alpop

I checked on one or two of the sensors and they had the right signal. They all have ground wires going back into the wiring harness, I assume grounded through the ECU? Not absolutely sure where the ECU is grounded, but I cleaned the likely spot near the firewall in the engine compartment. No codes are being thrown unless I mess with the sensor, wouldn't codes be thrown if ground were bad? I have shown that the ECU is not hesitant to throw a code when a sensor is disconnected.

The thing I keep coming back to is that it runs beautifully for 20 minutes when you reset the ECU, then the ECU decides to make things better and screws it all up. No CEL codes are being thrown legitimately, I only get them when I fool around with a sensor (very consistent - IAC valve, TPS, MAF sensor, etc). So it appears that the ECU does two simple things it is supposed to: 1. run on default settings for a while when its reset; 2. Throw a code for a sensor when it is disconnected. Yet when asked to do the more complex task of monitoring all the sensors and fine tuning timing, fuel/air ratio etc., it fails somewhere. Given the above, is it possible that when resets to the default settings that it could overcome something more basic like a faulty FPR? I will take a look at the FPR and make sure vacuum hose is ok, etc. The fact that (very likely) either the ECU or some sensor is screwing everything up, AND it is very capable of - but doesn't throw any codes for sensors (or anything else) on its own, makes me suspect the ECU more and more. I know - they almost never go bad, however this one may have really been stressed when the PO on purpose burned up the previous engine. After all, turns out you couldn't trust Hal -

Well I have had 3 different knock sensors on it, the original and two new ones (all read 560-580 k-ohms) so if it is a knock sensor issue it is probably the ECU responding incorrectly to each of them. I did the isolation test (removed knock sensor from engine, left plugged in, grounded it and wrapped in foam and taped to air box) with the first new knock sensor. I did conclude that things changed when I did this, and then changed again when I put it back. However this problem is so variable I can't be sure the changes in behavior were really because of my actions. Today instead of normal acceleration being restored at 3000 RPM, it was closer to 2200 several times. Don't have access to a pressure gauge, why would it do it only at lower RPMs if fuel pressure were too low?

ok so disconnected battery, reset computer and as usual it drove beautifully for 20 minutes and also CEL did not come on, then CEL came on and it still drove pretty good. But tried it this morning and same-old, same-old. I may not have mentioned that when its malfunctioning the shifts are sometimes rough also, when driving beautifully you can hardly tell its shifting. This driving perfectly for 20 minutes after disconnecting the battery should allow us to eliminate certain possibilities? Seems to me it means either 1. the ECU is receiving bad information from one of many information providers (sensors) and reacting correctly to the wrong information or 2) the ECU is receiving good information but reacting incorrectly to it. So either a sensor is bad or the ECU is bad - My tests and replacements have not identified a bad sensor. Are there other possibilities? I guess I really need to have someone in the know hook up a scan tool and drive it to see what is happening when it mal-functions.

So after driving it more with the upstream O2 sensor disconnected it malfunctioned (very poor acceleration up to 2500 rpm) on 10 of 12 attempted accelerations on a short in town trip - It is definitely doing the same thing but more of it. Any one want to hazard a guess on what this means? Anyone ever tried disconnecting the O2 sensor on a properly running Subaru and seen what happens? Guess I could try it on one of my other (non-subie) cars-

So put in another new knock sensor and it had no affect on performance. On to the O2 sensor, if outward appearance had any significance this would be it, amazingly dirty and grungy, wire and all. I now have unplugged the upstream O2 sensor and I don't think it changed much of anything - still malfunctions sometimes, maybe a little more than before, but hard to say, of course the CEL came on. Don't know what this means, question is what happens when you disconnect the O2 sensor on a properly performing car?

Hmmm, well when I reattached the knock sensor it drove perfectly for 1.5 drives but then acts up intermittently. Whereas before it always malfunctioned when engine cold, now it can be fine at first when engine's cold, but then act up later. Anyways, things do seem to change when I fool around with the knock sensor Then I looked at the manual (a little late) and saw that you are supposed to torque it to only 14 ft/lbs (this is nothing) - oops - I loosened it and torqued it right but still off and on malfunction. When I originally put the new one on I specifically remember thinking - "this thing vibrates around so I better tighten it down good" heh, I'm sure I way way over torqued it, and from what I've read this can damage the knock sensor. I ordered a new one and will torque it right this time. Worth a try for $13 anyways-

So I want to drive it a few more times for up to 30 minutes with the knock sensor isolated to see if the observed behavior of - malfunctions 'till its warmed up then drives fine after that - holds. Then I will re-attach the knock sensor and see if symptoms worsen significantly. If so then its probably a knock sensor/ecu thing, if not then it is unrelated to the knock sensor. I will then try unplugging the front O2 sensor. I also still need to take it on a longer drive/trip with the fuel injector cleaner in the gas to see if an extended drive with the cleaner in the gas will help.

