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I have a stock 99 EX and recently it's developed the p0505 issue. I've seen this on many threads but none of them seem to come to a conclusion, so I'm looking for help!

At around approx 1500 rpm engine pulses erratically with throttle pressure, and releasing and reapplying pressure to the throttle while driving produces a violent jerk. The car will buck if you are in that 1500-1700 rpm range. This only happens when the car is at operating temperature.

1. Sitting at a light, the idle will suddenly rise about 400
2. Cel will immediatly come
3. What I described above will happen

If I clear the cel while driving the issue suddenly goes away but will come back a day or 2 later. So far I've checked for vacuum leaks and cleaned the iacv, but that only worked for a few days. Please help!!! I have a scanner that shows some live data if that helps!

Ps: car also has p0420 which is a cat code and is probably unrelated FYI

 
Rep Power: 519

Vacuum leaks? Cruise vac hose off?
IAC sticking?

Is it a rotary type IAC valve (auto trans car)?

 
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I did my best to look for vacuum leaks but didn't see any noticeable ones..I checked the cruise vacuum hose that attaches to the nipple and it was good too. The iacv looks nice and clean now, are there any tests you can do on it? The car is a manual 5 speed

 
Rep Power: 519

So your IAC should be a plunger type bolted to the back of the intake manifold? (#9)





Pull the intake snorkel off the throttle body while it is surging.
You should see ....maybe 2 ports in there. Plug off the open ports inside the throttle body with your fingers.
Which port makes the most difference? Any difference?
What does the engine do when you plug it off? Does it die, almost die, or idle at the right speed?

Tap on it with a screwdriver handle or tiny hammer (not hard enough to dent the aluminum!) and see if that changes anything.


What does the idle speed do when you unplug the wires from the IAC valve?

 
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Thanks for the help! Ill try this soon and get back to you! Should I plug both holes at once, or 1 at a time? One time when this was going on I unplugged the iacv and if I remember correctly the high idle and surging stopped and the rpms dropped and stayed steady at about 1100rpms (still high). Ill test again thanks!