 tib last week. It sounds great and seems to pick up quicker, but I just filled up and only got 25mpg. I usually get 29. Same style driving (90% highway, never too hard on it). And my revs take forever to get back down to idle. Like if I'm coasting and pull it out of gear, the RPM's will stay at 1500 all the way until I come to a complete stop, and then about 5 seconds later after stopping they finally go down to 900 RPM or so.



What the heck would cause this? I was very careful with the IACV and the MAF sensors, I didn't touch them or clean or anything. And they're installed in the same locations in the intake. I did clean up the throttle body a bit since it was coated in oil. Would that have hurt anything since I was moving the TB valve back and forth a bit? Is there any way I can check the IACV and MAF to make sure they are operating properly? Thanks all!

 

Mine does this too.

 

post a picture of your intake setup. Interested to see the MAF.



Make sure the arrow is pointing in the direction of air flow.

 

My setup looks exactly the same as this pic attached. Same locations for both sensors and hoses. The MAF is mounted correctly, arrow pointing back towards the intake manifold. So it's normal for the idle to stay at 1500rpm until ~5 seconds after being stopped?



Even if I'm inching forward at 1-5 mile/hour not in gear, it will never drop idle below 1500rpm. Maybe I just never noticed it before with my stock setup.

 

The rpms should stay up for a lil while till you make a complete stop but I don't think for that long after stopping.



Check for intake leaks



Clean your iacv

 

what brand is your TPS? Dae Sung or Keifco?



Dae Sung is known to go bad.

 

is this the first tank you put through it since the mod?



it takes a sec for the ecu to adjust



id take a average of 3 tanks to see if there really is a prob, there is tons of variables that can alter mpg

 

I would do a ecu reset but on the theory of getting slightly more air flow the ecu will probably increase fuel.....

 

If you don't remember, it only takes a few minutes to put the stock setup back on. Go and give it a try.

 

This. But all of my hyundais have had that stupid 1500 rpm rev hang debacle - it's an emissions-reducing technique that can be defeated with an IACV restrictor plate. No biggie.