I raised my A/C Ant. VS A/C Pressure counts by 10, car still wouldn't idle with A/C on. Raised the counts 10 more, and it will idle, but a little rough. Tomorrow I will raise the counts by 5 more, think this will get me where I need to be.

Why do these cars run so bad with the a/c on. I have never had a car that the a/c sucks the low end power like this Vette. I can't even tell the a/c is on in my truck.

 

Does your truck have a big cam though?

My car did fine with the 305 cam which is 220/230 I think but since I've went to this 230/242 it doesn't like the a/c nearly as well.

 

No, but it has 425rwhp/503rwtq.

Even when my Vette was stock. I didn't like the way it ran with the A/C on.

 

that camshaft soaks up the power.. at a idle and a cam in the 220/230 range your talking about 30% less cylinder pressure at idle at least.

 

Interesting topic- I been having a similar problem with my hot cam'd LT4...the car will idle round 400-500 with a/c on in open loop, however as soon as it enters in closed loop the idle jumps back up to 950 where it should be. I have LT1 edit so I my play around with those IAC A/C tables. by the way I'm using a tune from Brian.

 

My car kinda does the same thing. It's a 92 with A4 and as soon as I put it in gear, it will try to die. If I give it a little gas and then let it settle back down, it is fine. It's as if the IAC won't respond quick enough. I have my warm idle IAC counts down to 20, but when I put it in gear cold, the counts shoot up close to 160. What are your warm idle counts? Are your counts going to max when you put the AC on?

 

no...thats whats strange about my problem:

idle, a/c on, open loop = 109 +/- 10 counts (rough unstable idle 400-500 rpm range)

idle, a/c on, closed loop = 75 +/- 10 counts (good idle around 950 rpm)

idle, a/c off, closed loop = 35 counts (good idle around 950 rpm)

 

99, since I know little about your car, I will just throw this out. Maybe it is as simple as your tuning in Open loop. I don't play with LT1 edit so I can't comment on the tables. Good luck!

 

You might want to send bryan a datalog or something then.. Setting IAC counts is everything.. especially if you've severely cut the effecentcy of the motor OR if your turning something big like a T-trim in my case.

 

Well today I finally got the opportunity to work on my own car for a while and I was able to resolve this little quirk.

I was a little discouraged about having to raise my IAC counts so high, it seemed like everybody else had to. In the back of my mind it was nagging me that it had something to do with my Holley TB but I couldn't remember exactly what the catch was. I seemed to remember that there was something about the TPS but I couldn't remember all the details.

This morning I decided that I was going to fix it once and for all so I headed down to the garage with my laptop, and shop manuals. The first thing I did was look up the self zero range of the TPS, between .3 and .9 volts. I then connected everything and found that as it sat my throttle body was at the very bottom of this range. I thought I would adjust the throttle stop screw until I could split the difference. I started turning it and VERY quickly I ran out of adjustment. Hmm... I only manged to get the TPS up to about .4 volts. I cycled it a few times and let it slam home and it settled at .35. Not exactly the kind of adjustment range I was hoping to have but I thought I would try it anyway.

I started the car up and it settled perfectly into a stable idle. I turned on the A/C and it didn't act like it wanted to die at all. I just watched the IAC counts rise and of course you could hear and feel the extra load, but it handled it perfectly. I cycled the A/C a few times and it never acted up. I left the A/C on shut the car off. I started it back and it behaved perfectly. I then took the car for a drive and got it up to full operating temperature. I fiddled with the A/C several times and I couldn't make the engine hiccup at all. Again I left the A/C on and shut the car off. I allowed it to heat soak for a few minutes and then started it again. The car behaved perfectly.

Ultimately I think I could have got the same results by raising the IAC counts yet higher in the computer but they are pretty high already. By adjusting the throttle body itself I was able to buy the IAC more headroom with which to play with and it really seems to work well. Little quirks like this really make me wonder again why I spent the money on the Holley TB, but it's resolved now.

Thanks all for your help, especially Alvin for talking with me in more detail about it on the PM. I'm convinced the forum can fix anything eventually with the correct input.

 

I fixed my ilde hunt the same way but it is causing me spilt BLM's at idle. I am planing on trying to close the TB down a bit and let the IAC counts rise and see if that fixes the BLM split, It is my understanding the more air you can force through the IAC passage the less turbulance the bigger cams like mine will distrupt the air and there for stop the split BLM problem. I know the BBK TB's need to be mdified because they have passages the holley and stock TB don't allowing air straight into the intake the same as the TB does, but I have the holley so I am hoping with a little tweaking I can have cold A/C a proper idle and no split BLM problem, wish me luck

 

Well I'm good with cold A/C and proper idle. I gave up on the split BLM thing a long time ago.

 

Drilling a hole to bypass the IAC can help this too. I ended up drilling a hole, pitting in a piece of 1/2" pipe to close the passages FD2BLK is talking about, and cracking the TB blades a bit. Idles like a champ now with IAC counts in the 20s (no A/C). Without drilling the hole I had issues with the car stalling after stopping.

 

Early Holley TB's had an issue with incorrect IAC passages. The new ones have corrected the problem.

 

Nathan, What was the problem and the fix??? I think I probably have an early one, got an e-bay special. I had to pull of the linkage and tack weld my stock TB linkage to get the thing to go to WOT but that was abouut it then all was fine, oh exept adjusting the TPS to .47 VDC.

 

Through a suggestion of STL94LT1 I raised my "closed" IAC (sorry I don't have the exact table name in front of me) timing by about 4 degress and that seemed to fix this same problem for me.

 

RUKWKR, was it the "Closed TPS spark advance -vs- RPM"? How did it respond, and where are you at now?

 

The early Holley TB's had the IAC passage that just vented to behind the throttle blades instead of forcing it through the IAC passages in the intake. Reaming the hole slightly larger and installing a piece of copper or brass pipe would effectively block the passages to the intake and force all the IAC air to go through the idle circuit in the intake.

 

This is a problem on BBK's as well.

 

Yep, that's the one. I added 4 degress from 0 - 1200 over stock - I don't have the table in front of me because I'm on the road - and it seemed to not only help idle speed but also the quality of the idle.