I was getting IAC counts of only 13 in gear with no AC on. I backed off my idle stop screw and got it up to 25 whiched helped smooth some of the rough idle out. With the AC the idle is smooth and the counts are higher. I read that counts close to 40 on a stock motor is where you want to be. I have tuner cat and wondering which IAC table I need to change? or is there other things to adjust for?

 

Vacuum leaks would be the most common cause of low IAC counts. Sounds like you might be treating the symptom and not the problem. You should never have to touch the idle stop screw unless you have a radical cam or aftermarket throttle body.

 

I've checked all vacuum lines and spray tested for leaks also. I even replaced some of them if I was in doubt. From my loggind it doesn't appear there's a vacuum leak either. I believe it has to do with a combination of the high humidity/temp in Florida here. It also seems to have developed after I had my PCM programmed by Bryan at PCMforless, but that could be coincidence. I also haven't ruled out that the IAC is going bad. I've cleaned it twice now and that didn't help. The idle is smooth if the AC is on or the temp/humidity is low. When the AC goes on it jumps the IAC counts up 10 steps and it idles perfect. I believe it also adds fuel when the AC is switched on, not sure on that. In January the car was fine. So are IAC counts supposed to be near 40 on a basically stock motor?

 

I always test vacuum lines with vacuum tester. Any other method can leave doubts. An intake runner leak at the gasket could cause a vacuum leak. Since age an mods can affect the counts, anything from 25-40 might be considered normal.

 

That's a good idea. I'll borrow a vacuum gauge and check it this weekend. Is there any one line or place to check that's best or should I check multiple lines. Also, what range is acceptable and do I check at cold start or warmed up. Thanks again.

 

hey shorbox..... the hose that runs from the passenger side valve cover to the top of the throttle body has alot of cracks on the side of the hose... would this cause any types of problems??
i think my iac is out as well


Mike

 

The line that runs to the TB from the valve cover is actually connected to a port that is in front of the TB blades, so it shouldn't affect IAC.

My experience with IAC counts indicates that anything in the range of 20-40 seems to work. The idea is to have some room before the valve completely closes, so it has room to move and control the idle, without bottoming out. Sounds like yours is within that range.

The IAC valve opens more when the A/C switches on, to make up for the extra load on the engine from the A/C. Since air flow is increasing, it shows up in the MAF, and the required fuel gets added.

Check for vacuum leaks at the PCV valve, the brake booster, and the gasket between the TB and intake manifold. Look at the lines to the FPR, HVAC controls, and EGR solenoid. Look very carefully at the EEC purge line from the purge solenoid to the passenger side of the TB... that line cracks like crazy. Make sure the EEC purge solenoid isn't sticking open.

 

Fred,
I checked vacuum at idle and I'm getting 21 or so on the gauge. I checked it in a few spots. Goes up as I revved it up, maxing it out at 30. I replaced some lines already like the elbow from the purge solenoid like you stated. So it looks to be fine. My question is; how do I check the purge solenoid to make sure it's working. I unhooked the return line and there was no vacuum at all, even revving it up, so I believe it's closed. How do I check to make sure it opens, or is that not important? I unhooked the electrical connector and that didn't open it either.
Thanks