Syncert

I did adjust the TPS correctly. Intake was pulled, there isn't any build up or sludge affecting injectors. Plugs are a consideration, didn't realize double iridium could cause those issues with idle. IAC and associated hoses have been checked. MAP sensor was swapped with functioning one to verify, no difference. Grounds have been checked. Neutral switch was checked and verified to be signalling correctly. Fuel trims are indicating the engine running rich at idle otherwise it's running normally. The problem is idle trims and maintaining idle. It's sooting up plugs and chugging fuel at that point. After engine warms up Tachyometer drops to near 0 when it surges then it eventually regains 700 rpm or dies. What I'm gathering from this is the injectors are a very real possibility. Spark plugs are something to be addressed, and that rear O2 sensor is not a negligible factor. Correct?

Plugs and wires are both NGK. The NGK double iridiums I threw in were sooted up by the time they were yanked again to check them 2 weeks later due to how rich the engine is running in idle. Otherwise it drives fine. This weekend I drove it and it stalled out at stoplights throwing misfire codes. Timing cover was pulled and timing is correct. Last ditch theory is the fuel injector is shot and that's going to be swapped next. Otherwise we can't think of anything else.

Status update! Since the last post I did take it into a mechanic. He has a subaru master tech certification. In the past week that it's been in the shop there's been a number of diagnostics ran. We both have our hands up in the air saying what the codswallop, as such he's going to consult other techs he knows to see if we can divulge. I decided I can also help by consulting on forums. The engine is running rich. Codes presenting are still misfire codes and rear O2 sensor. In terms of driveability I've taken the car back for the weekend, cleared ECU to try to get additional codes. Driving the car it runs fine unless it's trying to idle. When the engine is warmed up it stalls out at idle. To keep it from dying have to rev the engine at stop lights. Here's what's been additionally done and diagnosed at this point. -Timing. All timing has been looked at except for removing passenger side timing cover and determining if it's skipped ahead a little bit. -Fuel pressure reads at 38 idle w/ pressure regulator disconnected -Replaced front 02 sensor -Replaced Fuel Pressure regulator -Replaced Cam and Crank sensors -Replaced Knock sensor -Map Sensor replaced -ECM replaced with ECM stock unit for another Impreza -Injector Resistance 15 Ohm Hot, 14 Ohm Cold -Engine pressure 170-180 PSI -Neutral safety switch reads out successfully The two standing theories (all long shots at this point) -Carbon buildup on engine heads. Fuel injector is spraying but it isn't reaching the engine due to carbon buildup. -The timing belt is a tooth ahead. I'm begging anyone with any additional theories to suggest them.

Also, something that's relevant to mention. This car is manual transmission.

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? 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.

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?

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

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?

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?

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.

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

Also, the boots were not covered in oil thankfully.

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?

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.