I am at my wit's end with a p1509 idle air control valve circuit failure. My car is a 98 sedan with the y7. It started several months ago when I had a bad water pump leak. It began the infamous idle sure and threw a cel. I deleted my iacv by blocking it off with a plate and looping the coolant hoses together for the time being so my car would run half decent. I replaced the water pump a while back and just finally have bought a new iacv and put it on the car. I've bled the coolant system several times and have reset the ecu, I've been through the idle learn procedure, I've taken the throttle body off and cleaned it yet I can't shake this haunting p1509 and surging idle. When I first replaced the iacv, I could get the code to stay off for an hour or so and the car would run fine, but now as soon as I clear the code it comes right back no matter what I do, unplug it and plug it back, reset ecu, nothing. Please help I'm really stuck here.

 

If it helps shed any light on the situation, when I unplug the iacv with the car running it continues to idle surge, however the idle surge changes. It becomes slower and the surge becomes greater between rpms, if that makes sense. Then when I plug it back in, the idle surge changes back to the shorter surge. I have also replaced the pcv valve and few other parts that aren't really related such as speed sensor and distributor.

 

Don't start new threads about the same problem.

 

There are NO answers out there. I've researched and researched till my thumbs are blue. I have been very patient with this and been very reluctant to post. Does anybody know the circuit testing procedure for a 3 wire iacv? There is no imformation on this I can find.

 

I think he is indicating you already have a thread for this car/issue and now you are starting a 2nd thread for the same car/issue.

Is this not the case?

 

​​​It's in the service manual.

 

I don't have a service manual or the extra money to go buy one being as they are not really cheap. Does anyone know how to test the 3 wire iacv circuit? I cannot find this info ANYWHERE. I did test voltage to the 3 pins. Key on, engine off I got 10.4 volts to the middle/yellow wire and nothing on the other 2 wires. Engine on and still cold I got 14.7 volts to the middle/yellow wire and .3 volts to the other 2. I have no idea what this means though, as I can't find any info on how exactly the 3 wire iacv works, or how to test the circuit for failure. Please if anyone has any info on this please share. This is my last ditch effort before I just start throwing parts at this, starting with a new ecu.

 

Hardly anyone has the paper service manual ... they all have a scanned PDF version. Google to download off the web!!

 

You are doing basic maintenance, the information has been available online for free for more than a decade. Stop making threads and RESEARCH until you have your answer.

 

Test for p1509

 

This is EXACTLY what I needed. Thank you so much. Couldn't find this info ANYWHERE online. I have some testing to do!

 

Ok, so I went to start with the testing procedure. The first thing I did is take my ecu bolts out and sat it in the floorboard for easy access during testing. I then unplugged clip "A" from the above photo just to get a visual inspection of all the wires in the clip. I plugged the clip back into the ecu and started the engine and... Poof!.. no more idle surge. I did still have a CEL on so I hooked up my obd2 scanner and cleared the code. I been driving for 3 or 4 days now without any issues. So this must have just been a poor connection going into the ecu. I was at my wit's end with this, ready to sell the car over such a simple overlook. Anyone having issues with CEL code p1509, I would highly recommend unplugging and reconnecting your ecu from the harness. I had done almost everything mechanically related to iacv that I could, and unplugging my ecu is what finally resolved my issue. For anyone with a 3 wire iacv that this doesn't fix, the procedure for testing the circuit is above. Thanks for all the help guys! So happy ol betsy is running nice again!!!

 

Great!! The ol' systematic approach wins again! 😉

 

invest in the FSM.

 

Flying spaghetti monster? Lol. Seriously, what is FSM?

 

Factory Service Manual, also known as the Helms manual and can be purchased at helmsinc.com

Google search might turn up links to the pdf version for free, however it is getting more challenging to find as piracy is being continually whittled away on.

 

Oh yes I've already been on the hunt for one. I tried buying a PDF version when I was trouble shooting my iacv but had issues for some reason. I'd really rather have a paper back myself anyways, so I will be purchasing one soon! Thanks for the advice!