twojtyniak Posted October 30, 2009 Share Posted October 30, 2009 The Facts: 2002 Legacy Outback wagon 2.5 l 5-speed New, correct NGK plugs New wires New coil pack The Problem: Intermittently (of course) when driving, either accelerating or constant speed, the car will stumble and lose power as if the power was pulled back to idle. It does not stall. Sometimes it recovers on its own, other times I clutch it and rev it and it recovers. Sometimes it backfires if the throttle is held steady. Sometimes it doesn't recover, but if the revs are high enough (2200+?) I can floor it and the engine will run well enough to maintain speed or keep accelerating, but it does not run correctly. The behavior stops and starts instantly, like a switch being thrown. The check engine light was not on for quite a long time while the behavior was occurring, but is on now. Earlier when exhibiting this behavior the codes had been misfire and running rich, but I haven't had the code pulled again yet. The Hunch: Some sensor is misbehaving, but not going out of range, so the computer can't identify the cause. On a Ford EEC-IV at full throttle the car would be in open loop, running strictly off of default values from a table rather than sensor input. At part throttle it is in closed loop mode, dependent upon sensors. I just don't know which sensor might cause this behavior. Things that do not appear to be factors: Outside temp, engine temp, engine speed, vehicle speed. The coil was swapped but did not change the behavior. The new wires did not change the behavior. The plugs were changed quite some time before the behavior started. Any ideas? TIA, Tim Quote Link to comment Share on other sites More sharing options...
CNY_Dave Posted October 30, 2009 Share Posted October 30, 2009 I have seen descriptions on this site that sound like this- sometimes it's the cam position sensor, and is there also a sensor on the crank? Or is the one on the crank the CPS? Dave Quote Link to comment Share on other sites More sharing options...
Olnick Posted October 30, 2009 Share Posted October 30, 2009 Pull the codes again and post them here (the code numbers, not a verbal description.) Quote Link to comment Share on other sites More sharing options...
OB99W Posted October 30, 2009 Share Posted October 30, 2009 Welcome to the forum. I agree that the problem could be caused by something not being sensed correctly, and that the ECU then defaults to some fail-safe (''limping'') mode. Unfortunately, there are several possible causes. Having the code(s) in the form Pxxxx (where the x's are numbers) would be helpful. Having said that, one thing that can be intermittent and cause erratic fuel delivery is if the ECU doesn't know whether the car is in gear or not. The neutral switch could be intermittent. If one of the codes is P1507, see http://endwrench.com/images/pdfs/DiagTroubSum04.pdf . Otherwise, let us know what turns up. Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted October 30, 2009 Share Posted October 30, 2009 This sounds like a fun one. It only does this when driving, correct? There are quite a few things that come to mind, but knowing which DTCs it is throwing will help steer diagnosis in the right direction. Quote Link to comment Share on other sites More sharing options...
twojtyniak Posted October 30, 2009 Author Share Posted October 30, 2009 Thank you for the preliminary thoughts and the guidance in providing further data. I will get the codes ASAP, but note that for a few days of driving the CEL was not on although the car was exhibiting the behavior. It's a puzzlement. Quote Link to comment Share on other sites More sharing options...
nipper Posted October 30, 2009 Share Posted October 30, 2009 First thing that came to mind Engine knock sensor. nipper Quote Link to comment Share on other sites More sharing options...
valvestem Posted October 30, 2009 Share Posted October 30, 2009 Battery/alternator low voltage/output, or battery cable internal corrosion, causing loss of voltage to coil/ignition? Easy to check. Quote Link to comment Share on other sites More sharing options...
Log1call Posted October 31, 2009 Share Posted October 31, 2009 Dirty fuel filter? Bad connector(under the back seat) to the fuel pump. Faulty fuel pump relay? Quote Link to comment Share on other sites More sharing options...
ronemus Posted October 31, 2009 Share Posted October 31, 2009 I'd bet on the MAF/MAP sensor or throttle position sensor. I had exactly the same problem when the MAF sensor on my Celica GT would drop out, so it only fueled for idle conditions; it idled perfectly, but wouldn't rev over 2500 rpm. It felt exactly like somebody threw out an anchor, but if allowed to cool off it would work perfectly until the next time. It was only diagnosed when I was able to limp to a dealer during business hours and have them diagnose it while it was actually malfunctioning. Quote Link to comment Share on other sites More sharing options...
msmithmmx Posted October 31, 2009 Share Posted October 31, 2009 I was going to say coil but you replaced that. I am thinking cam or crank sensor. Do you have a yard near you? get those things for 5 bucks a pop. Quote Link to comment Share on other sites More sharing options...
nipper Posted October 31, 2009 Share Posted October 31, 2009 Do we have any codes yet? nipper Quote Link to comment Share on other sites More sharing options...
forester2002s Posted October 31, 2009 Share Posted October 31, 2009 Dirty fuel filter? Ditto Quote Link to comment Share on other sites More sharing options...
