High Idle Question


#1

I have a 2001 Nissan Maxima with 97k. I bought it used and am unsure of the past vehicle history (other than a clean carfax). I had a used car service inspect it before I bought it and then I had my mechanic take a look at it after I bought it; both said everything looked fine. I bought the car in the winter and it ran fine then, but now during the summer, its behavior is a little different:



The car runs good, but when I’m in traffic, it idles around 1000 - 1200 RPM’s. The first time I saw this, I put the car into Neutral (still stopped in traffic) and the RPM’s jumped to 2500 - 3000 or so and remained there for awhile. Also, when in traffic, I have my foot on the break, but the car feels like it wants to lurch forward; it consistently idles around 1100 or so. I should also note that it doesn’t consistently do this; sometimes it idles at a normal RPM, but most of the time the idle is high. I see the same behavior with and without the A/C on.



I live in a big city and only really drive it when I leave town on weekends (mostly highway driving). I’ve had it for 6 months and I’ve only put about 3000 miles on it.



I don’t know much about cars and am concerned that this is a sign of bigger problems to come. Any thoughts or ideas on what’s going on and/or how I can fix it would be greatly appreciated.



Thank you for your time.


#2

Does this happen while you are using the AC?
There’s a thingy that ups the idle speed when the AC compressor is running (but not that much) so it might be defective.
Or it could simply de a defective IAC (Idle Air Control) - used to be the choke on carburetted engines. Either one your trusted mechanic should be able to fix easily.
Nice car, BTW.


#3

You may have a faulty TPS (Throttle Position Sensor).

A broken or loose TPS can cause intermittent burst of fuel from the injectors and an unstable idle because the PCM thinks the throttle is moving.


#4

There is a throttle stop screw on the throttle body. Some people mistakenly think its an idle adjustment screw, its not. If someone adjusted this screw in the winter for the cold temps, it may be keeping the idle high because it isn’t allowing the idle position switch to make, and keeps the computer from taking control of teh idle via the IAC.


#5

Also, this could be a vacuum leak. Check the vacuum hoses, and replace the PCV valve. This is cheap and easy to do.


#6

Update: My problem is gone! As it turns out, there was something wrong with the cruise control module that was giving the engine false readings (forgive me as I’m sure my terminology is incorrect). My mechanic asked me if I used Cruise Control and when I said “No” he told me not to worry about it (I never use Cruise Control). He said if it acted up again, he could just remove the whole module.

Thanks to everyone who posted their ideas for my problem.