mechanic58 Posted May 30, 2019 Posted May 30, 2019 Everytime I get a CEL for something stupid on this car and I hook my scanner up to read and clear the code it appears that all the stored "learned" data in the PCM is erased and it takes several days of driving before it will start acting right again. One of the most annoying symptoms is super-low idle speed. Like less than 500 rpm - so low that the power steering pump load will stall the engine when you're trying to maneuver in a parking lot, etc. Why does this happen and is there anything I can do to thwart this? There doesn't appear to be any fittings on the throttle body that would allow you to make an idle speed adjustment.
mechanic58 Posted May 30, 2019 Author Posted May 30, 2019 Forgot to mention this is an '09 Legacy 2.5i. Same thing happens if the battery is disconnected. I am wondering if there's a battery on the circuit board in the PCM that has gone dead that causes the memory loss everytime the power is interrupted.
08SpecB_DE Posted May 30, 2019 Posted May 30, 2019 Either/or causes the car to go back into learn mode. I leave the key on, engine off for about 10 seconds after clearing codes (after going back to off position) or disconnecting the battery. Then, start and idle the car for over 10 minutes (longer the better). After that, go put some miles on it (10-15). That should get it back to normal or close to it.
mechanic58 Posted May 30, 2019 Author Posted May 30, 2019 I have tried that, no dice. I forgot to mention also - after I clear codes it cranks for an unusually long time before it will start...like 8-10 seconds.
DaveWaters Posted May 31, 2019 Posted May 31, 2019 I have tried that, no dice. I forgot to mention also - after I clear codes it cranks for an unusually long time before it will start...like 8-10 seconds. Are you letting the gauge sweep complete before cranking?
mechanic58 Posted May 31, 2019 Author Posted May 31, 2019 Might have a fuel pump on the verge of failing. Only does it on the first start attempt after a code wipe. Runs fun otherwise. Are you letting the gauge sweep complete before cranking? Yes.
08SpecB_DE Posted May 31, 2019 Posted May 31, 2019 Have you tried leaving the key on for 10 seconds? It's normal for this to happen but I've noticed starting before the throttle plate has a chance to calibrate will cause an extended crank.
mechanic58 Posted May 31, 2019 Author Posted May 31, 2019 Have you tried leaving the key on for 10 seconds? It's normal for this to happen but I've noticed starting before the throttle plate has a chance to calibrate will cause an extended crank. No matter what I do, the first start after a code wipe always takes an extended amount of time. Even if I wipe it and let it sit overnight before trying to start it again. This only happens on the first start, all subsequent starts are normal. It just idles too low for several dozen drive cycles after a wipe. Usually takes a couple weeks of normal driving for it to finally start acting right. Its ridiculous. Then bout the time it starts acting right it’ll pop another bs code and I have to start over again because if I don’t clear it out the ****ing cruise control is disabled. I truly hate this car. If I could get my hands on the mfr that designed the pcm logic I would choke him to death. Totally ruined a potentially great car.
bergs Posted May 31, 2019 Posted May 31, 2019 Seems to me that fixing the source of the CEL will solve a lot of your issues (and hatred) for your car.
mechanic58 Posted May 31, 2019 Author Posted May 31, 2019 Seems to me that fixing the source of the CEL will solve a lot of your issues (and hatred) for your car. I do fix these problems, but every time I fix one a few weeks later a new one pops up. Lately the recurring issue has been with the VVL circuit. As these engines get a lot of miles on them all of that hardware gets a little bit looser. It creates a delay in the oil pressure feedback to the VVL pressure switch. Most of the time it works OK but under certain conditions There’s enough of a time delay to cause the PCM to set a P0028 code. There’s not much I can do about it aside from putting a brand new engine in the car. I’m about to wire in an 86 relay in place of the pressure switch and signal it off of the signal wire on the solenoid. This will eliminate the time delay. Or I might just get rid of the car.
ehsnils Posted May 31, 2019 Posted May 31, 2019 Since this is an electrical gremlin - check all your grounding points and make sure they are good and clean. Especially between engine and chassis. Also battery connectors and the main power in the fuse box including the main fuse.
