Honda Prelude Forum - PreludeDriver.com

Well, i noticed this after we got the car running, but at first we found out that the O2 sensor wires where just swiched and that fixed the problem. now it's back.

What it's doing is when it starts it idles at about ... 2000-2200* then it will drop to about ... 1500 and raise back up , but at a sorta quick pace . Well my first thought was the tstate so i went ahead and replaced that, figured that would fix the problem.. nope , then it though maybe being this is my first time installing a tstat i just put it in wrong... But no i was told it's in there correctly so...

Just to clarify though , the pointed end would be pointed towards the housing u take off correct?

Any ways so now im just confused as to what could be the problem.

Any ideas.. i can try my best to get a vid of it doing it but other then that i dont know what else to do.... I would much rather fix the problem myself if i can ... but if i can't then i suppose i would bring it in but first things first i would like to try..

So please post up any and all information/questions so i can get this problem fixed asap.

Chi_Town

A fluctuating idle is most often caused by the IAC valve not working correctly. This seems to happen to all Preludes at some point in their life.

The IAC valve depends on the engine coolant to activate it and work correctly. If your coolant has not been bled correctly, you will have idle problems.

For starters, I suggest that you bleed your coolant lines with the engine hot and the front of the car elevated a bit. You don't want any bubbles in your coolant lines. This is especially suspect since you have just been working with the thermostat. Did you bleed the coolant lines after changing the thermostat?

You did put the thermostat in the right way.

The bleed bolt for the coolant system is right on the front of the thermostat housing. Just run the car until it is warm (thermostat open and upper rad hose hot), then open the bleed bolt until you get fluid with no bubbles coming out. Close the bolt, and you;re done. If that doesn't fix your idle, let us know.

You'll probably find the following discussions helpful:

http://preludedriver.com/forum/viewtopic.php?t=295

http://preludedriver.com/forum/viewtopic.php?t=310