P0402 EGR and weird Idle - Miata Forumz - Mazda Miata Chat Forums
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Old 10-06-2011, 10:27 PM   #1  
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Default P0402 EGR and weird Idle

Ok guys, have some odd issues coming up. Not sure the exact causes here, but I have been having a high oil consumption recently. I decided to replace my PCV valve and see if that was it. Still having oil disappear, but its not as bad.

Shortly after replacing the PCV, I got a check engine code for P0402. Thats excessive EGR gas and when I get the check engine light, its accompanied by a slightly higher than normal idle (50rpm) and an even weirder symptom...When I coast in neutral, my idle is 100rpm higher than the "new" normal idle. To add some numbers:

I normally idle at about 780-810rpm.
w/ EGR CEL I idle around 850rpm.
when coasting in neutral w/ EGR CEL, my idle will bump up to 910-950rpm.

I tried rerouting the hose and that did nothing, I also hear a slight whistle sometimes, but can't tell from where. If I stick my ear to the intake manifold, I hear a good ol' whistle like a vacuum leak, but it seems to be inside...so I assume thats normal. What do you guys think? I have also cleaned the EGR valve, but not the ports on the manifold.
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Old 10-06-2011, 10:29 PM   #2  
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Also, I hooked up a vacuum gauge to the manifold in 3 places, all read at just a tad over 20 in.
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Old 10-07-2011, 08:35 AM   #3  
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tap the egr valve on its metal part with something hard (ball peen like) gently while the car is running and see if it dislodges a potentially stuck EGR valve.
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Old 10-07-2011, 08:40 AM   #4  
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will try that, I cleaned it out with some serious ---- the other day, but I will tap it and see what happens.

how can I tell if its open or closed btw? As in, if its stuck and I tap it, how will I know if something dislodged or not?
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Old 10-07-2011, 09:15 AM   #5  
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The EGR can change your idle by allowing more or less exhaust volume into the intake manifold than usual. Then the IAC will be called in to compensate but the mixture will be different from normal because exhaust doesn't equal fresh air. Also sometimes when a code is thrown it can cause the system to run in open loop instead of closed loop and that will make it run differently as well. But I'm just throwing out conjecture.

If you remove it you could use one of the cheap little manual vacuum pumps that is used for checking vacuum diaphragm movement to see if it moves freely.
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Old 10-07-2011, 09:25 AM   #6  
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hmm, this brings up another question. Can I adjust the idle at the IAC (not the bypass on top of the throttle)?

I can take it apart tonight...can I just use a two-way fluid pump to try it out? and were do I hook it up since the EGR has two ports...I take it I will need to seal one port and pump out the other?
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Old 10-07-2011, 05:28 PM   #7  
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alrighty, here is the deal. snooping around the engine bay, I hear a distinct ticking sound coming from the module at the end of the hose that goes to the boost module.

I am pretty sure thats not normal, because I shook the hose and it stopped ticking, then it start to tick again. Anyone want to tell me if that is the culprit or atleast what normal behaviour is for it? and what part # is for replacement?

also, I suspect that my egr is wide open. my MPG is suffering slightly, about 1.5-2 mpg than normal.
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Old 10-08-2011, 12:36 AM   #8  
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another weird update, my CEL turned off by itself. I still have the stored code, but the ticking stopped. is my MAP going bad? I have been trying to search for this, but I mostly end up with threads about standalones not reading MAP. I am going to take a picture tomorrow morning of the thing that was ticking near the MAP and see what you guys think. I can't seem to find a part number, but I am sure I can get one of the used sellers to get me the part.
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Old 10-10-2011, 03:51 PM   #9  
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Yeah, I'm at a loss on this one.
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Old 10-10-2011, 05:20 PM   #10  
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forgot, here is the picture:

further investigating tells me this is teh EGR VSV switch. but for some reason it connects to the fuel Evap./charcoal canister. Its not the actually EGR switch on the miata, so I think the ticking must be irrelevant?


I have just done the m.net reroute to see if that fixes it. if it does, then I will need to get on cleaning my manifold with a brush and acetone. ------- grime everywhere in that bitch I think.
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