joshuajames7909

im troubleshooting my recently purchased 5 spd 99 honda civic ex and when i scanned a few weeks ago i came up with 3 codes
p0505 idle air control
p0430 catalyst system bank 2
p0420 bank 1

so around approx 1500 rpm engine pulses erratically (i can hold slight pressure on the gas in neutral and watch the needle bounce for hours) but ive been able to drive if i keep it over that (riding the clutch to achieve this). outside of that engine speed releasing and reapplying pressure to the throttle produces a violent jerk. i talked to a friend and he recommended cleaning the idle air control valve. did so and it worked ok, for about a day. i replaced it with a new one a couple days ago and today it happened again. ive read through a bunch of similar threads and listened to several different suggestions and im beginning to realize im in over my head on this problem. ive already spent about 1900 on this car since i bought it a couple months and i cant just keep throwing parts at this car.. if any other info would help ill gladly answer and i would greatly appreciate any help

0go-part

http://www.p0420.com/

http://www.obd-codes.com/p0430

You may have a clogged cat causing misfiring at idle.

joshuajames7909

it idles and drives fine for about 10 mins before that starts to happen. the catalytic conv may be bad but the 2 links for those codes suggested that they more than likely should not effect driveability and its becoming increasingly impossible to drive more than a few miles

beecee18

would help to know what vehicle OP is troubleshooting.

P0430 is the same as P0420 only difference is the bank the fault is located at.
4 cyl do not have more then one bank of cylinders so forget that code and pay attention to P0420 and mostly P0505 which is the idle air control valve.
Fixing the P0505 will fix the catalyst code (P0420) as P0505 tends to cause a rich condition that upsets catalyst efficiency

Clean IACV first and reinstall and reset ECU and check for codes to reappear. If they do you will need to replace the IACV. letting us know when these codes arrive after ECU reset will help also, instantly, 1-2 trips, etc.

There is no misfire, and the cat is most likely ok unless you keep loading it up driving around with the rich condition caused by P0505

Nice try though^

beecee18

You are correct P04xx does not affect how the car drives, fuels, etc.

P0505 is what is causing all of your problems, it must be defeated first.

joshuajames7909

thanks i just replaced the iacv last week but i never thought to reset the ecu. ill do that first thing tomorrow and go for a drive to see if any codes come back. ill be sure to let you know what happens

and as i forgot to mention the vehicle info in the original post, its a 5 speed 99 honda civic EX with approx 158k

joshuajames7909

i was also considering cleaning out the throttle body with a rag and carb cleaner but if it were a tps issue it would definitely trip a tps engine code right?

joshuajames7909

just to update I put about 45 miles on the car, in the course of about 4 trips, and the light came back on and repeated the same symptoms. I went down to advance auto to scan it and it had the same 3 codes as before, but the p0505 code showed up 3 separate times but I'm not sure why. not sure what to do at this point

Former User

Check for vacuum and intake air leaks. If none is found, adjust the idle speed as per service manual.

joshuajames7909

i couldnt find any leaks and when i got fed up trying i took it to a honda dealership. i waited 3 hours and they bled the coolant line, checked for vacuum leaks, and cleaned what they defined as a small amount of carbon out of one of the lines on the throttle body. apparently that made the code go away so they stopped. a week later it came back ive been continuing to seek a means to an end. any other triggers for that code?