would these cause my bad gas milagfe? any way to tell if the are faulty?

No, more likley a bad O2 sensor or in
need of a tune-up, BTW you didn't mention
the engine you have

my bad sorry. 1.6L FI. i wasjust thinkin that cuz a friend told me it would cause rough idle. and at the start up it is really shaky

my bad sorry. 1.6L FI. i wasjust thinkin that cuz a friend told me it would cause rough idle. and at the start up it is really shaky

What are the RPM's at when you first start it? -usually your description tends to be the truck not kicking into cold-start high idle(around 1400/1500 rpm) Mine is doing this right now, but it's not rough for very long, only about 1 minute, but when the winter comes, I'm going to see problems, which is why I want to get it fixed soon. On my honda's, it's mostly been the coolant temp sensor to cause this, I haven't looked into the zooks though, maybe someone here knows.

its exactly that but rough for one minute at 1000RMP

my bad sorry. 1.6L FI.

Ya, I allready know that, what engine? 8V or 16V 

i think i'm half retarded most dayts lol 8V

You only got 1 injector on an 8V engine, I would
start with O2 sensor, and see, then work around
to the Cat and air/coolant temp sensors, make sure
the MAP sensor hose is connected and not leaking,
other than that the standard tune-up stuff, there isn't
much else on these that causes bad mileage, other
than huge tires 

BTW what are you calling bad mileage?  I only ever got
23 stock brand new on the freeway with an auto trans.

bad is liek 16. put 235s on her and it went from 14 to 16. go figure went up lol.. its a new o2 sensor so shouldn't be that, new plugs, wires, pvc valve all new fluids, anythign else i should look at?

Ya, the O2,  is the new one a Bosch
I've had trouble with them, OEM one lasted
like 15 years, I should of kept it.

Mileage up, ya, lower RPMs = better MPG

If the O2 turns out to be OK, I'd say the cat is plugged,
an emmissions check will verify it, if you can find a $25
place for just that, a new cat is $90 at Autozone, plus
welding in.

I'm getting 16+ MPG in my Chevy Truck, with the savings
on fuel these fixes could save $$ in a hurry

low and behold it is a BOSH lol. but thats what bumped it form 14 -16. as for the cat it shouldn't be. its  barnd new . whole exhaust is form down pipe back bout 4 months ago. any rexccomnedation on the kind of brand to get for an o2 sensor

Well a Nippondenso is OEM I think, you
could look for one of those, or pull a used
one out of the wrecking yard, find a Japanese
car, match your wires, 1, 3, or 5 wire sensor
and grab it.

your increase from 14 to 16 could be the exhaust
system, and the O2 could of been defective like
mine was out of the box   

Have you checked the valve lash and timing and done a compression test? What colour are the plugs running?

Hey Wildgoody
 I Changed my exhaust manifold and when I did that I put a new Bosch O2 sensor in, I get 20mpg though so what would tell me if it were not working right?

ineed to pick up a manual i think lol. i have no clue where to begin for the valve lash or do a compression test. but as for the timing will try that in the mornign seeing as you helped me on that one:) thanx Rhinoman