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Hey all! New to the forum. I own a 2003 Subaru Impreza 2.5 RS with 210k miles on it. I bought it used at 207k miles. I do have an extended warranty and have it going into the dealership for repair come a week (backed up due to holidays). 

Here's a history of issues. About 2-3 months back it started having idle issues to the point where RPM will dip to 100 and then steadily toggle itself back up to about 1k. It isn't all the time but when it acts up it stutters. Not every drive does it do this. Anywhom I checked spark plugs and spark plug wires, they look to be in working order and do not need replacement (from my limited experience). The check engine light coded out for 02 sensor and a cylinder 1 and 2 misfire. 

More recently I was on the highway driving and it would not accelerate up past 70-80 MPH in 5th gear. Check engine light was flashing, indicating a misfire issue. It would continue to accelerate and function in 2nd, 3rd and 4th gear. When I got it to a stop light off the highway it died twice. I was able to drive it home without issue after I let the car sit. It idles well for the most part until the mercurial issue arises. 


Upon doing some research it occurred to me it might be the MAF sensor. My understanding is the MAF sensor can be cleaned and it might be the issue. I've searched around and tried to locate it, I have pictures of my most recent attempt to find it and clean it in an effort to keep the car running until my appointment and have a driveable car. 

Here are the pictures of what I thought I found to be the MAF sensor. From all that I've seen online this isn't the MAF sensor. Where would I find the MAF sensor on this specific model, and from what I'm experiencing does it seem to be an MAF sensor issue? 

Would appreciate any thoughts and input. 

Thanks :), this is my first post and hope to learn more about my car and maintenance it well. Love this car in the short 3000 miles I've driven it. 

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I think that is the Throttle Position Sensor.  I believe your car may have a MAP (Manifold Absolute Pressure) sensor located on passenger side front strut tower

 

92481d1405295594-so-i-keep-getting-map-s

Edited by Mike104

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Your can does not have a MAF, it is a MAP engine. That's the last picture you unplugged on top of the throttle body.

 

Long Long ago on MY04 Forester 5 speed I had something similar. Cold the engine ran flawlessly. After it warmed up, I had idle and misfire problems. My problem turned out to be the electronically controlled EGR. IF you have an EGR, it will be just to the right of the throttle body as you stand in front of he car ( drivers side).

 

After so many miles, carbon builds up and when they open, they STICK and don't close. 

 

Check and see IF you have an EGR.

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Needs NGK plugs and NGK wires first. Just because they "look ok" doesn't mean they're not the problem. If they're old, replace them.

Are the boots of the plug wires covered in oil? If so it needs valve cover gaskets as well.

 

You messed with the TPS it's going to need readjustment. Need a digital voltmeter to check voltage on the center wire. At closed throttle adjust so it shows 0.50 volts.

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Hey! So status update. I took it to the dealership, after they identified fifty odd things and presented me a $4000 dollar parts list I took it home. There were a number of things in relation to suspension but for the idle issue they had a few ideas. They started with a carbon flush which didn't clear up the problem. After that a code read out for the IAC sensor. I was told my aftermarket exhaust had been installed poorly and was missing bolts, I checked myself and there was only one bolt missing that I could find. It started to idle a little better post carbon flush but it didn't fix the issue. 

I pulled the IAC sensor, it looks clean. I did replace spark plugs and wires just to ensure they aren't part of the underlying issue. The car is still failing to maintain pressure after acceleration and RPMs dip or the car dies. The codes it's reading out presently are 
P0301 Cylinder 1 misfire

P0302 Cylinder 2 misfire

P0304 Cylinder 4 misfire 

P0037 Heated oxygen sensor heater control circuit low 

P0519 Idle air control system performance 

My understanding is P0519 can indicate a few problems including dirty IAC sensor or vacuum leak issues. I have someone coming out next weekend to test for vacuum leaks in the engine and he also wants to look at the EGR sensor. 

Any thoughts? 

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You need to disassemble the IAC and clean it. Happens all the time with these. 

 

Replace the plugs and wires with NGK (both). Appearances mean nothing. This is a normal tune up maintenance item. Just replace them or you may be chasing your tail. 

 

GD

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That's fair. I did do wires and plugs on Sunday, no dice. Going to disassemble and clean IAC as next step. Thanks!

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Forgot to mention as well that I did remove IAC sensor, the carbon flush they did resulted in the sensor looking clean. There's no carbon build up on it to speak of. 

A friend is coming out this weekend and we're going to check for vacuum leaks in addition to checking the EGR valve as a next step. 

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You need to readjust the TPS first. If that's out of adjustment the ECU wont set idle speed properly and will set a code for it.

 

The idle valves on those are known for failure and can cause idle problems like what you have, but even with a new valve you still need to properly adjust the TPS first or you'll still have idle problems.

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Hey, update! 

I replaced TPS sensor (checked voltage, adjusted accordingly) and the IAC valve. After which the car is continuing to have it's misfires and RPM dips. It'll dip to the point of killing the engine here and there. Since there's also a code for the rear 02 sensor I've ordered that part to swap it out. I have cleaned and checked grounds, replaced spark plugs/wires. Mind you after all of these things the car is idling better, however it continues to have episodes where idle is rough and killing engine.

