Error code: P0303 & P0505

[gnailuh]

ok, 84K miles and check engine light never came on, and now i just finished all kinds of maintenance and the check engine light comes on. i recently cleaned the throttle body and the dealer just changed my timing belt. according to the scan too i borrowed:

P0303 - Cylinder #3 misfire
P0505 - Idle air control motor circuit malfunction

after the throttle body cleaning, the car is running great as ever. and idles nicely at 750/800 rpm. i did have unplug the iac connector to clean the throttle body, but that was a week ago. but i dealer did change my timing belt and the check engine light came on 2 days later... any relations you think?

if my car is running and idling perfectly, should i even worry? how can i check to see if cylinder #3 is actually misfiring? the plug wire is fine and the plug looks great. should i just erase the code and see if it comes back on in a few days or weeks?

any suggestions would be greatly appreciated.

thanks!

[ashah000]

If cyl. 3 is misfiring you should feel it, even if it is the slightest jerk.

Take the negative cable off your battery and see if the CEL comes back on, if so then goto autozone and get them to read your codes again, and see what comes up.

[kjewer1]

When you reconnect the battery after clearing the codes (assuming you dont have a datalogger, if you do disonnect the battery anwyway) be sure the ISC is plugged in (was it last time?). The ECU has no closed loop control over the position of the ISC motor, so when you power cycle the ECU it will move the ISC motor into a hard stop past its limits. You'll hear it clicking. It then knows it must be at one side of its travel, and it will be if its connected and functioning, then move it to the center. This is how it synchronizes itself with the ISC motor. If you power up the battery with the ISC disconnected it wil be out of synch with the ecu and you can get a trouble code for it.

Not sure if this is the case for you, but its an easy thing to do before lookng further. And if the car is idling properly with the ISC plugged in, chances are the ISC itself is fine

For the misfire DTC, do like ashah mentioned above and just clear it and see if it comes back. If it does somthing is wrong. I dont know what you could screw up in a tbelt job that would cause it, but I would certainly take it back to the dealer and let them know that the first instance of this code was 2 days after the work they did.

[gnailuh]

ok, here's the deal. like i said before, the car runs like a champ... so noway there could be a misfire. i have the scan tool on loan from autozone (free by the way for 90 days!). so i cleared the codes and drove it around a bit...

... well, the light came back on again. this time, the cylinder 3 misfire is gone. but it still showed 2 codes, P0505 (idle air control motor) and P0505 again... what's up with that? the only difference is that on the second P0505, there's a small little pd symbol on the right most part of the scanner display. it's a OBD II AutoScanner. the manual says something about MIL (malfunction indicator lamp) and the "pending" status. not sure what that means... any ideas?

it idles just fine... 95GSXRacer, i did not disconnect the battery when unplugging the ISC connector to clean the throttle body... is resetting the code with the scanner the same as removing the battery connector? should i try diconnecting the battery? and how long should i have it disconnected for?

thanks again.

[ashah000]

Originally Posted by gnailuh

ok, here's the deal. like i said before, the car runs like a champ... so noway there could be a misfire. i have the scan tool on loan from autozone (free by the way for 90 days!). so i cleared the codes and drove it around a bit...

Wait they loan the scanners out.
Hey when you use it, do you turn the car on all the way, or just to the acc. position. Because last time I went to autozone the scanner said "Linking Error"

As far as I know the scanner does not "reset" it, it actually erases the code. The battery terminal doesn't clear it, it just resets it.

[gnailuh]

Yes, loan/rent. You basically pay for it, then they refund you the money. They do this in hope that once you find the problem, you'll buy the part from them.

So what the hell is the diff between "erase" and "reset"? Which one do I want?

THanks.

[ashah000]

I believe this is how it works...
Reset - No CEL, codes are still stored in the ecu
Erase - erase the codes, taken out of the ecu.

You can erase or reset it doesn't matter. But if you have the tool to erase it, I would.

BTW what position do you use it in(acc, car fully on) Thanks

[gnailuh]

The manual says to put the car in the full On position. I never tried the acc position, but with the car off, the scanner has power, but I get the "Link Error". So full On seems to be the right way.

[ashah000]

Damn so something is wrong with my car. I think I had too many codes, so the damn scanner gave me link error.

[kjewer1]

ok, here's the deal. like i said before, the car runs like a champ... so noway there could be a misfire.

Your ass isnt calibrated well enough to detect single cycle misfires. Thats why we have all of this expensive and complicated onboard diagnostic BS...

95GSXRacer, i did not disconnect the battery when unplugging the ISC connector to clean the throttle body... is resetting the code with the scanner the same as removing the battery connector? should i try diconnecting the battery? and how long should i have it disconnected for?

Yes, you should disconnect it, as I said here:

When you reconnect the battery after clearing the codes (assuming you dont have a datalogger, if you do disonnect the battery anwyway)

Jsut to resynch the ISC motor. Only needs about 30 seconds. Again, if it was really bad you would probably know. If you want to you can do some of the typical tests on the ISC, like checing the resistance between the coils. See the vfaqs, www.crebotech.com, and google for how to do it.

Key must be in the on position. ECU doesnt come on in ACC position so you cant connect to it.

Clearing the codes is the only way to turn off the CEL/MIL (check engine light/malfucntion idicator lamp), and that will remove the code from memory. Disconnecting the battery will wipe out all the codes and clear the light as well, but will also reset everything else, like fuel trims, ISC learned idle position, etc.

I dont think you can have too many codes and get an error from teh tool. That wouldnt make much sense if it was setup that way Not all OBDII scanners are the same. OBDII loggers for example may work on imports but not work on domestics, and vice versa. I would expect scan tools to all be interchangeable though. Do they offer more than one type?

[soyee7]

My car makes a cliking noise that sounds like its comming from the intake when i step on the trottle past a certain point, could this be my ISC? So to reset the isc i need to turn the car off, position the isc to the middle, then connect the isc, and then turn the car back on. Right?

[kjewer1]

Turn the car off. Disconnect the battery. Wait a minute. Reconnect it. Turn the key to the on position. You should hear it vibrate for a second. Its now reset. Thats it. If your ISC was bad you wouldnt be able to hold a steady idle all the time. The noise you mention doesnt tell me the ISC is bad..

[soyee7]

what would the idle be like if the isc was bad?

[kjewer1]

It would surge or hunt. Check out the vfaqs for the idle surge problem. TONS of info in there. www.crebotech.com has a bunch of info as well IIRC.

[soyee7]

thanx