Sluggish and horrible gas mileage

yeah...... no thanks to the previous owner for this one...... (luckily i've only driven the car for 1 full tanks worth since buying it)
DEF- check your plugs

NGK's are in the car now. & a notably smoother rev-range

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More on this, The idle isnt rough as in I have a set of very aggressive cams but its more like it'll dip to around 500rpms and then go back to normal idle around 1000
I consider my car to run extremely well even though it occasionally does the exact same thing with a bouncing Idle.
After I disconnect the battery the ECU has to relearn the car and the idle is extremely rough for about 100 miles of driving.
I had the same sort of thing happen two days ago after the same weather conditions you experienced. It was really cold out after a week of warm weather and the car started normally and idled for about a minute then dropped to 500,.. bounced around for a few seconds then went back to about 1200 rpm.

I figure as the ECU learns the car, it uses that information at the next startup, and being is it was much colder out the switching point to start turning off the "choke" (reduce the idle on our fuel injected cars) was different and didn't "take", so the car waited longer before reducing the idle.
The ECU reacts instantly to some sensor data information but needs much more time to assess other data,.. let's see if my car "remembers" how to warm itself up next time I start it.
Your car may very well have more going on then just its normal quirkiness but if you're doing mainly short trips in this cold weather without the car really ever warming up fully, it's a good idea to give it a hard highway run for about half an hour every week or so.
( both my sisters phoned me to stay their engine light came on,... a half hour on the highway cleared the code both those times)

PS... proper idle is 720 rpm (when fully warmed up),... perhaps your car keeps trying to bring it down but it doesn't "take" (for whatever reason) so it needs to give up and go back to 1000,... then it tries again later.
 
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I consider my car to run extremely well even though it occasionally does the exact same thing with a bouncing Idle.
After I disconnect the battery the ECU has to relearn the car and the idle is extremely rough for about 100 miles of driving.
I had the same sort of thing happen two days ago after the same weather conditions you experienced. It was really cold out after a week of warm weather and the car started normally and idled for about a minute then dropped to 500,.. bounced around for a few seconds then went back to about 1200 rpm.

I figure as the ECU learns the car, it uses that information at the next startup, and being is it was much colder out the switching point to start turning off the "choke" (reduce the idle on our fuel injected cars) was different and didn't "take", so the car waited longer before reducing the idle.
The ECU reacts instantly to some sensor data information but needs much more time to assess other data,.. let's see if my car "remembers" how to warm itself up next time I start it.
Your car may very well have more going on then just its normal quirkiness but if you're doing mainly short trips in this cold weather without the car really ever warming up fully, it's a good idea to give it a hard highway run for about half an hour every week or so.
( both my sisters phoned me to stay their engine light came on,... a half hour on the highway cleared the code both those times)

PS... proper idle is 720 rpm (when fully warmed up),... perhaps your car keeps trying to bring it down but it doesn't "take" (for whatever reason) so it needs to give up and go back to 1000,... then it tries again later.

I normally let it sit for 5-10 minutes before driving. IF i can't give it that much time then i atleast wait 3 minutes before driving it VERY slowly (shifting at 2k rpms). One thing i did notice was, all this started happening after I had the battery terminal come loose. So im assuming the ecu is still learning.
 
That's most likely it then.

It's a good example of where if you ignore it it'll go away.
Even the crappy mileage if you can ignore that till spring.
 
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That's most likely it then.

It's a good example of where if you ignore it it'll go away.
Even the crappy mileage if you can ignore that till spring.

So poor gas mileage is especially noticeable in these cars then during the winter? During the summer i was getting 35mpg
 
So poor gas mileage is especially noticeable in these cars then during the winter? During the summer i was getting 35mpg

My gas mileage has gone way down the past couple of tanks. This is the only car I've had that gets worse mileage in the winter.

35mpg is exceptional mileage, and it sounds like you're falling into the normal range. From reading this board, most get about 25-28 mpg, and the lucky ones are at 30-31. I got 32mpg briefly when there was a gaping hole in the intake tube, and the car was running lean. It was nice, but started to cause problems.
 
On a full tank of gas I average about 360-380kms. I drive on the highway everyday to go to school about 30-40km a day highway driving. and I do daily city driving too. What can I do to improve mileage im planning on cleaning my EGR valve this weekend will this help. Car is stock except for a full injen cold air intake, and new ignition coils
 
On a full tank of gas I average about 360-380kms. I drive on the highway everyday to go to school about 30-40km a day highway driving. and I do daily city driving too. What can I do to improve mileage im planning on cleaning my EGR valve this weekend will this help. Car is stock except for a full injen cold air intake, and new ignition coils

the CIA is actually going to hurt you. The stock P5 intake is maximized to be the most efficient. You best bet would be to keep stock intake box and maybe just upgrade to bigger pipping. Cleaning your EGR will help as well and also fresh oil (depending on how long its been) and properly inflated tires.
 
i get anywhere from 26 to 34mpg average on a half to a full tank depending on how much i use the freeway or make short trips to get a drink or food. i got 40 mpg 1 time on average over 3/4th a tank 65% highway. having a manual helps if you have one go to neutral anytime you can coast to stop signs, red lights ect, the p5 can coast almost half a block from 30mph start without dropping below 25 on a fairly level road. i get from 360-400 miles to a tank 95% of the time occasionally a few less but never below 348ish
 
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last tank 90% highway miles was ~27.8mpg. im less then impressed.

Edit: this is after fresh plugs and installing a 4-2-1 header. a 4 mpg increase from that helps..... but come on!!! this car blows
 
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last tank 90% highway miles was ~27.8mpg. im less then impressed.

Edit: this is after fresh plugs and installing a 4-2-1 header. a 4 mpg increase from that helps..... but come on!!! this car blows

The usual culprits for reduced fuel economy are:
1. air filter
2. O2 sensor
3. ignition fault

I've listed those in the order of liklihood based on my experience with several different cars.
 
it has a K&N filter on the OEM intake system.
there are no codes. but its not always a smooth idle
 
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