Still have the knock sensor isolated, and took it out for a 30 minute drive this morning. Malfunctioned for about 10 minutes at first then after it was warmed up it drove fine the rest of the time including up hills. So it seems that with the knock sensor isolated, it malfunctions when engine is cold but is fine once its warmed up. Before isolating the knock sensor it malfunctioned most of the time cold or warm. I guess this is a clue, although I'm not sure exactly what it means. Since I replaced the old knock sensor with a new ($12) one a few weeks ago, probably not the knock sensor? Again, I never hear any spark knock. Used to have an old loyale that nobody could permanently fix the spark knock on, so I know what it sounds like. That really only leaves the ECU I guess.

Well CEL codes told me nothing; MAF which is probably due to my having disconnected it and then being unable to drive it, and knock sensor which means it doesn't like what I did with the knock sensor I guess. Drove it on an errand yesterday and it malfunctioned for the first few minutes then (I think) drove perfectly for the remaining 15-20 minutes - even did good on the hill it malfunctioned on the other day. There definitely does seem to be a change after what I did with the knock sensor, whether its causal - who knows? I also dumped in a can of Sea Foam and filled up the gas tank. Second tank of gas with a fuel injector cleaner in it. I may have to run an errand up to C'dA later this week which is 180 miles round trip. If its dirty fuel injectors maybe this will help. I have this problem where my daily driver is a bicycle, perhaps this is partly why I am moving so slow on this - I need an excuse to drive it. On a positive note I replaced the broken power antenna mast, reattached the ends of the front bumper cover so now flush with the fenders, repainted the front bumper cover (PO must not have liked the original shape/size of the car), gave it a quick wax and she is "looking" real sharp, now if I can only get it "running" right!

Thanks for the input Legacy. Your symptoms were quite different than mine, of course it might still be the O2 sensor. I am getting a little frustrated chasing a problem for which the CEL and codes are not helpful, its hard to think about changing things that cost money and are a fair amount of trouble with no indication that they are really the problem. I did isolate the knock sensor (purely as a diagnostic method) by leaving it plugged in, unbolting from engine, grounding with a wire, wrapping in foam and duct taping to the (closest) air box. Left the battery connected. Mixed results - I guess its doing it less. Whereas before it would run great for 15-20 minutes after disconnecting the battery, (but did it 95% of the time otherwise), After the knock sensor isolation I started it and it did it for about 10 minutes than it drove perfectly for another 15 minutes 'till I parked it. I drove it later in the evening for ten minutes downtown and it ran perfectly, went to a movie, came out and drove home and it malfunctioned for the middle few minutes on the way home (at the worst possible spot, climbing a steep hill). Never any engine knock when it is driving well. Just to be clear I don't need a hill for the malfunction. Its funny, when it malfunctions (accelerates very sluggishly) there is a characteristic engine/exhaust noise, not a knock but maybe like the exhaust is getting louder and sounding different? The only good thing is the CEL came on right in the middle of the hill malfunction, need to go see what that was. When it malfunctions on a hill I can solve the problem by shifting into a gear where the engine stays above 3000 RPM and leaving it there until I get to the top of the hill. Otherwise it will lose power, shift down (automatic), have plenty of power and gain too much speed so I have to let off the gas, then as a result shift back up, lose power and then shift down again, well you get the idea - ad nauseum. I about used up a tank of gas test driving it during the last month or so, so I'm going to go fill it up and dump another bottle of fuel injector cleaner into it.

