My 1995 Nissan Altima idles rough when at a stop or slow speeds (low rpm). Is it an emmission problem? EGR valve or sensor? Knock sensor? vacuum issue?

ok so when its at o. do it run rough i think you should clean up your throttle body and your idle control valve the valve may be stuck and clean out your egr valve and the passage way in the pipe

might be the CAM & CRANK SENSORS ! HAVE YOU CHANGED YOU AIR & FUEL FILTERS LATELY ? DO SO IF YOU HAVEN'T. DID YOUR SERVICE ENGINE SOON LIGHT COME ON ? IF SO, GO TO AN AUTOPARTS STORE, HAVE THEM PULL OUT ANY TROUBLE CODES,FROM ECM, IF IT SAYS CAM SENSOR, REPLACE THE CRANK SENSOR AT SAME TIME ! ALSO, THE OXYGEN SENSOR PLAYS AN IMPORTANT ROLE, YOU MIGHT REPLACE IT ASWELL . ALWAYS KEEP FILTERS NEW, OIL CHANGED EVERY 3000 MILES.

Hi there:EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor (DPF). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc.

In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.

• Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's & DPFE voltage. There should be a noticable difference in RPM's with the EGR open
• Clean out the EGR valve and/or tubing to remove deposits
• Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
• Replace the DPFE sensor (with a good quality / OEM one)
• Replace the EGR valve

Hope this helps.

Do you own a professional type scanner ?
007 Idle Speed Problems Scan Data for Idle
009 Idle Speed Problems Scan Data for EGR

Hello,
The EGR solenoid is activated by the ECM at mid range speeds so if you are testing it at a idle it will not show voltage. The ECM grounds the solenoid to turn it on which supplies vacuum the source to the EGR valve.. To test the EGR solenoid unplug it and supply power to the terminals on the solenoid with jumper wires. Just apply power momentarily and listen for the click.Don't power it on for long as it will damage the solenoid if energized for long periods.If the solenoid is working check the EGR valve by connecting a piece of vacuum hose to it and applying vacuum to it. If you put your fingers under the edge of it you can feel the diaphragm moving as it opens and closes when applying and removing the vacuum. If don't have a vacuum pump tester you can do it easily with your mouth on the hose as it doesn't take much vacuum.If the EGR is stuck remove it and try cleaning the carbon out.If you can't free it up replace the EGR valve. If you need more help here is a site which provides diagnostic help with pictures.The also have the part availible for purchase at a very low price along with many more hard to find emission related parts. www.qualityresale.net

The distributer on this car is an optical laser and they can be a real problem as the car gets on.Try to find a low km one at the wreckers.You will have to time it in when you change it.This is where I would go it sounds like the problem I had and this solved it. Best of luck

Knock Sensor - is not an issue
O2 Sensor-just sees the condition of exhaust, during the stall & sets a code

I would look at the Idle Speed Motor, TPS Sensor,even vacuum leaks,Egr Valve.
Don't know your veh systems, Hope that helps some.

Here is the common cause of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

yes the alternator can send dirty ..too high...or too low a voltage to the system causing all sorts of gremlins.. test test

Check throtle position sensor... one section closes a set of contacts when you take your foot off the accelerator... this is sent back to the engine control computer which adjust the timing to insure the engine stays @ ~ 800 rpm. It's easy to set with just a simple multimeter...