1999 honda accord 55k miles engine idle surges from aprox 1000-2000 when in park. I have replaced the iac valve and cleaned throttle body. Any ideas where I should poke around next

 

Set the "base idle". There's a post by me in the DIY area here, with the method. It's not simply adjusting the idle.

 

My idle surging was cause by air in the cooling system.
After bleeding out the air it stopped.

 

the idle is no longer surging but it is some times high when warm seams kind of random some times it is right around 1k, and some time when I'm driving it will feel like its not decelerating and I'l put it in neutral and the idle is at 1.6-1.8. every once and a while it will fall down just below 1k and then come back up to 1.75 or so and pretty much stay there.

 

This is after you set your base idle & forced the ECU to re-learn??

 

I closed your other thread so everything is in one place - I think that's less confusing.

You ask about a temperature sensor. Yes there IS a temperature sensor that can cause something like this. Below your distributor is a 2-wire sensor and a 1-wire sensor. The 1-wire sensor drives the gauge in your cluster and the 2-wire sensor is for the engine-control computer. Look for loose/dirty/corroded wiring connections.

When this sensor sees air instead of liquid, that's one way for air in the cooling system to confuse the idle-control system.

Otherwise the proper way to test that 2-wire sensor is put it in a pot of water with a thermometer and hooked up to a multi-meter to measure resistance in ohms. A shop manual will have a table of resistance at various temperatures for you to check at.

 

I haven't yet set base idle, I think I warm car till fan comes on then shut down and unplug iacv and then set base idle correct? how do i force cpu to recognize this?

 

Read about it in here.

https://www.hondaaccordforum.com/for...e-speed-38734/

 

I saw your message but it's best to do this in the board, not in private. That way you get other people smarter than me to help out too.

You said your idle goes high & erratic when you unplug your IACV.

I'd look for vacuum leaks. Then I'd make sure the idle stop screw or throttle cable aren't holding open the throttle plate. Some misguided former mechanic might have tried those things to increase the idle RPM. It's good you found that rather than just trying to bandaid the problem any further.

 

I replaced vacum lines still same problem. I think it might be the egr valve. I did a continuity test between 1 and 2 terminals 1.3k and 2 and 3 terminals 4.5k plunger functions properly I hooked jumpers to 4 and 6 to battery and egr valve closed started engine barely idled but ran still. also idle screw is all the way in

I set base idle and forced CPU to recognize. Also checked for vacuum links with propane and carb cleaner all around throtle body and injectors. I'm stumped here, I'm wondering if it is something to do with the fuel pressure regulator.

When I idle the car it idles fine right around 800 "note idle screw is all the way screwed down" after driving for a minute with load if i put the car in neutral the idle will go up to 1500 and very slowly go down.