Pulsing Idle

Hey, So I got my car, (Subaru Impreza 2000 RS 2.5) and its has a pulsing Idle. I start my car cold, idles around 500 rpms (the normal) then once the car is warm, its starts to pulse. Always goes lower in rpms then corrects itself back to 500. But in the correction it never fully corrects itself so its always decreasing. Then the car dies. Only at stops. the car runs fine when driving. Except acceleration is rough. If I turn on my A/C, it almost keep the car alive. Only when the A/C is increasing the idle does the pulsing go away and no stall occurs. When the A/C is turned off the pulsing come back. On the low end of the pulse the dash lights dim.

I have checked the alternator and the test was positive. Reading around 14.3. I also had replaced the fuel injectors. Cleaned the o2 sensors and IAC valve. Checked the grounds. The wires plugs and coil pack are fairly new 10,000 miles. I have also cleaned the throttle body opening and my cars MAP sensor.

Can you please help me

Doe's this auto have a Massive Air flow, or meter near air filter box?

Doe's this auto have a Massive Air flow, or meter near air filter box?
Nope its MAP so it has no MAF sensor
MAP= manifold absolute pressure sensor

You may have a issue with the idle control valve. Does the service engine soon light come on?? Even if it doesn't have for ecu checked for codes. That should be you first step!

You may have a issue with the idle control valve. Does the service engine soon light come on?? Even if it doesn't have for ecu checked for codes. That should be you first step!

yeah no cel. i have a code reader too. everything looks good on it. I cleaned the IAC valve but yeah its a possibility its bad. i heard there is a way to use a voltmeter to check if the valve is good or bad but came up with random sites online in search for how to check the ohms output.

Anyone know how i might check this. There is 6 slots and I dont know what all of them are for on the wiring harness.

Sorry can't help you there, I have limited knowledge of Subaru's -- I did check the price on that part and was suprised that it's $350 aftermarket. Wow Not much to it either. If I had to bet money thats where your problem lies but it needs to be checked. I will see if I can find you any info...

Sorry can't help you there, I have limited knowledge of Subaru's -- I did check the price on that part and was suprised that it's $350 aftermarket. Wow Not much to it either. If I had to bet money thats where your problem lies but it needs to be checked. I will see if I can find you any info...


yeah the sensor has no meat on its bones what so ever. worth its wait in gold though. thanks for the help though! I checked online and there is a voltmeter test. I just dont know the setup for it.

the plug has six slots that look like this

- - -
- - -

and i only have a negative and positve lead ahhh

Hey try this site : http://forums.nasioc.com/forums/showthread.php?t=1311425

Hey try this site : http://forums.nasioc.com/forums/showthread.php?t=1311425

yeah thats funny cause my A/C on keeps the engine from stalling.
it almost gives it a boost from the jump in rpms.

im leaning toward a vacuum leak. which suck.
im gonna do the carb and choke cleaner method and spray that around the vacuum lines. see if there is a change in idle. You ever do this?

Yeah thats the best way to find a vacuum leak for sure, check around intake cause I would think that would be most likely. I still think that the ICV is most likely, once again not a subaru expert the a/c thing is odd, doesn't really make sense even with a vacuum leak. The computer will kick up the idle when the a/c is turned on of course so maybe it's able to kick it up enough even though the ICV is failing?? Not sure but is possible, eventually sooner or later I would think it will stall with the A/c on to.

Did that site help any??

Yeah thats the best way to find a vacuum leak for sure, check around intake cause I would think that would be most likely. I still think that the ICV is most likely, once again not a subaru expert the a/c thing is odd, doesn't really make sense even with a vacuum leak. The computer will kick up the idle when the a/c is turned on of course so maybe it's able to kick it up enough even though the ICV is failing?? Not sure but is possible, eventually sooner or later I would think it will stall with the A/c on to.

Did that site help any??

I'm actually a member on that site. haha
yeah the a/c thing is weird. as long as the a/c is boosting the idle it stays alive. the a/c will be on but the idle slows down cause the a/c not working so hard and the pulsing occurs again, but it kicks in again and the pulsing goes away. its one big cycle. The engine needs to warm up before any pulsing occurs as well. the first minute or two the engine purrs... If it was the IAC valve or a vacuum leak would the acting up occur right away?!

The ICV can work properly cold and as the engine warms up start to fail hot (eventually it will fail all the time). The vacuum leak depending on where it is should fail all the time. I have seen though vacuum leaks at the intake that show up after warmed up (expansion and contraction). So I would say that it still could be either or. Check for vac leaks it is easy to do as you already know. Eliminate that first and move to the ICV. I did a little reading last night and from would I have read the ICV is more likely you issue

The ICV can work properly cold and as the engine warms up start to fail hot (eventually it will fail all the time). The vacuum leak depending on where it is should fail all the time. I have seen though vacuum leaks at the intake that show up after warmed up (expansion and contraction). So I would say that it still could be either or. Check for vac leaks it is easy to do as you already know. Eliminate that first and move to the ICV. I did a little reading last night and from would I have read the ICV is more likely you issue

hey thanks for your help. really appreciate it. i started with the IAC valve and found a crack in the part the spring goes around. so i ordered a new one. I dont know if this crack is the problem, but the screw maybe able to turn free because of it.

i didnt get to check for vacuum leaks though. i am going to get this whole issue sorted out, so i can eliminate it all together. Then move on if the crack was not the problem

Sounds like you may have found the issue, let me know what the end result is! :rofl:

so i tested the iac valve and thats fine. drove the car too the grocery store and the cel came on. misfire on 1 2 3 4. The coilpack is new so i checked the wires and plugs and they have oil all over them. coming out of the spark plug holes.

same problems previously stated still exist


anyone?

Checked for vacuum leaks? Cleaned the throttle body? How are the O2 sensors? Make sure the PCV hose next to the throttle body on the passenger side isn't damaged, it goes down to the block and that thing gets rock hard and will crack.