Sluggish and horrible gas mileage

[Maroon]

Honestly, the engine management system on these car is so horrible that inexplicable changes in power and gas mileage are typical. I've been driving my car for 70,000 miles, and I've had power/mileage all over the map despite very consistent driving. My car has terrible power right now for absolutely no reason.

Are any of your brake calipers dragging? The only definitive causes of my power/mileage losses were when each of my front calipers started to drag. You would think a dragging caliper would be obvious when you're driving, but it isn't. Go for a drive using minimal braking, and then compare the temperature of each caliper by touching them. If one is much hotter than the other, then your caliper is sticking.

 

[Soundwave.]

ill try that but i just had my brakes changed recently and was told everything was all good. And as far as i can tell, when i do drive next to other cars with my windows open i do not hear anything that sounds like my brakes being applied or dragged.

 

[Maroon]

That's probably not it then.

 

[Soundwave.]

Poured a whole can of seafoam in and ran it till empty. New tank of regular gas and mpgs have returned but power is still iffy

 

[JesseM]

Did you do anything after putting the seafoam in your gas? I mean is it safe to do that and not change the oil afterwards?

 

[Soundwave.]

yeah its safe. I poured it in when the tank was almost empty so it burned up and then put new gas in.

 

[pcb]

Seafoam can also go in the oil and sucked up the brake booster vacuum line.

When you put it in the oil is when you want to do an oil change afterwards.

http://seafoamsales.com/

 

[Soundwave.]

So crap gas mileage and power is back. This time im pretty sure it has to do with the weather. Anyone have any idea on what it could be? Here in northern virginia the last 2 days were in the 60s and now its back to the 30s. Car is sluggish and gets horrible gas mileage. i got about 80 miles to a 1/4 tank when before i was getting around 100-105 miles a 1/4 tank. Also car idles really low and boggs a bit almost as if its going to shut off and then it doesn't. I just installed new plugs about 5 months ago and I threw in a bottle of bg 44K 2 refills ago and that did absolutely nothing. BTW, I'm not throwing any codes at all

 

[Maroon]

Rough idle is typically a symptom of the EGR being stuck closed after warm up. Replace it or try cleaning it.

Exhaust leaks can also cause a rough idle and low power. Do you have any exhaust leaks. Check your downpipe to manifold joint specifically. I have had that pipe crack and come loose multiple times. The engine runs much better once I fix it.

 

[Soundwave.]

No exhaust leaks from what i can hear. If EGR valve was stuck would it throw a code?

 

[hornsfan10609]

It may throw a CEL but don't rely on it. I have experienced misfires without any codes thrown. There are many good suggestions in this thread of what the problem could be.

 

[Soundwave.]

yeah and thats what keeps driving me nutts. I keep coming back and checking once i remove something from the list. No misfiring going on. GAH WHY IS THIS CAR SO DRAMATIC lol

Ill have to check the EGR valve once i get some free time. If it getting stuck closed, will cleaning it fix it or will i have to just buy a new one?

 

[Soundwave.]

Rough idle is typically a symptom of the EGR being stuck closed after warm up. Replace it or try cleaning it.

Exhaust leaks can also cause a rough idle and low power. Do you have any exhaust leaks. Check your downpipe to manifold joint specifically. I have had that pipe crack and come loose multiple times. The engine runs much better once I fix it.

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

 

[blakemallay]

Really do sound like coils tho, My car is doing the same thing but i know it is coils do to it runs on 2 cylinders sometimes... Btw my power is crap at this time and out of a tank of gas it last me 380 kms.

 

[Maroon]

Maybe rough wasn't the best word. An inconsistent idle is what a bad EGR causes.

 

[bpt323]

what are you guys getting for net average MPG?? my last tank was 23.8.......... needless to say im extremely unsatisfied.
I have a set of new plugs waiting to go in-and the brakes have been refreshed(all 4 corners). along with the front wheel bearings.
Does adding a header help/hurt these cars? i can't imagine the pre cat is doing a whole lot for MPG

 

[Soundwave.]

i normally get about 32mpg but lately its been so bad i dont even want to record it on fuelly lol

 

[pcb]

Keep in mind that mileage always drops in the winter. ( although perhaps not as much as you are experiencing )

Trips of less than 10 minutes during the winter use 50 percent more fuel.

 

[Soundwave.]

Maybe thats it then. My job is a mile from my house and my school is around 6 miles.

 

[seventystangfan]

+1 on coils and plugs. Also, make sure there is no water is the spark plug hole. When I had my Focus I washed the engine bay and got water down in those holes and it ran TERRIBLY after about 30 miles. Bad thing was that the "water" was the green cleaning solution and I thought I had a cracked head. Do the coils and wires, and make sure your NGKs are good.