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Old 09-19-2010, 08:09 PM   #1
SubaruImpreza_power
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Question rough idle on throttle when sitting

I have this rough running that only seems to happen more and more as the temp drops but here is the thing.. if you start the car up it will idle normal.. however say you need to leave quickly like a few seconds after you start it runs rough almost like the timing is pulled until you hit 2K OR.... if you sit and wait an extra 30 seconds you can leave and take off as normal.

the stuff below I copied and pasted from USMB but it would of been better if I had the camera in the car but on this past Saturday I exacerbated it by having to leave to follow a friend who's car I worked on.

Well after moving my car out of a friend's driveway and checking out another car I got back into my car and I had to quicky jump in and pull off.

I almost never do this by pulling off right away and never when it does that rough running when you give it gas.

Anyways I went to pull off and I had such a hard time getting over 2,000 rpms and after it did the car "opened up"

I can't think what on earth this is... I'm not sure what temp the oxygen sensor goes back into Open or closed loop but I was thinking of installing a A/F wideband just to see if it's running rich during that time.

It seems like the colder it seems to get the rougher it will run if giving it gas after started but it goes always always after a few seconds.

today would of been a perfect time to have a damn camera mounted in the car...


What I have checked is all the injectors to see if I had a leaking one (checked the ohm reading)

I replaced all sparkplugs and they while needed to be changed they looked good.

The funny thing about all of this is say starting the car back up like coming back from going in the store it's fine.. it's just the sitting for like 1 or 2 hours it will appear.
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Old 09-20-2010, 11:48 AM   #2
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Sounds like it could be the idle air control valve
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Old 09-20-2010, 11:54 AM   #3
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ICV or a vaccuum leak.

I would give it a smoketest to ensure you don't have an intake/vaccuum leak, and have someone check the Idle control valve.

You throwing any codes yet? Lean misfire codes would almost certainly confirm a vacuum leak....
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Old 09-20-2010, 12:05 PM   #4
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I've never got a code over this it for sure seems to get worst when it's colder..

and remember if I don't press the throttle after starting it you would never really know it was beside the faint funny idle sound.

This morning when I left for work around 4 this morning it was around 46F outside so as it was expected I jumped in and idled for about 20 seconds then backed out and went forward at that time whatever this issue was was going on.. so I decided to see what would happen if I tried to floor it to move the car.. it was sluggish until it reaches about 2800-2900 rpms and it shoots off.. and never happens again until the car sits for 30 min to overnight.

It's 66F out right now so when i head outside for a drive I'm going to bring the camera along.
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Old 09-20-2010, 12:56 PM   #5
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Hmmm...the fact that it doesn't happen after you are warmed up, until the car sits for a while...that may be an important diagnostic piece of info.

Can you put a multimeter on your coolant temp sensor to ensure its also working in the correct range?
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Old 09-20-2010, 12:59 PM   #6
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speaking about the coolant temp sensor I replaced that 4 weeks ago hoping that was it.. (I still have the old one in the box the new one came in) But replacing the CTS did nothing.
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Old 09-20-2010, 01:02 PM   #7
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Any issue like this and I check the usual suspects, just to cross them off the list:

MAF, clean and test it.
Precat O2 sensors
Check for vacuum leak
Plugs
Fuel pressure
ICV


OH! Have you tried unplugging your MAF to run in table/limp mode? Does that change the behavior of this issue?
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Old 09-20-2010, 01:09 PM   #8
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I have not unplugged the MAF to check that's a good Idea to test.

From the list you made I changed the plugs (have the picture around of the old) and fuel pressure I have not checked I do have pressure gauge.. which brings me to a question.. searching here some said about the fuel filter on the pump side that I have not checked but i changed the fuel filter under the hood last year.

ICV I cleaned with seafoam early this year I can't say it really helped but I did not remove it because I did not have the gasket.

02 sensors no code for them But remember this only happens on a cold motor so the ECU is still in open loop.
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Old 09-20-2010, 01:32 PM   #9
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Not O2 sensor, cross that off.
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Old 09-20-2010, 01:33 PM   #10
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wow I just came back from a drive I stalled by accident because the engine did not rev up fast enough at almost near full throttle when I went forward..

I exacerbated it so you can see it more clearly I never take off with full throttle on a cold motor not sure if the mic picked up the rough running under throttle.. seems to get wost the more open it is.

and yes when I restarted after I stalled I was at full throttle.

video best viewed at full screen can't really see it in the window mode.


