First post here, I am very excited!

BTW, I am a super car noob with a super car problem.
I would appreciate any help I can get.

My wifes Honda Civic DX 1999, w/ 120k miles, recently had the "check engine light" turn on.

Took it to my mechanic--who specializes in Japanese cars--and he found several misfires. He changed the spark plugs and the wires, which solved the misfiring problem. He showed me there was a new reading of a P0505, and that the car was idling at 1000rpm and the check engine light was still on.

He suggested replacing the IACV--which is expensive--and said it's only a 50/50 shot it will fix the problem. From my research it could be anything from the cooling system, gasket leak, throttle cable too tight, vacuum leak, throttle body stop screw, the TPS sensor or the IACV.

Cars in the shop right now. Wifes using a rent a car, but she needs the Honda for driving to work.

Any ideas? Is 1000rpm bad? Should I have my mechanic check for other solutions before just replacing the IACV?

Thanks guys!

 

Yes there are lots of other things that can cause that which need to be checked first. I think there is also a fast idle control valve on that model which can go bad or get broken.

 

Your engine does not have a fast idle valve.

There is a logical test to figure out whether code P0505 is caused by a vacuum/intake air leak versus a faulty IACV:

Remove the air intake and then, with the engine idling, cover the hole inside the throttle body leading to the IACV with your finger. If the idle speed does not change/drop, then you have an intake air/vacuum leak. If the idle speed does change/drop, then try to adjust the idle speed down with the idle screw. If that doesn't work, then replace the IACV.

 

@MK378
Yes there are lots of other things that can cause that which need to be checked first. I think there is also a fast idle control valve on that model which can go bad or get broken.

My mechanic tried several possible solutions...checking for gasket or vacuum leaks, adjusting the TB stop screw and many other things I've most likely never thought of.

@RonJ
Your engine does not have a fast idle valve.

There is a logical test to figure out whether code P0505 is caused by a vacuum/intake air leak versus a faulty IACV:

Remove the air intake and then, with the engine idling, cover the hole inside the throttle body leading to the IACV with your finger. If the idle speed does not change/drop, then you have an intake air/vacuum leak. If the idle speed does change/drop, then try to adjust the idle speed down with the idle screw. If that doesn't work, then replace the IACV.

My mechanic checked for leaks, and decided the IACV could be the culprit. I got the car today--with the new IACV--and he may now think it's the head gasket under the fourth spark plug. It's over a grand to fix, and will take 3-4 days or up to a week to fix! Regardless, the car drives pretty good, but the check engine light still stays on. He recommended that I test drive it for a few weeks/months and to look out for any signs of smoke, or harsh idling. I guess I'll do that.

Does the head gasket sound about right? After the new IACV didn't work?
Thanks for your suggestions and advice.

 

Given that a new IACV did not result in a fix, then there must be a leak. A bad head gasket would NOT throw code P0505. A bad gasket on the throttle body or intake manifold could. Also check for a disconnected or leaking vacuum hose. Charging $1000 to fix such a problem is absolutely ridiculous. Go to another (better) mechanic. In support of the incompetence of your current mechanic, he did not have to replace the IACV to figure out that it was good. The test I described in my earlier post would have shown that P0505 was caused by a vacuum/intake air leak.

 

@RonJ
Given that a new IACV did not result in a fix, then there must be a leak. A bad head gasket would NOT throw code P0505. A bad gasket on the throttle body or intake manifold could. Also check for a disconnected or leaking vacuum hose. Charging $1000 to fix such a problem is absolutely ridiculous. Go to another (better) mechanic. In support of the incompetence of your current mechanic, he did not have to replace the IACV to figure out that it was good. The test I described in my earlier post would have shown that P0505 was caused by a vacuum/intake air leak.


You may be right. I'm taking it to a new mechanic. I will mention what you've described (vacuum/intake air leak) as a possible source of the problem.

Thanks again,

 

hell if you want to replace the head gasket drive to my house and Ill do it for 300 bucks a 6 pack of bud light and about three hours of your time!

just kidding...



good luck with your car