Hello, I was hoping to get some direction on where to look for a new weird idle issue I have been having. My car is fluctuating between 1-1.5k very quickly every second, it seems different from the typical IACV and Fast idle valve, I took them both apart and cleaned the IACV and checked the plastic plunger in the fast idle valve, but symptoms remain. This came out of no where after driving home last night and when pulling up to the light it was fluctuating. What else should I be looking at or anything that can cause this erratic idle when engine cold and engine is warm as well? I have tried so search but nothing seems to match as far as I can tell to similar symptoms. Would a bad TB gasket or intake manifold gasket cause such a severe idle surge?

 

If you don't have a vacuum leak, you may just need a new IACV. I recall that it took me 3 IACV's from my collection of used IACV's to find one that worked and didn't idle surge even though they all clicked when "tested".

 

okay so I was messing with it again today and the idle will return to normal if plugging the top hole inside the throttle body and nothing changes with plugging the lower. Does that mean anything or what to look for next?

 

Just replying for a possible resolution. Went to the junkyard and grabbed a IACV off a 93 civic cleaned it and had it soak with some brake cleaner for a good while then let it dry out for several hours. Slapped it in and started car without radiator cap at the same time just in case it was an air pocket in the coolant lines. Car idled down super low like 500 rpm while cold but no changes to idle. Let it idle until bottom hose got warm and thermostat opened, drove it about a mile, and so far so good. Will try again tomorrow when it is light outside. Hopefully this resolved my issue.

 

For God sake man... MAKE, MODEL, and YEAR of the car you are working on please !!! When you say you plugged the top hole inside the throttle body, I assume this means you put a finger over the hole at the 10 O'clock position and the idle returned to normal... this means that you have a BAD IACV and you must have some additional vacuum leak somewhere else, because normally when you block this hole, the idle should drop down to 450-500 RPM which is near stalling.

 

Wow my bad! 1994 Honda del sol S, 1.5l engine. Yeah covering that hole dropped it down to around 400 or so and almost stalling on the idle. So replacing it hopefully fixed my problem!

 

There you go. If the replacement IACV seemed to work fine AND the idle dropped down to 500 RPM'ish when you blocked off the 10 O'clock hole in the throttle body, it sounds like you have found the problem and fixed it for now. Well done.