When I have the car in Park IAC counts are around 40 and the idle is pretty smooth. When I put the car in Drive IAC counts will jump almost up to 80. From what I understand high IAC counts indicate the PCM seeing more fuel therefore it requests more air. Any ideas to why this is happening?

 

Idle air is adjusted to keep the idle speed at the RPM programmed in the PCM. It is not responding to "fuel" demand. It responds only to RPM.

 

To add to that, I believe that the idle RPM's are set higher to keep the car 'ready' to rock when it is in drive. In other words, that's so you dont stall when you gun it from a stop. This is completely normal.

 

uhhhh.... no.

Target idle speed for the A4 is 650rpm in neutral and 550rpm in drive.

When you put the tranny in drive, there is more load for the engine to overcome, so its going to need more air. So it would be normal for the IAC to increase... but I don't have an A4 so I have no idea what sort of values are "normal".

 

Well I am trying to work around a problem right now where my MAF is seeing 13 g/s at 850 rpm idle which it is set at in my tune. The IAC counts seem to correspond correctly with the MAF readings. My idle is pretty rich and I keep getting the occasional KR while driving. Thing is that it is something that is constant...one day everything will be fine and the next everything will be off.

 

So you're saying that the IAC counts go up when you shift to drive, but the RPM setpoint goes down? I wasn't aware the increased engine load could demand that much more air. But I don't really know, as I don't have an auto, either.

With respect to the rich condition, is the PCM entering closed loop operation? If so, and everything is working correctly, it should trim it back to a good A/F ratio. You could also have a misfire that is giving your PCM a false lean, but is telling your nose that its rich.

 

Idle in park is 850. Idle in drive is 775. When I shift into Drive the IAC counts almost double. I am not throwing any codes and I have had misfires before and this doesnt feel like a misfire. Really the only thing it feels like is the computer pulling timing. Some days it will act like this and some days it will be perfectly fine. I have replaced nearly every sensor on the car in the past month with only mildly successful results. When I replaced the IAC it ran better than ever for a week and then just all of the sudden jumped into the slump again.

Any more ideas?

 

Just a suggestion.... when you post a question like this, include all the info "up front".... like the fact that you are running a custom tune, and I suspect (but don't know, since you haven't told us anything) something other than a stock engine.

Wastes everybody's time when you don't include all the info.

 

Sorry Fred.

LT4 hotcam
PCMforless tune
MAC headers
stock heads
misc other bolt ons

 

what all have you done as far as troubleshooting goes?

 

Try unpluging the MAF and see what it does. Because I know it will run in open loop mode. Which wont pay attention to some of the sensors readings. Which would help diag if its missfire or etc...

 

As far as troubleshooting goes I have done just about everything I can think of but I will list.

1. unplugged MAF...ran well for 1 day. Plugged MAF back in ran fine for another day...same cycle as I have tried this numerous times
2. tried different MAF
3. new IAC
4. new TPS
5. new O2 sensors
6. new IAT
7. checked injectors for leaks
8. replaced gaskets on headers b/c they were leaking at one time
9. adjusted rockers 3 different times
10. put stock airbox back on
11. resealed intake thinking i had a vacuum leak
12. cleaned TB

I changed out the MAF and IAC together and when I did that the car ran great for 1 week. Then I got in it one night and it started stumbling and giving a few degrees of KR at normal cruising. That has been about a week ago and sometimes it will be completely fine and other times it will just feels like timing is being pulled. The running bad is accompanied by a pfft tick pfft tick sound if that helps any

Occasionally on startup the car will idle to around 3000 rpm and hang there for about 10 seconds before settling down.

 

The part that throws me off is when you said it will run fine for a day. Sounds almost like the pcm looses its memory? Dunno what else would cause it to just start acting up?

I wonder if you have a bad PCM. I saw a similar post on this forum about couple people getting bad pcm's. And having to send it back to pcmforless.

Dunno man. Sorry I cant help ya out.