Rough idle and smooth idle

Tiny
MARKAU
  • MEMBER
  • 1999 HONDA CIVIC
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 106,000 MILES
My 99 Civic EX (all stock) with 106K miles and a D16Y8 engine, started rough idling 95% of the time (vibration felt through the steering wheel below 1000 RPM). It runs smooth above 1000 RPM and fuel economy is great. Occasionally the idle drops down to 500 to 600. No codes in the computer. I changed plugs/plug wires, dist. Cap/rotor, air filter, set valve clearances (all were within spec already but reset them anyway), checked and set timing using an SCS connector and service manual (found it 10 degrees too far advanced, reset to 12 degrees before TDC), checked timing belt placement in relation to camshaft pulley and crank pulley, removed/disassembled/cleaned the throttle body, IAC valve, and idle adjust screw (all were dirty), and checked idle speed. I add Chevron Techron to my fuel twice a year. As a last resort I also used Gunk motor flush at last oil change. During cold weather warmup, the engine clacks or chatters. As the outside air temp has been above 65 lately, I notice smoother idling 25% more often than in winter. As a final note, as the fuel tank gets closer to empty, it takes a few more seconds of cranking before the engine will start, and it never did this the first 7 years of ownership.
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Thursday, May 1st, 2008 AT 5:40 PM

45 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check the fuel pressure fuel pump could be getting sloppy and on its way out-
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Thursday, May 1st, 2008 AT 5:58 PM
Tiny
LEGITIMATE007
  • MECHANIC
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Take a looke at our vieo series for an easy and thorough way to check fuel pressure.
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Saturday, May 3rd, 2008 AT 2:08 PM
Tiny
LEGITIMATE007
  • MECHANIC
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Here you go:

https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
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Saturday, May 3rd, 2008 AT 2:09 PM
Tiny
MARKAU
  • MEMBER
  • 2 POSTS
I need to purchase a fuel gauge that has the correct fitting to thread into to the banjo bolt on either my fuel filter or fuel rail. I will then test and report my findings.
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Tuesday, May 6th, 2008 AT 9:14 PM
Tiny
LEGITIMATE007
  • MECHANIC
  • 5,121 POSTS
Be sure to do that so that we can figure this out
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Friday, May 9th, 2008 AT 9:32 PM
Tiny
RNGR8289
  • MEMBER
  • 1 POST
  • 1999 HONDA CIVIC
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 109,000 MILES
New plugs, wires, dist cap and rotor. Engine idles fine cold or hot, in gear or park, until AC compressor comes on. Problem not noticeable until engine warms up. In Park engine hot RPM s around 800 to 900, when AC comes on RPMs drop to 400 with rough idle. In Drive at stop AC will drag idle down to where the engine feels as though it will stall if not taken out of gear, or turn off AC.

Thanks in advance for the help
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Hi Rngr8289,

Seems to be a problem with the IAC and throttle body.

Idle rpm should be 770 with or without AC. Is the CEL showing?

I would suggest cleaning the throttle body and IAC and readjusting the idle speed.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
DOGFACESOLDIER07
  • MEMBER
  • 3 POSTS
  • 1999 HONDA CIVIC
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 91,000 MILES
I have had an on going problem for about 2 years now. When I first start my car and start driving at about 2000 RPM or less the engine starts to stutter/stumble and act like it is going to die, but after applying a little more gas it evens out and doesn't do it again until I stop it and start the car again. I have taken it to many shops over that time and they have no clue as to what the problem could be, and after scanning my car when the engine light came on I got trouble codes for the Idle Air Control system. After troubleshooting that down to the actual IAC valve, I replaced the valve and reset my codes, but the car was still stumbling. I have performed a full tune up of my car and still it stumbles. I am at a loss of what the problem could be now, I have explained this to a few mechanics and they told me to get my engine vacuum tested, so I did that and it was fine. They also said it could be my MAP sensor, but I haven't really done anything about that because I can't apply vacuum to the sensor to test it. If you have any clue as to anything else that I should check it would be great. But like I said I'm not showing any trouble codes and my check engine light is not lit.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
KHLOW2008
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Hi dogfacesoldier07,

