2001 nissan sentra 1.8 gxe,140,000 miles auto trans.

[quote:ddb086cb23="joezepe82"]my sentra gets very bad gas milage, the car shakes when idling, and has a slow take off speed, ive changed the O2 sensor, and it worked for a while now its back to the same problems, some one told me it could be the intake manifold, im on a budget and a manifold is not in it. please give advise. thanks.[/quote:ddb086cb23]

Hello !!
is the "check engine light" On?
start checking the EGR and remove the carbon build up (could be stuck open)also check the IAC sensor (Idle Air Control valve) remove it and clean the gum and varnish out of it.

let us know to continue..

the check engine light is on and the egr valve is poped open. how do i close it? 8)

[quote:7bbb5ec290="joezepe82"]the check engine light is on and the egr valve is poped open. how do i close it? 8)[/quote:7bbb5ec290]

Hello !!

remove it and clean the carbon build-up ..
also check the "codes" (should show a EGR issue..

here`s how:

https://www.2carpros.com/dia/index.htm

let us know which codes you get !