EVOthis Posted October 31, 2009 Share Posted October 31, 2009 I was thinking front o2/AF sensor... Quote Link to comment Share on other sites More sharing options...
twojtyniak Posted October 31, 2009 Author Share Posted October 31, 2009 Thank you for the ideas. Other than remove and replace does anyone have ideas how to test/rule out any of these particular problems? The mechanics checked the TPS according to procedure and ruled that out. It sounds like the problem ronemus had matches pretty well, as the car will idle just fine. Any ideas how to test the MAF? And the codes are (drum roll, please): PO301 PO302 PO303 PO304 PO172 I'll replace the fuel filter just to be sure, but it sure seems electrical in the way it turns off and on at will. Shaking the car around doesn't seem to affect the problem. It did seem to run better for quite a while after being on a bumpy road, but it also has had long periods of running well after a bad spell without any bumps involved. Quote Link to comment Share on other sites More sharing options...
nipper Posted October 31, 2009 Share Posted October 31, 2009 Clear the codes. Soak the coils with a bootle of spray water while the car is running and look for sparks. Clean the terminals for the coils and the ignitor. Check the engine grounds. What brand sparkplug wires were used? What brand plugs? nipper Quote Link to comment Share on other sites More sharing options...
OB99W Posted October 31, 2009 Share Posted October 31, 2009 [...] It sounds like the problem ronemus had matches pretty well, as the car will idle just fine.[...]PO172 Besides MAF/MAP, check connections at the intake air temp sensor and especially those at the engine coolant temp sensor (they sometimes seep coolant and corrode the contacts). Quote Link to comment Share on other sites More sharing options...
church272003 Posted October 31, 2009 Share Posted October 31, 2009 MAF sensor, I had a similar problem on my Taurus SHO, it had me stumped for a while, but they are alot of money, I would do more tests before buying one. Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted October 31, 2009 Share Posted October 31, 2009 (edited) P0301-4 Misfire in cylinder 1 - 4. The last number is respective to the cylinder which has experienced the misfire. P0172 is probably caused by the misfiring, but could also be an O2 sensor on the way out. The O2 sensor can also cause misfiring, though the intermittance may point to a bad connection. I second Nippers suggestion to spray down the ignition coil and spark plug wires and look for arcing. edit: adding on. You could also try unplugging the wire harness connectors for the ignition coil and make sure it is free of dirt, water, and corrosion. The MAF sensor can be cleaned with a special cleaner available at most auto parts stores. Its usually about $4 or $5 a can and is easy to use. It only does it when driving, so it could be something to do with the knock sensor. That is easy enough to remove and inspect. Generally if the case has any cracks, it is possible that moisture has gotten inside and corroded the sensor. Edited October 31, 2009 by Fairtax4me Quote Link to comment Share on other sites More sharing options...
lostinthe202 Posted November 1, 2009 Share Posted November 1, 2009 (edited) OP states in the first post that plugs (NGK), wires and coil(s?) are all new. Could still be arcing I suppose, but... As for testing the MAF, I've read many posts about testing MAF sensors by tapping them with the butt of a screwdriver while the car is idling. If the idle stumbles, the MAF is bad. I realize this is far from a comprehensive test, but it is easy to do. Edited November 1, 2009 by lostinthe202 wrong but, butt Quote Link to comment Share on other sites More sharing options...
OB99W Posted November 1, 2009 Share Posted November 1, 2009 (edited) I had mentioned the neutral switch earlier. A new post (#56) in http://www.ultimatesubaru.org/forum/showthread.php?t=85794&page=6 might be worth reading. EDIT: Just to verify my suspicions, I did a bit of searching and came across http://bbs.scoobynet.com/general-technical-10/491306-misfire.html . The OP's problem might not be the switch, but investigating it is probably justified. Edited November 1, 2009 by OB99W Quote Link to comment Share on other sites More sharing options...
nipper Posted November 1, 2009 Share Posted November 1, 2009 OP states in the first post that plugs (NGK), wires and coil(s?) are all new. Could still be arcing I suppose, but... As for testing the MAF, I've read many posts about testing MAF sensors by tapping them with the butt of a screwdriver while the car is idling. If the idle stumbles, the MAF is bad. I realize this is far from a comprehensive test, but it is easy to do. We like easy Quote Link to comment Share on other sites More sharing options...
ferret Posted November 1, 2009 Share Posted November 1, 2009 I was thinking front o2/AF sensor... Yup, I agree here ... misfires and fuel trim lean .... front O2 sensor. No MAF on his, he has a MAP. 00-02 Subarus are known for this behavior. Easy way to check, when it's acting up, unplug the front O2 sensor. This WILL set a code, but the ECU will run in open loop mode. And if the hesitation goes away, you confirmed your culprit. Usually happens AFTER it warms up, and the engine goes into Closed-Loop mode. Quote Link to comment Share on other sites More sharing options...
twojtyniak Posted November 1, 2009 Author Share Posted November 1, 2009 Thank you again for the ideas. I'll do some investigating today and let you know what I find. Quote Link to comment Share on other sites More sharing options...
EVOthis Posted November 1, 2009 Share Posted November 1, 2009 Yup, I agree here ... misfires and fuel trim lean .... front O2 sensor. No MAF on his, he has a MAP. 00-02 Subarus are known for this behavior. Easy way to check, when it's acting up, unplug the front O2 sensor. This WILL set a code, but the ECU will run in open loop mode. And if the hesitation goes away, you confirmed your culprit. Usually happens AFTER it warms up, and the engine goes into Closed-Loop mode. +1..There was also a TSB for the o2/AF sensor this year.... Quote Link to comment Share on other sites More sharing options...
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