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Old 08-19-2010, 07:43 PM   #1
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Installed new carb insulator= slightly higher idle?

I put a new carburetor insulator, & talked myself out of having my carburetor rebuilt as i get 40mpg with this car.

So I used carb spray to clean, and checked all the vacuum ports & functioned checked the vacuum controls with a hand pump.
I got the car back together and I'm 99% sure the vacuum hoses are correct.
But the idle is a bit higher than when I started ~900 going by my factory tac.
The thing that I notice it how much the idle varies when the fan kicks on.

I think I'll use some propane to check for vacuum leaks just in case I missed something or split one.

I'd like an opinion if you think this could be a normal condition after fixing my leaking carburetor insulator?
My thought is the previous owners mechanic could have adjusted the idle to compensate for the vac. leak before I got it.
Anyone experience this before?
s/t
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Old 08-19-2010, 07:47 PM   #2
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Re: Installed new carb insulator= slightly higher idle?

I'm thinking the carb was adjusted to compensate for the vacuum leak. Readjust your idle speed.
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Old 08-21-2010, 06:35 PM   #3
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Re: Installed new carb insulator= slightly higher idle?

It is very common for people to try to increase the idle speed to make up for an intermittent miss that allows the car to stall under certain conditions.

Was the rubber carb insulator cracked when you removed it? If so, you probably did have a vacuum leak and were running a little bit lean.

I would just lower the idle speed by turning the adjusting screw.
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Old 08-22-2010, 07:31 AM   #4
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Re: Installed new carb insulator= slightly higher idle?

I third the advice so far. I've seen many instances of a PO or mechanic (especially family mechanics) adjusting things to compensate for a problem (even in brakes, alignment, tires which can be really scary)
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Old 08-22-2010, 08:27 AM   #5
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Re: Installed new carb insulator= slightly higher idle?

Quote:
Originally Posted by Erik View Post
It is very common for people to try to increase the idle speed to make up for an intermittent miss that allows the car to stall under certain conditions.

Was the rubber carb insulator cracked when you removed it? If so, you probably did have a vacuum leak and were running a little bit lean.

I would just lower the idle speed by turning the adjusting screw.
The insulator had fairly large cracks on the sides. I could see any evidence of them reaching into the intake area though. The seal was hard and I suspected it was leaking there instead.
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Old 08-22-2010, 08:43 AM   #6
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Re: Installed new carb insulator= slightly higher idle?

Update. I turned the idle down and got it to the 750rpm (factory tac), and drove it to make sure she was going to stay there all was good.
Then drove down to the emissions place ~12 miles freeway + 5 miles city. She
she acted pretty good holding the 750 rpm (would slightly hunt a few rpm, with the occasional 50rpm when the fan kicked in or out).
When I pulled in the emissions place she was idling 1100~1200 rpm! I couldn't believe it.
The guy ask how it's going I said not well. The car never idled down so I backed it out and ended up turning the idle screw way out.
Sat there and it still would creep up to ~1000.

So something else is causing this.
I'm going to the dealer and get a new O2 sensor just to check it off the suspect list. Unless someone can recommend an after market one that fits.
The Bosh unit had the wrong connector.

Things I've check already.
Vacuum leaks using carb cleaner nothing noted. I'm going to remove the air cleaner and try a better job just to double check.

I have a broken sensor on the intakes air horn Not sure what it does could this be the cause of my problem?
I resides on the under side of the air horn, just behind the vacuum pot.
The two wires look intact but the rubber is torn up an it flops around in the hole.
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Old 08-22-2010, 09:07 AM   #7
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Re: Installed new carb insulator= slightly higher idle?

What kind of vehicle is this that you have a carburetor and an O2 sensor?
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Old 08-22-2010, 10:44 AM   #8
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Re: Installed new carb insulator= slightly higher idle?

It's a 1987 honda civic with the D15A2 engine.
Now If I can only find the ECU and find the codes.
I under stand they are lights on the ECU, but hadn't found anything definite for the 87 models.
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Old 08-22-2010, 11:21 AM   #9
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Re: Installed new carb insulator= slightly higher idle?

I've tried to insert a signature with vehicle, but can find the option?
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Old 08-22-2010, 12:58 PM   #10
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Re: Installed new carb insulator= slightly higher idle?

The 87 carbed civic (I drive one) has a primitive electronic control box that uses solenoids to control vacuum bleeds according to engine temp, speed, oxygen sensor values etc. There are no trouble codes that can be accessed or that are even stored by the electronic control box.

The best you can do is monitor the oxygen sensor output with a digital voltmeter and see if it averages out to 400-500 milivolts (it normally jumps around above and below these values as the air bleeds try to lean it out when it gets too rich).

You can get a universal 1 wire oxygen sensor for it at many auto parts stores and splice it into the factory wire using the materials included with the sensor (heat shrink tubing is included with the sensor)- So you just cut the wire/connector off the old sensor and add it to the new one.

The fuel injected civics/crx's of the 1984-1987 generation do have a computer that stores codes that can be retrieved.

If you have air conditioning, there is a vacuum operated idle up mechanism that bumps you up to a fast idle when the AC compressor kicks on. It is on the drivers side of the carb, toward the back. It may be bumping up your idle.

As you have noticed, there are 50+ vacuum hoses- if any of them has an intermittent leak, it can cause problems like you are describing.

Also check the fuel level in the carb- if the float level is changing because of a bad float valve, the idle speed will change too. You can check the fuel level by looking through the sight glass on the drivers side of the carb while the engine is running.
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