First, thank you HAF/members, I've been dealing with idle problems for months now with the only silver lining being what I've learned about my car in the process mainly from this resource. My problems started last December on the way to emissions testing when i came to a stop light and my car shuttered then died. I went home, reset the ECU, jumped through the hoops (drove on freeway,street,idled and what not) problems went away and i got my sticker, car sat until weather got nice a couple weeks ago and i decided I'd tackle this. I found and fixed a vacuum leak (reconnected disconnected hose), removed and cleaned carbon buildup on IAC and TB put everything back together, burped coolant until rad fan kicked in (the less bubbles the more melow the idle became) and started her up, idle sounded ok but not great and surging was gone. I decided to try the re-learn idle procedure figuring no harm could come of it but when i unplugged the iacv the idle became rough and jittery again and rpm seemed to rise instead of the engine almost dying as I've read was supposed to happen. I turned the car off, cleared the codes (p0505 was what it was throwing) and went to try again. immediately after starting the car the idle went nuts, high rpm and surging, turned the car off and checked codes again (cel was still on) p0505 is gone but now I have p1519 and p0108. Planning on testing MAP sensor with multimeter tomorrow but as i am a rookie i'm starting to worry i'm causing more problems than i'm solving. Any thoughts or help would be much appreciated.

-frustrated but determined

 

P0108 is MAP circuit high voltage
P0505 is Idle System control malfunction
P1519 is for Idle Control Valve circuit malfunction.

The wire colors going to the IACV are blk, yel/blk, and blk/blu. The Map wire colors are yel/red, grn/wht, and red/grn. On older accords it was possible to switch the electrical connectors, so verify the wire colors going to the map and iacv. Not sure if this is even possible on the 98-02s.

 

The MAP and TPS can get switched on the 5th and 6th gens but the OP would have a different issue - it would idle but be very hard to get the engine to ~1500 rpm's and forget anything above that.

I'd start with a good cleaning of the IAC. There are some electrical tests you can do on the IAC, do you have a volt meter?

 

I've got yellow/red, green/white & red/black on my map (or at least what im pretty sure is the right connecter for the map sensor) i cleaned the IAC already, sprayed with carb cleaner until carb cleaner ran out of it clear without the dirt specs that i saw when i started. the P0505 code is gone now so i'm not to worried about that. I do have a multimeter but am leaning towards replacing the MAP sensor. Why im hesitant to do that is because these codes (p1519,p0108) didn't show up until i unpluged the IACV and i don't understand why that would happen

 

Please don't take this the wrong way. As I read this you have no codes until you unplug the IAC?

If you leave everything alone, do you get any codes?

 

Sorry, i probably wasn't clear. this particular problem (codes p1519 & p0108) appeared when i unplugged the iac as instructed for idle re-learn process. Just went outside to check again... all sensors i can see are plugged in (iac,map,tb) . started car just now (cold engine) what im getting is no surging but at start up the rpm is in the 2k-2,250 range which is abnormal. Im thinking a MAP sensor change is in order, the more i read about changing them out the more I'm leaning towards it. BTW, 66 chevelle? ... nice

 

Update: Decided to reset ECU, unhooked positive terminal from battery for a minute, hooked it back up and started the car, the idle evened out around 1100 . I let the car sit with no load on the engine (depressed gas peddle, fans, radio, ect.) for 15 minutes then shut it off. turned it back on a minute later and the surging idle came back along with the p0505 code, codes p1519 & p0108 are gone though. Did I reset the computer right? does this indicate I should try adjusting the idle screw on the TB? Also, the car only seems to have a surging idle when in Park, D4/D3/2/1/R all idle at around 1100 rpm when in gear and braking.

 

you need to find the vacuum leak after warming the car up fully using carb cleaner and gently spraying around the intake until the idle changes .. if you cant find it it could be a bad iacv

also on obd2 cars you have to use a scanner to clear the codes you cant just pull the negative cable

 

Update: Replaced IACV with new unit (not cheap), burped coolant, disconnected battery for 30 mins to reset ECU (first cleared codes with obd2 scanner). Plugged everything back in and the idle problem was gone for 10 mintues, After the car warmed up i hit the gas and the surging came back. If i unplug the IAC while the car is running the rpms drop a little but the surging is still there, just a little faster. I was going to do the reset idle procedure but am hesitant to mess with the idle screw on the TB while the surging is happening... is that something i should worry about? Anyone have any ideas?

 

Surging when the IACV is unplugged sounds like a vacuum leak?

Look through the base-idle thread for other things...
Throttle cable slack? It must not hold the throttle open.
Throttle actually closes fully? Mechanical stop screw is only to prevent wedging stuck closed.
Vacuum leaks?