Fred, Sorry for dragging out this old thread but it relates to my current problem. Now that cold weather has set in here in sunny NJ, my IAC count is pinned at 160 until the engine starts to warm up and then it comes down to normal range. I have not done a drill mode or adjusted the throttle stop yet.

My question is, if I adjust the throttle stop as you mention in this thread to give my IAC servo more head room so the high idle works on cold starts, should I do it when the engine is cold and in high idle mode? It seems this would be when I could tell if the IAC is no longer pinned at 160, but then how will I know what RPM to adjust to since it is in high idle mode? Once the car is warmed up, the IAC count is normal and the idle RPM is normal so it doesn't seem correct to make this adjustment after the engine has reached normal operating temperature.

Can you clarify this for me? This is my first winter since installing my mods so I am just now running into this for the first time.

Jeff

 

Are you sure the IAC motor is actually moving? Is it possible the IAC passages are dirty? The scanner indicates that the PCM is trying to open it, but if it isn't actually opening (or the air flow through the passage isn't increasing), the PCM will just keep increasing the counts until it max's out at 160.

 

Yes, it is moving. I tested it also using Shoebox's procedure and it tested OK. Because it was about the only part I didn't replace during my rebuild, I replaced it anyway. I get the same behavior with the old and new IAC valve. I have a new Edelbrock 52mm throttlebody and the IAC port is clean. Once the car warms up after 2 or 3 minutes, the IAC count comes down and the idle starts to respond as the IAC drops below 160 so I believe the IAC is moving. The car just won't high idle when it is cold and the IAC is pinned at 160. Since this is the first time the car has seen cold weather since I installed all of my mods (cam, throttle body, etc.), I think I just need to either adjust the throttle plate stop screw (and maybe TPS sensor) or drill the bleed hole.

I wanted to get you opinion before proceeding and get clarification on how to adjust the stop screw.

Does this sound like a throttle plate stop screw adjustment issue or a bleed hole drill mod to you?

 

First, I'd try pushing out the throttle stop screw to provide more air. If that doesn't work, then try the drill mod. Be sure to check your TPS closed throttle voltage to make sure it doesn't go too high when you open up the blades.

 

Thanks Fred,

My idle speed is perfect when the car is warmed up and during the warm months. Will this adjustment allow the high idle to work without sacrificing the normal idle speed? I guess what I am asking is as I open up the throttle plates, will the IAC compensate and keep the idle steady at normal operating temp? Is the idea to give more headroom for the high idle on cold starts without affecting the normal idle speed?

I'll test it and see. Just trying to better understand what to expect.


Jeff

 

Fred,
I just tried adjusting the throttle plate stop screw. It seems to have helped. The car now high idles around 900 - 1000 RPMs on cold start (it is around 32 degrees out). I turned the stop screw out about 3/4 turn. The TPS voltage went up to 0.53V so I adjusted it back down to 0.49V.

The IAC is still pinned at 160 until it warms up but I am getting some high idle where I wasn't before and it comes down faster. When the car warmed up, the IAC count dropped down to about 16 at 650RPM.

When I turn the AC compressor on, it cycles between about 12 and 32 although one time it dropped to 8 and the car stumbled a little bit.

It seems to be running OK now but I'll have to wait until tomorrow morning to test for a real cold start again.

Do these numbers look like you would expect for my setup or is the IAC count too low (16)? I am not sure how I can eliminate the 160 max out completely and keep the bottom end up. It may be OK where it is.

 

The TPS voltage just has to be between 0.20-0.90V.

Stock programming for an A4 at 32*F would be 950-1000rpm.

Seems a shade low, but if it keeps the engine at the programmed idle speed, it should be OK.

I'm trying to think of why its having such a hard time keeping the engine at high idle when its cold, but not having a problem keeping it idling when its warmed up.

 

Interesting info about the RPM at 32 degrees. Do you have a whole table that I can compare against? I still have factory programming at this point.

This morning, it did idle about 950 RPM and it was 37 degrees which seems normal, but the IAC was at 160. When it reached normal operating temperature, the idle was at 650 and the IAC dropped to about 21-22 which I know is at the low end of the normal range of 20 - 40.

My concern now is what will happen when the outside temp hits 10 or 20 degrees? Will the IAC be able to reach the desired RPM for that ambient temperature? I don't want to open the throttle plates any more because then it may idle too high when it is warm, right?

 

The stock idle vs. temp settings are in my online scanner writeup:

http://members.aol.com/InjuneerZZ/ScanMast.htm

Don't get hung up on "20" being the minimum "normal" IAC counts. I suspect the "20-40" comes out of my scanner writeup, which is just my ESTIMATE of what you should see, based on what I saw on my car and on scan logs from a bunch of other cars.