Idle Surge p1509

[keeno]

I'm sorry for the double post but somehow I posted in the wrong section so here goes...I have a 99 civic Si 1.6. The idle surges from 1-1.5krpm. On the scanner TPS reads 9.8% throttle at 0, and does not register anything upon application until 30%. At WOT, reads only 90%. The car surges even when driving, really bad around town. I replaced the TBI with a known good unit and no change. New unit was complete with TPS, IAC, and MAP. I verified no vacuum leaks as well as cleaned all grounds engine to body. This one has me stumped so anything would help. Cheers, Keeno

 

[keeno]

p1509

Well I spent the day today exhausting all my resources. We swapped the iac, bled the cooling system, tried the idle screw, checked for vacuum leaks.....No change. I need the wiring for a 99 civic to go any further. It has to be a wiring issue. The car has a bouncing idle 1200-1600 and dead throttle/surging. Code 1509 will not clear. Even with the car off, ignition on, the code resets immediately. I am sure somebody here has experienced this before because I have seen many threads with this issue but nobody has posted the fix. Any help would be appreciated. Cheers, Keeno

 

[domm5133]

I have the same exact problem, and I changed the iacv too didn't do anything, but this one guy keeps telling me to check if there a air pocket somewhere that throws off the sensors, idk how to do that do why don't you give it a try and tell me if it works, would be much appriciated

 

[Black96EXNC]

I recently had the same code immediately come up several times after removing and cleaning my IAC valve. I wish I could give you a great answer but, The code instantly came up three times after I cleared it. I disconnected all sensors in and around the intake, throttle body etc. Plugged them back up reset it and its never happened again. It's been almost 6 months. I can't really explain what happened but it worked. Give it a shot. At least if it doesn't work for you it didn't cost you anything. Good luck!

 

[keeno]

Thanks for the responses. I bled the cooling system, This is done by running the engine with the rad cap off and the heat on full until the tstat opens then squeezing the lower rad hose several times to purge the system. Then you let the engine cool with the cap off and top up after it cools. It made no change on my car. I have a mt2500 scanner so I know my car has a electrical issue not a mechanical one. All my sensors are good. I need the wiring schematic for the 99 civic to proceed. Cheers.

 

[Black96EXNC]

Pick up a Haynes book.

 

[domm5133]

How dobtou know when the tstat opens?

 

[domm5133]

Alright buddy, I solved my problem, try tightinin your screw to your throttle body to lessin the air flow I just now did that and it fixed it, I can't promise the same but it's worth a try

 

[RonJ]

P1509 indicates a problem in the IACV circuit.

Does the Yel/Blk wire in the IACV connector have battery voltage to body ground when the key is in ON(II)?

Do any of the three IACV wires have an open or short?

If all above is fine, try swapping in a known good ECU.

 

[keeno]

Thanks, Ron. Just got A haynes, poor quality but I am in the process of doing the voltage checks. It is pointing to ECU failure at this time. I came to this site because I have a friend that is a member and He told me about a guy here (RON) that really knows these cars. I will complete my testing tomorrow and post results, Cheers