So I cleaned the MAF sensor with the special cleaner, didn't look particularly dirty. No change in performance. Then I tried unplugging the MAF with the ignition off, this did not work. When started, it idled rough and when I tried to give it some gas it died, couldn't be driven. Also with MAF unplugged, check engine light came on as expected, but AT OIL light also came on flashing, after replugging in the MAF the AT OIL light stayed flashing for one or two starts then went away. Don't know if this means anything, manual says if it flashes the automatic transmission control system is malfunctioning take to dealer immediately ($$$ heh heh). Probably a result of no info from the MAF sensor? So I really don't have an answer as to whether its the MAF sensor, they are not that expensive so it might be worth just replacing ($50 or so). There was actually a recall on this year and model for the MAF sensor in 2002, when I checked with the dealer on this car they said they had records of it being replaced. Next on the list I'll try isolating the knock sensor. I read somewhere someone said when the motor mounts get old and thus the engine moves around more it can set off the knock sensor, his fix was to reattach the knock sensor to the threaded hole on the engine block (transmission?) up higher. I'm rapidly running out of possibilities-

Good information, thanks. So the ECU is doing what its supposed to do. From what you say it seems a sensor which gives input on appropriate fuel/air ratios is quite possibly the culprit. Unfortunately I think the only codes I have got are related to my fooling around with the ignition on. For example backprobing the TPS with the ignition on immediately threw a TPS code, and unplugging the IAC valve previously threw a code for it (though I thought the ignition was off, maybe there was still power to it) I will start with the MAF sensor, unplug with ignition off, good advice I was thinking of doing it with the engine running for some reason, probably something I saw on the internet.

Car drives the same with old TPS or new TPS, still hesitation problem. So I'll leave the old one in there and try to get a refund for the new one. I did the battery disconnect test again (3rd time) and once again it drove great for 15-20 minutes but then started acting up. So the I think the ECU is definitely complicit, even if it may not be the origin of the problem. I am now focusing on the MAF sensor and the knock sensor again. The airbox closest to the throttle body actually had a few tablespoons of oil in it when I got the car, even though no oil in throttle body. I cleaned it out and it has not reappeared. I figure when the previous engine was burned up, oil must have come thru the old throttle body into the airbox. I guess its possible it continued to some extent all the way to the MAF sensor and gunked it up. I've read that you can just disconnect the MAF sensor and if the problem goes away then there's your problem? I also plan to take a look and clean the wires on the MAF sensor with the special spray cleaner.

So I did put the old TPS back in and tested it with the good multimeter, it looks fine, no dead spots.

Yes, the two airboxes are weird, had something to do with CA emissions.When I first got it I thought it didn't have an air filter, then I discovered the second box with the filter. The first box has just the rubber perimeter piece that seals the box but not the paper element part of it. I did an extensive search/test for air intake leaks including a fine mist of water all around any possible intake leak sites (don't like the idea of spraying a flammable liquid around a running engine), found nothing. There is a tiny spot of bare wire right where it goes into the MAF plug, insulation must have rubbed away. I sort of put a little electrical tape around it, but because of the location it was very hard to secure well. Have't had any MAF codes.

I did not re-install the old TPS and voltage test it with the "good" multimeter, maybe I should. Yeah, for $140 maybe I should consider sending the new one back. Knock sensor was 2nd or 3rd replacement item. However maybe I should try the isolation test with it? Physically remove from engine, isolate in padding, leaving it plugged in. How about those crankshaft and camshaft sensors? What sensor inputs to the tachometer (crankshaft position?) If so its not that since it seems to be reading the RPMS rightI I guess a mal-functioning camshaft position sensor would throw off the timing and give the observed symptoms maaybe? I keep coming back to the ECU, one strange thing I have noticed is if I disconnect the battery for a little while then re-connect it, it drives beautifully for about 20-25 minutes before starting to act out again. I will try this a 3rd time and see. As mentioned earlier I read an account of someone having this exact problem with a 1999 with an automatic, solving it by installing an "older" ECU in the vehicle. There was a TSB for 1998 manual shift 2,2L for ECU responding to the knock sensor incorrectly. Subaru wouldn't send the TSB to me since my VIN# indicated a 1999 and automatic. Yeah, I'll try the disconnect battery test first, and then the knock sensor isolation test. If both tests correct the problem (temporarily and more permanently) it might be ECU response to knock sensor.

So I still have the intermittent acceleration problem even with the new TPS - foiled by a defective multi-meter (its in the garbage). Should have admitted this before, can't be an issue with the throttle position. I can start from a stop and keep the pedal/throttle in the same place - maybe halfway down, and it lags and lags and lags at lower rpms then finally hits 2500-3000 rpm and it takes off, then shifts gears and lags at the lower rpm again then takes off at higher again, etc. All the time not changing the pedal/throttle position. If you are impatient you can floor it at which point it shifts way down and takes off (at high RPMs obviously) So its really a lower engine RPM issue. I feel like I'm on a wild goose chase - and losing. What measures engine RPM? It looks to me like perhaps faulty crankshaft position sensor or camshaft position sensor could give these symptoms. No codes for these, guess I should check the wiring/plugs on these next.

