Hi everyone, I'm driving a Honda Jazz GD1 (CVT) and mileage is about 62k miles. I bought this car used and it's been doing fine for a month, than it started to have this rpm drop issue.

Initially it was fixed by cleaning the Throttle body + a used Idle Air Control Valve.

Local mechanic told me he modified the IACV (was told by other mechanic that it can't be done, but i'm guessing he played with the IACV sensor) to make the idle rpm more stable.

As the rpm was rock stable, very stable not even a slight drop so i wasn't bothered by what modification he did to the IACV.

But than another month of driving the rpm drop came back again and now no matter what i tried, i just can't fix it.

Here is the issue, every time i move off from stationary or stop at a stop line, my RPM will drop to 500 (shuttering like almost stall), and go back to 750. This only happened on cold start to maybe 30min of driving.

It might fix itself if i drive it for more than 30min - 1hour. Quickest way to fix this issue, is drive in the highway for 15min. Instant fix!

Here are the things i have tried:

1. Already change 2 set of spark plug (previously using brisk copper, now on Denso Iridium)
2. Cleaned my Throttle body + Idle Air Control Valve
3. Changed to a used GD3 Throttle body that came with IACV (IACV came loose, just tighten it yesterday but rpm drop still not fixed )
4. Adjusted the Valve Clearance twice

• First adjustment: within spec but to the tighter side
• Current: out of spec by 0.01" on both the intake and exhaust (Very loud tapping sound now )

Was told by my local mechanic that this will run better (loose is better than tight) as it will have some performance benefit (improve low end) but the trade off is super loud tapping sound <-- Am very uncomfortable with the tapping sound, felt like i might destroy something

As you all can see basically i have tried almost every thing, except Coilpack + clean EGR. From what i read in here and my local mechanic, normally stop/start rpm drop are not coil/egr related.

I'm really out of idea now and desperately in need of help. I thinking of changing to a new PCV tomorrow, but i doubt it will fix my issue. Hope you guys can help me out here!

 

Don't have a CVT but I suspect its your fast idle adjustment thats out. although 30 minutes is too long, during warmup youtr engine should idle at 1200 to 1500 rpm. And if its stalling on throttle shutoff there is a bellows type device that lets the throttle setytle down on the idle rather than a sudden stop whicvh intereferes with air flow badly.

 

I hope you have done the Idle Learn Procedure after each service attempt.

I cleaned my Throttle Body butterfly and neglected to do this, and my idle was all over the place. Gave it a week to learn by itself (500 miles) finally remembered to do the ILP and it's rock solid now.

++++++++++++

BTW anybody else notice that if the PCM senses any car movement, it boosts the idle a hundred or two RPM? Both our manual trans Hondas do this (CR-V and Fit).

 

How do you do the ILP?

-edit- nevermind found the link for it.