A/c and Idle quality

David_H · #1 (**permalink**) 08-03-2010, 02:16 AM

I don't know if this is something the unit will learn away or not....

With the a/c on when ever I come to a stop or just rev the engine when it comes back down to a idle it almost stalls then it recovers and idles normal. What could be wrong?

idle set at 750RPM with out a/c and it idles at 750 no problem...
idles between 750-800 with the a/c on and like I said if I burp the throttle or just push in the clutch while coming to a stop the idle drops as low as 400rpm then jumps back up hits 900-1000 then settles in around 750-800....

SoCal · #2 (**permalink**) 08-03-2010, 11:19 AM

You could check the IAC reading on the live data screens with the A/C on. Then do what you are doing that makes the idle dip. See how high IAC goes. 180 is it's max. If you are close to that - or even if you aren't - cracking the blades open a little more might help. (remember to re-calibrate the TPS afterwards.) A finite amount of air can go through the IAC circuit. Letting more of the engine's normal idling air requirement come through the blades means more of the IAC's range is held in reserve - possibly helping in a situation like yours.

You could also set your regular idle speed a little higher (target in handheld, throttle blade adjustment) so if idle dips, you would have a little more cushion before it got too low.

David_H · #3 (**permalink**) 08-03-2010, 11:40 AM

As I was falling a sleep last night it came to me that if I re adjusted the throttle screw so it doesn't close that much should sove it...

I'll look at those readings and readjust it and see what happens....Thanks....

David_H · #4 (**permalink**) 08-04-2010, 02:06 AM

Ok I checked the IAC and it was pegged at 180 the whole time the A/C was on so I re adjusted the idle screw. Now with the a/c on the IAC is around 10. I shut the A/c off and its down to 5 is this ok or should I try for 20 during idle?

the problem is almost completely gone now I can crack the throttle and it goes to a normal idle almost every time. it will still 1 out of 5 times drop for a second. right now it idles around 800rpm with the A/C on and when it does its thing it will drop down to about 650 700 then almost immediately it shoots past 800 for a split second then settles in at 800RPM???
Any thoughts or suggestions?

Oh yah the IAC reading when thats going on now is around 80 now...

SoCal · #5 (**permalink**) 08-04-2010, 01:41 PM

The only real issue with having the IAC at 5 (which is it's most closed position) is that it can't do anything more to slow the engine down. If you're fine with how it is idling, I wouldn't bother to mess with it. It doesn't have to be right at 20.

If it is just sometimes dropping 100-150 RPM, I think I'd be OK with that. The idle speed control is a closed loop function just like the fuel control. It sees something happen (like RPM dropping below the target speed because of a change in load or whatever), makes an adjustment (opens or closes IAC valve), watches what happens (RPM still dropping, dropping slower, RPM increasing, whatever), makes another adjustment, watches what happens, etc., etc.... This all happens very quickly. But not instantaneously since it takes time for each adjustment to affect engine speed. So a small degree of lag or overshoot is not uncommon.

Standard disclaimer - keep in mind that timing can affect things, too. May not be related here. Just something to keep in the back of your mind.

David_H · #6 (**permalink**) 08-08-2010, 03:15 AM

Problem solved.... re calibrated TBS set idle @ 800rpms timing is set at 15*int. ran the heck out of it.. when I come to a stop the idle only changes when the compressor cycles thats it.... I originally had the idle set down to 750 RPM and it just doesn't like it that low I guess as it is real unstable when the a/c is on....