Car stalls at idle

[slantedmike]

A long story here, so I'll try to make it brief:

About a year ago my car started stalling at idle. The car threw a code saying it was running lean which most people said was a MAF sensor going bad. Cleaned it and it ran well for another 2k or so and then acted back up again. Replaced the MAF with a Napa one for about $220. That lasted for about a year and gave the same symptoms.

Took car to dealer (I know, big mistake). They said ECU and $900 later, the car ran the same. Bought cheap MAF off eBay for $40 and car still stalls at idle. Car runs rich now, plugs and O2 sensor are fouled. If I clean the plugs, car seems to run well for about 10 minutes until the symptoms return.

Any thoughts? So far I've cleaned the injectors, throttle body, idle air intake valve, and tested the intake air temperature sensor.

[boyrs]

Index of /FSM/Sentra

how is the battery and alternator? MAF & o2 sensors use voltage to report to ECM. what caused the MAF to get dirty? it'd most likely be the filter or back up of the gases from the EGR. is the car throwing any other codes? do you have the 2.5L or a 1.8L? any engine mods?

[slantedmike]

Originally Posted by boyrs

Index of /FSM/Sentra

how is the battery and alternator? MAF & o2 sensors use voltage to report to ECM. what caused the MAF to get dirty? it'd most likely be the filter or back up of the gases from the EGR. is the car throwing any other codes? do you have the 2.5L or a 1.8L? any engine mods?

Thanks for the response. I have the 1.8L with no mods.

The battery is from 2007. I haven't had it tested or the alternator. I might run by advanced auto and have them do that....maybe even clean off the terminals although there's not visible corrosion.

I change the air filter pretty regularly. The car has 140k and I bought it with 40k and I always change the filter before it's due.

The factory service manual says that the EGR is supposed to be closed at idle. So I don't know how that would effect the car, or if it would cause it to run rich. I know if I take the cover off and force it open the car stalls immediately.

Also, the code is not throwing any codes. I know it's running rich from the exhaust, fouled plugs, and worthless dealership's report. It's not enough to throw a code however.

[slantedmike]

I created a vacuum leak by pulling a vacuum hose off and the engine seemed to idle a lot better. More air makes it run less rich? Does that mean the MAF is not properly monitoring the air volume correctly?

[boyrs]

try unplugging the MAF and see if it idles fine for few minutes before it stalls, without a MAF connected, the ECM should put the engine into a limp mode and make it where you can't rev over 1.5K RPMs.

[slantedmike]

Originally Posted by boyrs

try unplugging the MAF and see if it idles fine for few minutes before it stalls, without a MAF connected, the ECM should put the engine into a limp mode and make it where you can't rev over 1.5K RPMs.

I've tried that multiple times. Every time except for once, the car stalled immediately. The one time it didn't, it ran rock solid.

My big question is why doesn't the system throw a code when it runs rough? Same thing for when I create a vacuum leak - no code.

[soty453]

I think if the ECU can compensate for whatever drivability prob the car is having, it won't set a code. Although, other times, it still will. Sometimes you get lucky though, and it will. Does your car run cooler than usual by any chance? I know that if the thermostat gets stuck open, it will stay in "open loop" and dump lots of fuel in the engine. The ECU tells the fuel system to go into open loop based on temp readings from the temp sensor. If it sees that it's cool, then it'll dump fuel in it to try to warm it up.

[slantedmike]

Originally Posted by soty453

I think if the ECU can compensate for whatever drivability prob the car is having, it won't set a code. Although, other times, it still will. Sometimes you get lucky though, and it will. Does your car run cooler than usual by any chance? I know that if the thermostat gets stuck open, it will stay in "open loop" and dump lots of fuel in the engine. The ECU tells the fuel system to go into open loop based on temp readings from the temp sensor. If it sees that it's cool, then it'll dump fuel in it to try to warm it up.

The engine temp appears to be normal. The car warms up normally as well.

As a side note that may be unrelated: A few times over the past week, as I slow to a stop, the break feel like the 'power' portion no longer works. As I start driving again they feel fine again. Air in the lines or something having to do with my idle problem?