Disconnect the EGR vacumn line and test if the problem goes away.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
DOGFACESOLDIER07
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My Civic doesn't have an EGR valve, I have the D16Y7 motor with automatic tranny. Anything else I could try?
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Hi dogfacesoldier07,

You need to get onto a diagnostic with the necessary tools to check the following
1. Throttle posistion sensor.
2. Fuel pressure.
3. O2 sensor.
4. Spark plugs and cables.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
DOGFACESOLDIER07
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I know already that my Primary O2 Sensor is bad, I already have one on order, it should be here later this week, but in the mean time I will check the others out as well.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
SRTYSON
  • MEMBER
  • 1 POST
  • 1998 HONDA CIVIC
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 80,000 MILES
My daughters 1998 Honda Civic idles very rough. It starts fine, then the RPMs increase to about 1/4 throttle. In Neutral the engine RPMs goe up and down consistently and the car "bucks" when accelerating in 1st gear. I was told possible the idle control sensor? Have not been able to get it resolved. Now the "engine" light comes on but the code says "engine sensor". Any help?
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
MLAB
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  • 1 POST
Hi, I know this thread ended a long time ago but I happen to have the exact same symptoms on my 99 Civic DX (manual). I'd like to know if you finally solved the problem and what you found were the causes.
I think it's the O2 sensor, but I would like to know what you found.

Thanks
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
KHLOW2008
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Hi srtyson,

What is the exact trouble code retrieved?

Erratic idling are usually caused by the Idle Air Control valve.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
~KAT
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I'm having the same problem with my 1998 Honda Civic HX. The code is P0519. It's been suggested that the Idle Control Valve be replaced, but since that part is over $200 - got any suggestions at a repair? Maybe some maintenance / cleaning that could be done before resorting to replacing the part?

Thanks!
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
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Hi Kat,

You can try cleaning the IAC and checking if the wire connectors are clean and secure.

Actually the code could be worse news, the PCM might be fried if the IAC is shorted. Seen a few of them so replacing the IAC might not be sufficient. You should be able to get the parts cheaper from the junkyard.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
TCHIEN69
  • MEMBER
  • 2 POSTS
  • 1998 HONDA CIVIC
  • 4 CYL
  • FWD
  • MANUAL
  • 150,000 MILES
When I'm idling and the A/C button (not just fan) is on, withing a few seconds, I start hearing clicking noises from the engine corresponding to sharp drops in engine rpm (so much so that I fear a stall), but it jumps right back up and repeats. Toggling the A/C button off immediately stops this behavior, but turning it back on restarts it. This used to happen sporadically, but now happens almost all the time when idling. Thanks.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Hi tchien69,

Was any repairs carried out prior to this happening?

What is the idling speed?

Are both cooling fans working?
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+2
Monday, June 1st, 2020 AT 1:27 PM (Merged)
Tiny
TCHIEN69
  • MEMBER
  • 2 POSTS
Thanks for replying. Sorry, for the late response. I'm been waiting for it to happen again so I can answer your questions more accurately, but miraculously it hasn't! I'm wondering if it only happens when the outside temp is above a certain level. I know the weather's been cooler in Dallas, TX since I posted (high's of mid-low 90's vs. High 90's / low 100's).

1. No repairs.

2. The markings aren't very detailed below 1 k RPM, but I'd say usu. 0.5-0.7 k RPM.

3. In general or during the rough idles? As far as I know, they're working in general. I know the engine temp stays constantly right at the middle of the gauge with no noticeable variance once the car's warmed up regardless of outside temps.

I'll update if it happens again.
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Monday, June 1st, 2020 AT 1:27 PM (Merged)

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