My understanding is the dealership that sold me the car did swap the front 02 sensor but not the back 02 sensor. Since downstream sensor is still one of the codes being read I figure switching it out couldn't hurt. At this point I'm hoping this rear 02 sensor might put an end to it. Is it possible the computer needs to be reset to relearn the new TPS sensor? 

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A thought occurred to me as well, maybe it'd be useless to replace rear 02 sensor due to the exhaust being aftermarket? since it's not factory exhaust it's going to probably trip the 02 sensor regardless. Is it possible I didn't adjust the TPS properly? 

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In your 2nd pic, the item behind the one held in your hand, that is the Manifold Absolute Pressure sensor or MAP (not MAF)

 

they seldom fail, but it is a possible source of trouble.  At least check around it and all of the intake manifold for air leaks.

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I think that is the Throttle Position Sensor.  I believe your car may have a MAP (Manifold Absolute Pressure) sensor located on passenger side front strut tower

 

92481d1405295594-so-i-keep-getting-map-s

 OPs car in this thread would not have this MAP setup.. his is on the top of the intake.

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With all 4 cylinder misfires, and bad idle..... I still say IF you have an EGR, it MAY BE STICKING OPEN.

 

When you start the car cold..... the EGR is not used..... AFTER warmup, the EGR functions. and THIS is when I had the BAD IDLE.

 

I have seen this on Foresters and Outbacks..... after MAY a dealer handed the owner many bills and not fixing the problem,

 

Especially on the electronic EGR. It has a stepper motor that pushes DOWN on the EGR plunger. but when the stepper returns, Electronically the ECM thinks it returned as the stepper motor DID. But the plunger with carbon built up on it does NOT , sticks open even at idle, and causes the  low looping idle,,,,, and bad bad exhaust smell.

 

http://www.subaruforester.org/vbulletin/f88/low-idle-stuttering-erratic-jerking-various-rpms-76450/index3.html#post887065

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Did check for leaks, will do so again tomorrow. I'm running out of guesses here. It does reek of exhaust whenever the idle dips. In idle car struggles to resume idle after dips (but stays running)

 

Car does not run an egr. I'm thinking MAP sensor may be the culprit.

 

I also checked accelerator cable, there's no issues with the tension or response that I've noticed.

 

I neglected to check coil packs, will be doing that tomorrow just in case.

 

I also ordered an odb2 Bluetooth adaptor that gets here on Thursday. Will be using it with the app torque to clear codes and retrigger to see if any new indicators from ecu can be gleaned. I'm hoping to get enough information to solidly diagnose without throwing anymore money at unneeded parts.

 

Appreciate all and any suggestions to point me in the right direction and aim to have better information to present on Friday after odb2 readout

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Intermittent low-idle/stalling could also be due to:

- Idle Air Control Valve. The IACV can be cleaned to remove excess carbon; or

- Crankshaft Position Sensor (on its way to dying completely); or

- Camshaft Position Sensor.

Do you get the low-idle when going over bumps & potholes?

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GeneralDisorder, the cable was loose. Really good thing to check though hadn't thought about that.

 

Forester2002s I haven't noticed issues while going over bumps. At any point engine has to maintain idle after warmed up i.e stationary or engaging clutch while driving.

I did replace iac valve. Would camshaft or crankshaft position sensors read out a code?

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Crankshaft Position Sensor: P0335

Camshaft Position Sensor: P0340; P0341

 

Faults can be due to a failing sensor OR to failing wire-insulation.

If you get one of the codes, give the wiring and connections a good shaking and push-pull; sometimes this helps to either clear the fault, or to exacerbate the problem. Either way, this helps with diagnostics.

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GeneralDisorder, the cable was loose. Really good thing to check though hadn't thought about that.

 

Forester2002s I haven't noticed issues while going over bumps. At any point engine has to maintain idle after warmed up i.e stationary or engaging clutch while driving.

I did replace iac valve. Would camshaft or crankshaft position sensors read out a code?

 

nuetral switch on side of trans?  Not closing to tell the ECU you are in nuetral?

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Thanks to all for making suggestions. I appreciate you all letting me comb your brains. on that note, not done yet! lol
I'm having misfires on all 4 cylinders and a downstream 02 sensor code yet.

So,I took it into a shop. They spent 2 1/2 hours diagnostically and couldn't find the underlying issue. Cleaned the Throttle intake somemore, has been done. What was mentioned however was the faulty wiring on the downstream O2 sensor. I just jacked the car up and discovered that the connector was spliced. There's no plug anymore, with that in mind the new downstream 02 sensor I have needs to be spliced into the system. There's a problem though, the wiring on my new 02 sensor has 2 white wires, a black wire and a gray wire. The old 02 sensor has 2 black wires, a blue wire and a white wire. I havn't been able to find any wiring diagrams that indicate voltage on the 02 sensor wiring that would help me figure out which wire would go where...I'm kind of at a loss here. I'm wondering if they jacked the wiring on the 02 sensor and it's sending rump roast backwards readings to the ECU that's causing it to remain in open loop?
 

 

nuetral switch on side of trans?  Not closing to tell the ECU you are in nuetral?

This is a really good point and I need to check that out. I havn't had any codes read out for it but it's as good a supposition as any.

Edited by Syncert

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