AWDFTW Posted May 31, 2019 Posted May 31, 2019 I think you need a different vehicle. I can't recall you posting anything positive about this one.
mechanic58 Posted May 31, 2019 Author Posted May 31, 2019 Since this is an electrical gremlin - check all your grounding points and make sure they are good and clean. Especially between engine and chassis. Also battery connectors and the main power in the fuse box including the main fuse. I had the engine out of this car several months ago. I checked all that stuff then. In fact I replaced all the ground straps, they were in bad shape. The car sat idle for about 18 months because the engine was blow’d up. I think you need a different vehicle. I can't recall you posting anything positive about this one. I think you are correct.
lilredwagon Posted May 31, 2019 Posted May 31, 2019 After an ECU reset, I usually let it sit with the key on until you hear a click from the glovebox area. That click let's it start. My guess is that the ECU does some quick checks the first time after a reset. It should only take a couple seconds longer than the gauge sweep. So turn it on, watch the gauges sweep, wait for maybe 3-5 seconds, hear the click, then crank. If you don't do that, it'll just be cranking for those first few seconds. In either case, it should start like normal after that click. It hunts for the idle speed for the first couple starts after a reset. It's just setting the fuel trims for whatever variables it sees. One of those variables is intake air temps. These temps change drastically throughout the day and under different conditions. For example, sitting in traffic, I'll see intake temps rise up to the 120* range, on a cold start at night I'll see intake temps in the 50-60* range. If I start the car a few times during the day, like if I'm running errands, I'll see intake temps all over the map if it heat soaks while parked for a few minutes. Each time the ECU sees an intake temp or condition for the first time, it will hunt for idle and set fuel trims that correspond to that set of conditions. The next time it sees that condition, it goes to the logged fuel trim, and idle should be smooth. It's frustrating and annoying, I know. I have been chasing a CEL that occasionally comes on after all my readiness monitors come online. One thing that really helps is to keep the MAF super clean. Even if you've cleaned it recently, clean it again. If you cleaned it just last week, clean it again. I don't know why it needs to be that spotless, but it seems to help.
mechanic58 Posted May 31, 2019 Author Posted May 31, 2019 After an ECU reset, I usually let it sit with the key on until you hear a click from the glovebox area. That click let's it start. My guess is that the ECU does some quick checks the first time after a reset. It should only take a couple seconds longer than the gauge sweep. So turn it on, watch the gauges sweep, wait for maybe 3-5 seconds, hear the click, then crank. If you don't do that, it'll just be cranking for those first few seconds. In either case, it should start like normal after that click. It hunts for the idle speed for the first couple starts after a reset. It's just setting the fuel trims for whatever variables it sees. One of those variables is intake air temps. These temps change drastically throughout the day and under different conditions. For example, sitting in traffic, I'll see intake temps rise up to the 120* range, on a cold start at night I'll see intake temps in the 50-60* range. If I start the car a few times during the day, like if I'm running errands, I'll see intake temps all over the map if it heat soaks while parked for a few minutes. Each time the ECU sees an intake temp or condition for the first time, it will hunt for idle and set fuel trims that correspond to that set of conditions. The next time it sees that condition, it goes to the logged fuel trim, and idle should be smooth. It's frustrating and annoying, I know. I have been chasing a CEL that occasionally comes on after all my readiness monitors come online. One thing that really helps is to keep the MAF super clean. Even if you've cleaned it recently, clean it again. If you cleaned it just last week, clean it again. I don't know why it needs to be that spotless, but it seems to help. Thanks for that info. The long start isnt so much the concern, like I said it only happens once. If the engine is cold it will fast idle in open loop for a few mins like its supposed to, but once it settles out it idles entirely too low. It takes several start/run/drive cycles for it to straighten out. I’m bout to drill a small hole in the throttle plate.
lilredwagon Posted May 31, 2019 Posted May 31, 2019 Are you tuned? If it only happens on cold starts, it might be your warmup tables. But if you're totally stock, then it should work with the stock tune (obviously).
mechanic58 Posted June 1, 2019 Author Posted June 1, 2019 Are you tuned? If it only happens on cold starts' date=' it might be your warmup tables. But if you're totally stock, then it should work with the stock tune (obviously).[/quote'] Nope, bone stock.
08SpecB_DE Posted June 1, 2019 Posted June 1, 2019 Go back to my first post. I've done it several times on my own vehicle and many more on other cars. They are all relearned that same day. Can't send a customer on their way stating it's going to idle low and possibly stall out every time they come to a stop. I assure you I'm not driving their cars around for days, more like ~30 minutes from beginning to end (depending on traffic).
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