I did search on my issue but most had erratic idle because of a part they installed. Anyway, I've had this issue before but it seldom happens until now. I've been driving around town for a few hours in 100F+ heat today. The first couple of hours, the car ran fine with the AC on. But just a few moments ago the car's idle got erratic, dropping to about 600rpm and up again to 900rpm. Everything else is fine and it only happens when there's no load (i.e. stopped in traffic) and the AC is on. Can anyone point me to what I should check for? TiA!

 

This is probably because of the extra heat the A/C condensor is creating under the hood (your engine is sucking in WAY too much hot air). Hot air will make your engine idle very low. Move somewhere colder. My DSM use to do this ALL the time. I had to re-adjust the idle every time the season changed.

 

To be clear, you have no mods?

 

Sounds like your are getting the low vaccum, which is causing some erratic behavior. I used to get this alot until I did some minor timing and fuel tuning at the low range of my map. I still get the occasional low idle bump, but the car doesnt stall anymore.

The already low vaccum that exists in a stock EVO can be exasperated by some mods though, so it is importent to know if you have any mods on your car. Especially cams, after market BOV's, etc.

 

Other than a turbo timer, I'm totally stock. Is there a way to adjust the idle rpm to compensate?

 

You can either try adjusting the BISS screw or leaving the throttle body plate slightly cocked open by adjusting the tension bracket:

https://www.evolutionm.net/forums/sh...dle+adjustment

 

I'll try that out, thanks for the info

 

If your Turbo Timer has a voltage reading, I would be interested to see if you are dropping below 12 volts with your AC on.

 

I'm not sure my tt has it but I'll check (It's a Greddy FATT unit).