Last edited by SubaruImpreza_power; 09-20-2010 at 01:46 PM.
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Old 09-20-2010, 03:49 PM   #11
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Yeah, I dunno, but I would want to see what my fuel pressure looked like, during that event.

If the pressure is fine, then you could look other places, but if its all over the place, then you would know something is up.

At least you could cross it off the list.

I'm amazed that running that rough didn't throw at least a few misfire codes or something....
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Old 09-20-2010, 03:52 PM   #12
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yeah it's crazy my code reader has live data.. for the fuel gauge it goes between the inlet to the fuel filter, no?
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Old 09-20-2010, 04:02 PM   #13
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On some cars there is a fuel pressure test spot....like a T on the fuel line that is just capped.

If not, then yes, I think pre-filter is how I've seen it done (I don't own a FPG but I have wanted one in the past).
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Old 09-20-2010, 04:33 PM   #14
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i would have to use the line to the fuel filter

What pressures should I be seeing?
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Old 09-22-2010, 04:39 PM   #15
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I just came back from pulling the MAF plug.. got all the normal stuff (CEL) so it idled a bit loppy so I decided to drive around the block ha a lady was nice enough to let me go in front of her and I went to give it gas and it did pretty much the same stuff that happens with the sensor plugged in..

Feels like I can make coffee by the time it gets to 2K.. and when it gets to 2K it opens up.

So faulty MAF? I mean it has a red and white sticker that says it's a reman.. only thing is I can't tell if it has a date or something on it..

Also is the temp gauge related to the MAF? I noticed it started to climb a bit when I started to pull off be the engine was hesitating But went down when the rpms started to climb.

is the MAF sensor it's self testable?

I have CRC QD Electronic Cleaner is that safe to use on the MAF?

Last edited by SubaruImpreza_power; 09-22-2010 at 04:46 PM.
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Old 09-22-2010, 04:46 PM   #16
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If you can find the specs, the MAF is semi-testable in terms of this: You can see if the voltage coming out is within the specified range.

The last time I did this on a car was a while ago, and the MAF just put out a voltage that corresponded to the amount of air/oxygen flow across the sensor.

If your MAF is the same, then you can sanity test it. If the MAF has a more advanced signal....such as a pulsewidth modulated signal or similar, then testing it will be a lot harder.

However, if you unplugged the MAF and STILL had the same results, then I think its safe to say the issue is not the MAF.
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Old 09-22-2010, 04:53 PM   #17
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my meter only shows what in lbs/ sec how much the MAF is metering..

Also I pulled the plug on the MAF when the engine was still warm this only happens when it's been sitting longer and it's for sure temp dependent... I parked out in the sun for 3 hours and I came back out and I started and no rough running when lightly on the throttle but as soon as the temp drops in the mid to low 40's that's when it shows the best.. Pulling the plug on the sensor when it was warm produced the same issues as if it was cold.

took the MAF out date says 4/4/01

Last edited by SubaruImpreza_power; 09-22-2010 at 05:29 PM.
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Old 09-24-2010, 07:30 PM   #18
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Does your car`s idle drop like mine when I do a warm start up?

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Old 09-24-2010, 07:33 PM   #19
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More updates.. I cleaned the IAC (fixed my crazy idle upon a warm start)

I also checked my fuel pressure.. I did a video of it but I forgot all about waiting like 5-10 min to see if the pressure held.. it might show in the video but it was dropping a bit.

Should it drop as soon as you turn the car off? the haynes manual says to wait 5 min and the specs listed said the hold pressure should be 30 psi but not that way for me.

from what I seen around it could be the fuel pump or the FPR or possible injector.. but I checked those back in the spring and they seemed to all test good (was still having the rough idle back then and last year)

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Old 09-24-2010, 07:35 PM   #20
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Quote:
Originally Posted by J-Chow View Post
Does your car`s idle drop like mine when I do a warm start up?

YouTube - 001.AVI

Mine did the same! I think I have a youtube video of it.. I took out my IAC and used half the can for that and the rest for the hoses.. it seemed to cure that issue because it's downright annoying..

I can let you know for sure when I come back from the food store.

Yeah here is the video I did back on Aug 28th 09


And my cleaning today


Last edited by SubaruImpreza_power; 09-24-2010 at 08:13 PM.
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Old 09-26-2010, 09:23 PM   #21
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Any takers on the fuel pressure?
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Old 09-26-2010, 11:40 PM   #22
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Shouldnt fuel pressure be at 3 bar (~43psi)? It should not drop that fast when off.
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Old 09-27-2010, 04:04 AM   #23
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no 30 psi with the engine idling the pressure should rise if the vacuum hose is disconnected from the FPR.
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