Hanging rpms and lean codes... - Mustang Evolution

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Old 07-27-2016, 12:35 AM   #1
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Hanging rpms and lean codes...

So I've got a 2003 3.8 v6 5speed, just did plugs, wires, coil pack, IAC, cleaned the MAF, throttle body, and changed the fuel filter. Ran great for about 50miles, then the rpms started to hang when shifting and when coming to a stop. Doesn't matter where I shift from, 1500 rpms 2000 rpms etc. I found that I can do a IAC mod and make the wholesale smaller so I'm going to do that, for nown the iac is just unplugged to get rid of that issue. The other issue I'm having problems with is it also produced codes p0171 and p0174 (bank 1 and 2 too lean) along with these issues. I've read all over forms, most say check your vacuum for leaks. I've done that, and the only thing I removed during the install of the parts was the air intake which is a basic k&n. It's all tight. What could possibly make the sudden CEL after the tune up? I don't have issues idling, just hanging rpms.

Mods - CAI, 93 sct tuner, v8 exhaust port.
The plugs I just put in are Plat ngk, 8.5mm mds wires, mds coil pack
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Old 07-27-2016, 08:48 AM   #2
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It certainly sounds like you have a fair sized vacuum leak. Get some carburetor cleaner and, with the engine running, spray it everywhere that could possibly cause a vacuum leak. If there is a leak, the carburetor cleaner will change the idle of the car, and you will have found the source of the leak. And re-inspect the intake tube installation. I have a KN CAI on a Chevy truck and it is constantly becoming loose, and falling off.
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Old 07-27-2016, 11:46 AM   #3
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Alright so I sprayed carb cleaner, found that spraying the top of the throttle body itself where the gasket is caused a slight raise in rpms, maybe 100-200rpms. I'll replace the gasket after work tonight but would that be enough to send those codes and cause a hanging rpm when shifting?
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Old 07-27-2016, 12:11 PM   #4
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It is entirely possible that is the problem. It is an excellent place to start, in any case.
Before you replace the gasket, disconnect the negative side of the battery and leave it disconnected for 20 minutes or so. That will clear the codes, and the idle memory, and will allow the computer to relearn the new idle trim.
Hopefully, that will solve both the lean codes and the hanging idle.
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Old 07-27-2016, 12:28 PM   #5
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Quote:
Originally Posted by straybullitt View Post
It is entirely possible that is the problem. It is an excellent place to start, in any case.
Before you replace the gasket, disconnect the negative side of the battery and leave it disconnected for 20 minutes or so. That will clear the codes, and the idle memory, and will allow the computer to relearn the new idle trim.
Hopefully, that will solve both the lean codes and the hanging idle.
I've done the idle reset a few times, every time I tweak something really. Hasn't fixed anything.
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Old 07-27-2016, 12:33 PM   #6
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Do it anyway.
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Old 07-27-2016, 02:39 PM   #7
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Found the pcv valve basically just sitting in the grommet. Wasn't tight at all I'm guessing I bumped it last night doing the plugs and wires. Now idle reset after work and hopefully it clears the p0174 and p0171 codes.
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Old 07-27-2016, 05:26 PM   #8
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When a problem occurs immediately after working on the engine, it is usually something simple that was overlooked.

Let us know how it works out.
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