Recently bought 01 Altima, unknown history, 90k mi, engine and trans strong and quiet. Runs routinely at 900-950 rpm, A/C on or off. Occasionally drops down to abt 650 rpm, idle is not rough. Had a similar prob. on a 96 Escort. Fixed w. new TPS after review of Haynes manual. My gut tells me this one is not that simple. Found too many other possibilities after a bunch of internet mining. Intake gasket leak?-----expensive labor. TPS?----$110, but Haynes says it needs to be set properly with a multimeter. Idle speed control valve and gasket?-----$175 + labor. MAF sensor?----didn't check pricing. Vacuum leak(s)? EGR valve? Note that the CEL has not come on so I don't know if the system is sending any codes. Since it has 90k mi I thought I would replace the O2 sensors as maintenance. I'm somewhat anti-dealer but do you think I should just take it in for a plug-in diagnostic? The other issue I have, as many others have written, is poor gas mileage. Just checked it and only got 21mpg.......and I'm an easy driving slow poke. So, with all these possibilities in mind, I need some expert opinions on a proper plan of attack ASAP. Don't want to just start throwing money and parts in it without some good reasoning. Thx----unk
Modified by unk at 11:43 AM 6/19/2007

Don't know if you have it figured out yet...but my 2001 Altima did the same thing...it ended up being a intake manifold gasket. To check it...with the car running, spray some carb cleaner on the manifold at each cylinder and listen for the motor to smooth out. Chances are it is #4 cylinder...Hope that helps.

how do you get the intake manifold off? My friend and i tried literally all day to take it out to replace the intake manifold gaskets cuz the #4 cylinder is leaking air, but we couldnt. It seemed as if something was holding it back, or there wasnt any room to remove it.

Dude...I paid to have it done...you don't want to tackle that job...

The dealer wanted $1000 to fix...I went to local import mechanic and they did it for$600...they worked on it for a good 6 hours.

Sorry I couldn't be more help.

these are common for intake manifold leaks. do as suggested and spray some carb cleaner or brake clean around the upper intake maniold to head gasket. they are a pain to replace but have done them at home in a garage over a weekend.