My 1999 RX 300 sees to have a problematic IACV. Very low idle when cold starting. After 30+ seconds, it idles well, and the problem disappears. I searched several threads and cleaned the valve with carb cleaner. Even before cleaning it though, the valve seemed to rotate freely, but I cleaned it anyway.

The problem has not gone away at cold start. What I tried next was to leave the electrical cover off of the valve, thereby letting me rotate it while the car was running. By hand, I'm able to increase the cold idle as high as 2000 rpm. To my mind, this would suggest that the mechanical part of the valve is working, but possibly the electrical control mechanism is not?

Does this sound familiar to anyone? Is there a way to test the electrical side of this? I hate to blindly purchase a new valve (and do all of that work) if I'm not fairly certain it will fix anything.

Thanks for any advice...

 

Just wanted to post an update...

I put in a brand new IAC valve yesterday. Did my first cold start this morning, and I'm still having the initial cold start idle problem!!!

Here's the scenario:
Start car without touching the gas pedal
Car starts and holds a decent idle (1,000 rpm)
Wait about 10-15 seconds, then put car into drive
Engine stumbles immediately, dropping as low as 300-400 rpm (sometimes will die)
Without intervention, engine will struggle to maintain 500 rpm (while still in drive)
If I go back to park, idle increases to near 1000 rpm.
If I let the engine idle for another 30 seconds to a minute, idle is strong and I can put car into drive (rpm around 700)

After the engine has been running for at least a minute (in park), idle is around 1500, then slowly begins dropping on it's own
over the next few minutes (as I would expect).

Once the whole warm-up scenario is gone through, the car runs great in all conditions.

Do you guys have any thoughts on other culprits, now that the IACV has been replaced? One note, my instrument panel indicates that I'm getting about 14 mpg. That's a long-term city/highway number. Is it possible that something else is going on? Car seems to idle and run smoothly. I did just replace a bad coil last month.

Not sure what to think? Thanks for any suggestions...

 

Have you tried to clean the MAF sensor on the airbox? And then reset the ECU. It may act funny till the system re-learns.

 

That reminds me that I had a new MAF sensor installed about 4 months ago! It's possible that this problem has been happening since then! I'll reset the ECU and report back. Thanks for the tip!!!

 

Wanted to report back on my cold idle issue. I mentioned previously that I replaced my IACV, and didn't really notice any noteworthy changes to my car's idling problem. I went ahead and removed/reinstalled the ECU fuse as suggested by hypervish. Right away the cold idle was better...but still not perfect. Then I remembered he mentioned that the system would need to re-learn. Over the past several days, it has gotten better and better. I would say it's as good now as I ever remember it being! So thanks to everyone who followed this thread and especially thank you to hypervish!

 

Awesome, glad to hear it's gotten better! You're welcome!