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I've searched and has done this. 1st got 505 code and misfire codes 300-303.read and cleaned the IAC valve still idle 1000-1900.tested all wires going to valve,all good.replaced valve still same idle 1000-1900.have bleed the cooling system a bunch of different.put it in gear idles good.drive it runs good.sprayed carb cleaner around intake and hoses.no difference in idle speed.put hand over throttle body engine will die if left there.blocked hole in throttle body idles fine(looks like air hole for IAC valve).any suggestions to point me in right direction.thank you.tested new valve and even old valve were in specs.

 
Rep Power: 518

What was the cause of the misfire codes? Has this issue been completely resolved yet?


Tap on IAC with a tiny hammer: does the idle speed change at all?

What transmission does the car have?
What does the idle speed do when you unplug the IAC?



Have you done the Idle relearn ---including 10 minute battery disconnect to erase memory?

 
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it's an automatic.when I unplug IAC valve idle steady.didn't look at tach to see RPM's.seemed high(1200-1500-rpm).haven't did a relearn or disconnect battery.have to do it tomorrow having high winds right now with 60 mph gusts.i did try tapping it with in of rachet.no change.i'll look up how to do a computer relearn.thank you.don't know what cause other codes.when clear codes runs great.ran fine started it after work just driving light comes on then started missing almost home.1st code was the p505 code so thought start there.newplugs(look lean) I know I need dist cap & rotor.

 
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disconnected battery for 30 minutes.did relearn.still idles 1000 to 1900.drove it and threw the p505 code again.think goin take new valve off and take a good look at it when car cools down.i did tap IAC valve with hammer too.

 
Rep Power: 518

IMO the misfire codes are more important.

This tells me the majority of excess airflow is originating from the throttle body, although there can be other issues involved.
Trouble tree says the next step should be to adjust base idle speed, and if that doesn't help then replace the IAC valve. (Or the IAC is still sticking, like it can't close all the way.)

Your IAC is on the bottom of the throttle body (correct?), but I think there should be a second hole at the top of the TB that leads to the IAB (idle air bypass) screw at the top. This is where you are supposed to adjust the base idle speed, according to the service manuals.
Something like this one:


If you block off the lower hole and the speed dropped to about normal idle.... Now block off the upper hole, does the engine speed drop even further?


How clean is your IAC valve? Is the little vane totally free and unobstructed in its movements?

Check out this thread, see how clean the poster got his IAC valve
https://www.civicforums.com/forums/3...ml#post4675982




Checked for burned spots in the ECM?


When did the problem start happening?

 
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took new IAC valve off took magnetic part off,it moves easy all clean.when i block bottom hole idles fine alittle high.then block both holes drops idle a little about right.doing this myself so can't read tach.retested valve.20.4 ohms on each side,has 12.4 volts black and yellow wire going to it.i was just driving on freeway at 55 about 3 miles after entering freeway.yes valve is at bottom ofthrottle body.when i turn the idle bypass really no change.i know i'm just missing something smiple or not doing something right.i guess next put the old one back on.it's not stuck(i cleaned it with carb cleaner) and moves free to and is in specs 20.8 ohms see what happens. it threw the misfire codes once back in 2010 when i joined this forum.cleared them and hadn't had any troble at all with this car till now.

 
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Have you checked inside the PCM for burned spots or leaking capacitors?




Just a thought.

 
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took computer out nothing like that at all.really clean inside no dust or dirt.took new valve off and when I did I seen it leaking coolant out of one of the hose connections.the new valve is leaking coolant from the pressed in tube where the hose connects to.took the magnet part put on old valve and it seems to be idling right now.Thank You for your help.great help here.

 
Rep Power: 518

Glad you got it working!

 
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well it didn't last long.threw 2 codes and both were the 505 code.then started bucking.now the idling rpm is between 1000 & 1500 instead of 1000 to 1900.had it running right yesterday.thinking I need a better scanner one that more reads than just codes.not sure what direction to go now,maybe go to wrecking yard pickup a used one.1st code isp505 then 2nd code read p505 pd.

 
Rep Power: 518

Poop. I got nuthin.

Code P0505 will set if no-load idle RPM is more than 200 above "target" (or more than 100 below target).

If you corked off all the holes in the opening of the throttle body the RPM should have dropped to ~650 or less (use a scanner to read RPM for this).
You positive there aren't any vacuum leaks?

 
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I used a can of brake clean and sprayed every vacuum hose I seen plus the intake manifold topand bottom,but I just thought to do a coolant pressure test and a found a leak at water outlet that bolts to the head.going get new gasket.checked have to order it.i got gasket material so going to make one.when I blocked off both holes really didn't drop rpm's a whole lot.didn't see tach to see how much.scannr I have just reads codes,might have to get me a xmas present a good scanner

 
Rep Power: 518

I thought you said earlier this made the RPM drop to some reasonable level?

I know you said if you cover the whole throttle body you can kill the engine.....



Here's an odd thought: How many miles on this rig? How much wear and play is there in the throttle shaft and bushings? I've seen a couple that had inconsistent weird idle probs when the shaft and bushings are worn.

 
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it drop to idle to where it sounded like where it's suppose to be now not sure where it dropped.there's 197,000 miles on it.i sprayed around the throttle body shaft.had that problem before with zenith carbs.funny thing about this I worked as a tech for a Cadillac dealership for 35 yrs.i guess you loose it when you retire.

 
Rep Power: 518

This SHOULD mean there aren't external vacuum leaks (now that I think about it) so in my mind you're down to some IAC related control problem or the TB itself ....

I don't think you'd notice anything by spraying -- without being able to watch fuel trims on a scanner.

I was thinking maybe the throttle is getting cocked crooked in the bore when vacuum is pulling on it, causing the space between blade and bore to be larger than normal.

I know many GMs did the same thing at higher mileage. Carbs and some TBI engines came to mind first, then I realize I have seen it on all sorts of the Generals products over the years. I know my GFs Saturn does it.



Throttle sticks closed when under vacuum?

Grab the cable wheel end and wiggle and pull 'away from vacuum' to see if the blade will seat tighter in the bore?

 
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I was looking at rockauto parts and they listed 2 valves 1 for CVT transmission(what I have) and one for standard trans.they have different part #'s.could this make a difference

 
Rep Power: 518

A look in my catalog at a 98 gave me 3 different IAC choices:

36450-P2J-J01, EX, HX, M/T

16022-P2A-J01, DX, M/T

16022-P2E-A51, DX, EX, HX, A/T


Yes it apparently makes a difference.

 
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ok finally fixed it.don't buy a cheap IAC valve.get one with the same part # as the one you takeoff.if I would have done that in the 1st place.if ,should have.Thank You for your help.greatly appreciated

 
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Thanks for that update. I guess that's yet another item that really needs to be factory.

 
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ok I was still having idle bounce,thought I had it fixed.it did work for a while then started up again.so I went to u-pull-it found a HX there and got a throttle body.think this did the trick.car runs better idles at 800 rpm's.idle comes down a little slow,but have to adjust TPS.reads 12.2 on scanner. when I first read TPS(when this started) it read 9.4. from what I 've read should it be 10 for HX? it sure does run good now

 
Rep Power: 518

TPS on your scanner is probably displayed in %.

I read all of mine in volts on my scanner.

0.49v at closed throttle is the norm, and that number has been damn consistent across the entire car line. (I think that's why most of the TPS have tamper resistant fasteners.)