Tried another multimeter, no micro dead spot, although this one shows an instantaneous jump to 5 volts right at 4 volts - weirdness, nothing is as it seems. No, I'm not going to put the old TPS back in and test it with the 2nd multimeter and see if there is still a (much bigger) dead spot. I'll leave the new TPS in there and see how it drives. Ha, but I drained the battery with something I was doing, guess I left things hooked up for three days. Oh well, wait 'till the morning to jump it.

Got the new $154 (it said Standard on the internet but the box says Intermotor/SMP) TPS, anyways its weird. The old one had a gap or dead spot from about 3.0-3.4 volts, sometimes 2.8 - 3.4, this one has a tiny (very repeatable) dead spot from 3.21 - 3.27 volts going up and about 2.82-2.75 going down? Could the new one be defective? Guess I should throw things back together and see how it drives.

Assuming that this indeed is the problem, I spent so much time figuring it out that I just want to make sure I'm done with it - so I ordered the new one from Amazon with free three day shipping (best price and best shipping). Hoping to use the car for a trip later this week. I would hate to get a used one, test it, and find a dead spot on it also! BTW the engine is supposed to have around 140k on it, the TPS in there sure looks original (grungy) and there is a paint slash across the unit and screw indicating where it is adjusted to. This is the case with many of the engine fittings that are adjustable (paint slashes) and I assume it came from the factory that way? Thanks for all that info on the ECU and IAC valve - explains a few things and good to know.

One of the first things I did when I got the car was clean-up the throttle body, it wasn't very dirty. I have replicated the dead spot at least a dozen times going both up and down, sometimes it extends to 2.5-3.5 volts, always does it some with that weird buzzing (TPS I think). I could probably adjust the TPS and bring the starting voltage down, but this wouldn't fix the dead spot which is probably most of my problem. One (very) funny thing is sometimes I don't need to have the ignition on to get the voltage out of the TPS, I checked and none of the other ignition on things (radio, cabin fan etc.) work in this situation with the key out of the ignition. The TPS in there is identical to an Airtex with the writing A22-667-ROO on it, adjustable and 4-pins, $179 at Rock Auto. Saw a used one on e-bay for $50ish, but not sure I want to fool around with this again.

Actually that Beck Arnley looks like a three pin and my TPS is a 4-pin, It looks like my automatic takes the 4-pin TPS. Funny, my TPS has 4-pins but the connector only uses three of the spots with only 3 wires coming out of it? Anyways looks like I need the Standard Motor Products TH389 running more like $154.00

Alright I think I have a diagnosis. I finally got a chance to backprobe the TPS (really not that difficult), Su bah roo'n said it should start at 0.45-0.55 throttle closed, then as depress pedal should gradually increase evenly to 4.5-5.5 (?) WOT. Here is what I see: starts at 0.58 - throttle closed increases gradually to about 3.0 then goes blank - no signal continue depressing further and it picks up at about 3.4 and continues to 4.2 tops at WOT so looks like it starts high and ends low with a pretty big dead spot from 3.0=3.4 v. (sounds like my workout) Also there is an engine buzzing noise with ignition on as I do this, is this normal? Amazon has the exact TPS that is in there (I assume its OE), Beck Arnley 158-0555 for $116.00, best price that I have found. Yes?

So I put new wires on this morning (Import Direct supposedly re-boxed OE), the resistance on the old ones was 10-12k and new ones were 6-7K, so the ones on there were definitely not new. I disconnected the battery again while doing it. Drove for about 20 minutes to a nearby town and it ran/drove beautifully, stopped and turned around and it started bogging down again until 2500 rpm. Only thing is I swear its not as bad as it was. Once again it didn't start doing it until 5-10 minutes after the car was fully warmed up - after I had previously disconnected the battery. Left it all day (battery connected) and when I drove it home it started doing it immediately (cold engine), but once again it didn't seem as bad. Could it be something with the ignition, and the new wires alleviated the problem a little? Or is the fuel injector cleaner I dumped in with this tank of gas starting to work a little? Is the ecu screwing something up and when I reset things (battery disconnect) it takes longer to screw things up again? Still need to run that TPS test-