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I picked up this little truck, a 1998 Frontier with the 2.4l engine, with 250k on the odometer. It's been very handy for trips to Lowes/Home Depot and to the dump to haul trash during the purchase of a new home. It runs great when I'm driving, but I have been chasing a bad idle and bad MPG since I bought it... Sorry for the wind noise, these clutch radiator fans just blow so good! https://twitter.com/dfwlly/status/1462863986509107200?s=20 Replaced so far: Injectors Fuel pressure regulator EGR and EGR vacuum solenoid Idle air control valve, and fast idle control valve MAF Throttle body gaskets, throttle body spacer gasket and last but not least, the PCV valve (wow what a pain to get to) So like I mentioned, it has no misses when I am on the throttle. Revs great, drives great on the interstate too. It idles like this constantly, no matter the operating temperature, and the MPG I am getting is horrendous. There is a smell of unburnt fuel I feel like which is why I thought the injectors needed replaced due to them leaking, but they weren't after all. I have checked numerous times for vacuum leaks and cannot find any. I have tried soapy water on various tubes, smoke on various tubes, and spraying brake clean on various tube fittings. The idle is always this way. Initially I had an EGR code which was why I replaced the ERG vacuum solenoid and EGR valve (also a nightmare to get out with this many miles). My last step will be to replace the O2 sensor up top on the exhaust manifold, but I am doubtful that will do anything for the idle. Any thoughts?
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Nov 23, 2021 14:04
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| # ? May 3, 2024 07:22 |
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It sure sounds like a vacuum leak. Have you carefully inspected any intake tubing downstream of the air flow sensor? My brother's old Altima with a KA24DE had repeated troubles with the optical sensor inside the distributor. I don't think it ever led to the symptoms you're describing though. No check engine light or codes? PBCrunch fucked around with this message at 23:15 on Nov 23, 2021 |
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Nov 23, 2021 23:11
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So the FWD KA used in the Altima uses a different distributor setup vs the RWD version. The FWD one is cam driven and bolts to the head, and that's the one that's prone to oil fouling the optical sensor in it. The RWD version bolts to the timing cover, and sticks up instead of sideways - it's much less likely to get oil inside it. The FWD distributor also doesn't have much in the way of adjustability for timing, while the RWD version has a bit more adjustment available - so the timing could be a bit off. OP, the KA isn't a refined engine, but it should idle smooth and get fairly decent MPG. You're right in that the O2 sensor won't affect idle much, if at all; the way it's idling sounds like it's trying to compensate for a bad vacuum leak (one bad enough that it's struggling to keep idling). Out of curiosity, is the oil dipstick firmly in place, and sealing? I remember my old Altima (same engine) would idle like poo poo if it wasn't in all the way. Same if the oil filler cap was loose. A vacuum leak will also throw off the fuel trims, enough for it to smell gassy. It takes a lot for them to throw a fuel trim code, at least on a 99 Altima. Also, try removing the vacuum line from your brake booster, and putting your finger over the line. If it smooths out, your brake booster may have a vacuum leak (it would also explain why you're not hearing a hissing under the hood). Finally, the knock sensor is famous for going bad on these and causing it to pull timing hard (you wind up with very little power and horrible MPG). The service manual has you remove the intake manifold to get to it; you can get to it from below though. It's near the PCV valve. Just unplug it, it'll run fine without it and won't turn on the check engine light (it likely already has the knock sensor code stored anyway). It sits between the #3 and #4 intake runners if I remember right; you have to unplug it by feel.
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Nov 24, 2021 05:19
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Correct on no CEL and no codes. I have driven it probably 50 miles since I posted this thread and no codes on the tester and no CEL. The only code I had was initially when I bought it, for the EGR solenoid, which went away after replaced. I will check both of your guys suggestions and continue to look for any vacuum leaks as well. I know a bad knock sensor would throw a CEL, but I am going to disconnect that and see what happens while it's running. It doesn't seem down on power but they are down on power from the factory though lol. Thanks for the suggestions, will report back.
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Nov 29, 2021 13:59
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The knock sensor will NOT throw a CEL on its own - it'll store a code, but that's it. And even then they don't always store a code when they go bad on that engine.
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Nov 30, 2021 01:39
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Well, I disconnected the knock sensor. No change. I checked for leaks at the break booster, none there , vacuum is strong on that hose too. Checked for leaks around the intake manifold and throttle body and couldn't find any. I am going to replace all of the vacuum lines to the throttle body.
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Dec 8, 2021 17:20
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I'd suggest that you go buy a cigar or a vape rig and puff those dragon clouds into the vacuum hoses before you just start blindly firing the parts cannon.
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Dec 8, 2021 21:48
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PBCrunch posted:I'd suggest that you go buy a cigar or a vape rig and puff those dragon clouds into the vacuum hoses before you just start blindly firing the parts cannon. Another cheap way is to (on a not super-hot engine) spray flammable carb or brake cleaner around. If the idle changes you know you've found a spot.
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Dec 9, 2021 04:10
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PBCrunch posted:I'd suggest that you go buy a cigar or a vape rig and puff those dragon clouds into the vacuum hoses before you just start blindly firing the parts cannon. Too late... Replaced so far: Injectors Fuel pressure regulator EGR and EGR vacuum solenoid Idle air control valve, and fast idle control valve MAF Throttle body gaskets, throttle body spacer gasket and last but not least, the PCV valve rifles posted:Another cheap way is to (on a not super-hot engine) spray flammable carb or brake cleaner around. If the idle changes you know you've found a spot. Have done this as well  My driveway is a puddle of brake clean.
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Dec 13, 2021 03:23
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| # ? May 3, 2024 07:22 |
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Have you put a vacuum gauge on it and what do the plugs look like?
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Dec 16, 2021 02:26
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