Rough Idle

[GLittler]

Ok so here is the situation. My wife's 01 Altima gets about 20-22 MPG in the city which I think is pretty low for a 4 cylinder but I could be wrong. The main problem however is an extremly rough Idle, about 600-700 rpm. Initially i though that it wasn't get spark and misfiring so I replaced the plugs and wires and also the cap and Rotor but it still was rough. I took the car to Autozone to have the codes read and they pulled codes that were about the knock sensor, the mass airflow sensor, a misfire on cylinder 4, and lean exhaust if I remember corrctly. They said that it could be a bad MAF sensor. So i bought some MAF cleaner and cleaned it out but the car still Idles rough. I've tested compression and all four cylinders have about the same compression. I've thought that It could be the fuel injectors so I put some lucas engine injector cleaner in it for a few tanks but that doesn't seem to affect it in anyway. Part of me wants to say that it is something in the fuel system but I'm not sure if its the injectors or the regulator. Is there anyway to tell? or do you guys have any other ideas of what the problem could be

Thanks in advance for all your help

[nissandoc]

Spray some carb or brake cleaner around the #4 intake runner at idle, if the idle picks up then the intake gasket at the head is leaking. Common problem on these cars. Not a job for a novice or inexperienced tech.

[methodmix]

I agree with the nissandoc. Perform that check and let us know your results.

By the way, 20-22 MPG for pure city driving is about what you should be getting. Of course, this depends a lot on driving style, weather conditions (cold temps and wet/icy roads hurt your fuel economy), tire pressure (keep inflated to manufacturer recommended pressure), the length of your trip (shorter trips, such as less than 5 miles from start to finish, result in lower MPG), and traffic conditions (lot's of stop/go obviously produces low MPG).

[GLittler]

Ok, so I tested it and when I sprayed near the 4th cylinder (or maybe it was the first, I forget) the idle picked right up, but it wasn't near the intake gasket but the valve cover gasket. could it just be the valve cover gasket and not the intake?

[nissandoc]

#4 is on the drivers side of the engine. Just spraying in the general vacinity of an intake leak it will pick it up. This is a very common problem on this engine. Just make sure you get a technician that is familiar with this repair. It is not a job for a novice and I have seen some jackleg shops mess up peoples cars.

[nissandoc]

#4 cylinder is the one on the drivers side closest to the transmission. If you spray anywhere nere a vaccum leak it will pick it up. Not a job for a novice. Make sure you get an experienced technician.

[GLittler]

I've rebuilt the engine on my corsica so I'm pretty sure I can handle it, Is there anything special that I should know about pulling off the intake on this year of Altima?

[methodmix]

Hi GLitter, since this is a very common problem, your best bet is to start researching previous threads on this forum. I'm pretty sure I've come across at least 1 or 2 "how-to" tutorials on what and more importantly "what not" to do in regards to changing your intake manifold gasket. I've never done this myself, nor would I attempt to, but I do own a Haynes manual and I'm 99% sure that it provides the steps on how to successfully change this. The hardest part I remember reading about was actually scraping off the old gasket because you want to avoid scratching the soft aluminum that your gasket sits on. It's probably also best to wait until the engine is completely cool before starting the removal process.

In the end you'll probably save yourself like $400 in labor. Good luck!

[havenhill9]

I have a '96 Altima GXE that had the same rough idle problem. Spraying carb cleaner at the #4 intake picked up and smoothed out the idle. I debated doing it myself since I had 2 years of automotive school and have rebuilt engines, trans etc. After researching it and talking to knowledgeable mechanics, I paid someone else to do it. It costs me $400, but I also had another quote for $500 but shop around at reputable shops. They told me that it would take 4.5 hours, but they actually had it at the shop for 2 days because it was such a bear of a job. It runs a lot smoother now and doesn't die but is still a little rough. A code came up for the idle air control valve (~$145 at RockAuto.com), so you might want to look into that first. I also found a good procedure on the web that's a little more descriptive that the Haynes manual (which isn't bad) but I can't find the link now. Good luck if you try it yourself, but I wouldn't recommend it.