rough idle, code p0304

2009 TOYOTA COROLLA
185,000 MILES • 1.8L • 4 CYL • 2WD • AUTOMATIC
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STEVEDI
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Hi,

The car is idling poorly when in drive with brake applied. It levels out in park or neutral. It intermittently throws a P0304 code. I have:
1. cleaned throttle body.
2. cleaned MAF sensor.
3. changed plugs.
4. switched the number one coil with four and the code returns on four.
5. singularly disconnected each coil and injector. Appropriate changes were noticed for in each.

I have not done a compression test (almost afraid to know the answer). Wondering if an intake manifold gasket leak or other vacuum leak could effect just that one cylinder.

Thanks.
Apr 11, 2018 at 10:36 AM
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MHPAUTOS
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do the compression test, and check for the vacuum leak around number four cylinder. you can get a broken gasket that will only affect one cylinder, this is a fairly common problem.
Apr 11, 2018 at 10:50 AM
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STEVEDI
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Excellent! Will do. Thanks
Apr 11, 2018 at 11:04 AM
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MHPAUTOS
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let me know how you get on, good luck.
Apr 11, 2018 at 11:07 AM
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STEVEDI
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Addition question. Could a bad intake manifold gasket cause a ticking sound?
Apr 12, 2018 at 7:55 AM
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MHPAUTOS
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No an inlet will be a vacuum hiss noise, ticking will be exhaust or a mechanical problem, like valve clearance issue.
Apr 12, 2018 at 7:58 AM
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STEVEDI
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Hi, I took your advice and did the compression test. Here are the numbers:
#1: 85 psi
#2: 90 psi
#3: 160 psi
#4: 170 psi
Yikes!!
Thanks for your help.
Apr 14, 2018 at 2:54 PM
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MHPAUTOS
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Looks as if you have found the problem, looks as if you may have a breach between the two cylinders, a leak down test will prove this.
Apr 14, 2018 at 5:05 PM
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