Guys,

Last year I completed my engine rebuild with significant mods. Before I could get it tuned, I was laid off. I have been driving it with the stock tune and it has been running fine except the idle is very low in open loop. The problem seems to have gotten worse in the warm weather to the point where it stalls at traffic lights, expecially if the AC is on.

The IAC is at 160 at cold start up and comes down as the engine warms up (see second file to see it come down). I have opened the throttle stop screw some to try and raise the idle but it doesn't seem to affect the idle any more. It runs great otherwise. It also looks like I have split BLMs but not severe if I understand Datamaster correctly.

I see no signs of exhaust leaks or intake leaks. Do I need to just get a tune done or do you think there is a problem needing repair before I attempt the tune based on the attached uni files? The problem seems to have gotten worse in the warm weather but that could be a coincidence. I don't want to pay for a tune if there is an issue needing repair first.

The first file is with the engine almost cold and the second is after the engine is almost to full operating temp.

https://www.medialightbox.com/public...tzrag/3pzyug8w

Any guidance would be appreciated. I am relatively new to tuning but happen to be an electrical engineer with a degree in digital signal processing so I understand the principles of a control system. Just need some guidance how to interpret and what I should expect to see.

I would appreciate if any of you experienced Datamaster guys could take a look and point me in the right direction.

Thanks!

 

I haven't had a chance to look at the data logs, but you indicate the problem is low idle in open loop. Since the PCM should only stay in open loop about 3.5 minutes from startup, how does it run in closed loop? Does the problem go away?

 

Both files are for a fully warmed up engine.

The second file is only 79 frames of idle. It that what you intended? Its in closed loop, IAC is at 160, AC is on, and the idle drops to the 500's (against a target of 650 rpm, must be in neutral). In the first file, the problem seems to disappear when the AC shuts off. IAC counts drop from 160 to 94 (record #1057). Start your review at record #731, stepping forward one frame at a time, and watch AC Clutch and AC Request flags in the upper right hand corner of screen.

 

Fred,

Both of those files were sitting in the driveway. The car was sitting for about 2 hours before I created the first log. I thought it was cold but maybe not. The second file was created about 10 minutes later. I only ran the log for a short period because I didn't want to overload you with data.

The idle gets much better with the AC off although it seems a little low to me.

What conditions would make the best file to evaluate this idle problem? Should I drive it and how long of a file would be best to evaluate. I'll generate a new one tomorrow morning when I know it is cold and note the ambient temperature.

Anything else I should do to get meaninful data to show this issue?

Jeff

 

Its programmed to idle at 650 rpm, and its idling at 650 rpm or above in just aboout every frame, once the AC shuts off. Why do you feel its still idling slow? That's the stock programming for an A4 in neutral, fully warmed up. The cam doesn't sound very large, and MAP is good (48kPa) once the IAC closes down below 100.

When its idling low, its in drive and the AC is on (target idle is only 600 rpm). First appears you put it in neutral, and the target rpm went up to 650, and then you turned the A/C off and it dropped the IAC counts and its idling exactly the way its suppose to. It may not be smooth, because you haven't had it tuned.

You indicate that opening the throttle stop screw did not change anything. When the IAC counts are at 160 (in drive, AC on) the engine isn't getting enough air. At that point, when you open the blade stop up a little, first the rpm should start to come up, and when they reach 600, the IAC counts should start to drop. If you were opening up the throttle stop with it in neutral, and the AC off, its not going to increase the idle, because its already at the correct idle speed. The IAC counts will just start to drop.

In the second file (the short one) the idle is about 50 rpm too low, the IAC is maxed out, its in neutral, but the A/C is on.

Have you ever cleaned the IAC motor pintle, and checked to make sure the IAC passage isn't dirty?

 

Fred,

In the last month or so, when the AC is on, if you put it into drive, the car will stall. I rebuilt the engine about 2 years ago and everything is virtually new. As I mentioned, it is still on stock tune but idled fine until this summer. I have been suspecting the extreme heat and maybe the need for a tune but wanted to rule out a mechanical problem before I spend the money. I was going to have Bryan from PCMforLess dyno tune it. I live not too far from him.

As you suggest, I am going to check the IAC pintle and passage this morning to make sure it is clean and then do another test run on DataMaster to give you a better picture. I will start from a cold engine. I'll post the uni file later today.

Thanks for your help.

Jeff

 

I did another test run this morning for about 20 minutes. The car did stall about half way in. I also noticed I had 2 trouble codes set (37 & 48 - stuck brake and MALF malfunction). I replaced the ignition switch a few days ago so I believe the stuck brake switch code is from that.

I can't explain the MALF code. Do you see anything in this new data file consistent with a MALF problem. By the way, the ambient temperature when I first started the car was 80 degrees. Does DataMaster show the status of the trouble codes in real time on playback? I am wondering if the code set during the stall and is not real. On playback it appears set from the beginning which I don't believe.

https://www.medialightbox.com/public...tzrag/2fyy94i9

Thanks again for your help...

Jeff

 

Use Shoebox's LT1 code list. DTC 48 is for failure of the MAF sensor.

http://shbox.com/1/Dtcs.htm

I don't think DataMaster shows when the code tripped. It just shows that it set sometime during the run. I wouldn't write off the codes as due to the stall. Maybe the stall was due to the MAF code.

 

Random thought... what brand is your 52mm throttle body? Have you ever inspected the idle air passage for casting flash?

 

It is an Edelbrock. I got the whistling sound when I installed it and I sanded the edges of the idle air passage. It got better but still whistles some. That was a year and half ago but I inspected at the time and didn't see any casting flash. I remember considering the drill mod but didn't do it.

I will reinspect for carbon, flash, etc. and let you know. My first 2 logs don't show the code 48 and I have never received a check engine light or cleared any codes recently so this appears to be the first time it occurred. I was surprised to see it on this run. That is why I thought it might be related to the stall. I cleared it so will see if it comes back.

Will try to inspect IAC on Sunday and post my results. Thanks guys for walking me through this.

Jeff

 

Don't want to jump in on something you guys are already looking at, however I took a quick look at July 17 .uni. In records 1 to 813 IAC is maxed out (open) at 160, rpm is 400 desired rpm is 900, AFGS is low, looks like this thing is not getting enough air through the IAC and TB blades. TBS voltage is .53 but are the blades opened a crack (enough) to help the idle and the TPS adjusted for that. Earlier post said opening blades did not effect IAC counts, if not something is messed. Open blades should increase idle and PCM should lower IAC counts. Are you sure opening the blades did not effect IAC counts..

 

What he said in the original post was that opening up the blades did not increase the RPM. I tried to explain why that was happening:

 

The car sprung an antifreeze leak yesterday so I haven't had a chance to follow up on this. Had to let the car cool overnight so I could work on it tonight.

It was a more than a year ago that I originally opened the blades a little when I first did the rebuild it did help at that time. But when the weather started warming this year and I started to notice the low idle, I tried opening them more and did not see any change.

I am going to inspect/clean the IAC port as Fred suggested and readjust the blades to see if I can get the IAC count down and maintain the correct TPS voltage.

I'll post probably Thursday night. Thanks for all your help.

 

While checking for that coolant leak and trying to keep the car idling, I moved the butterfly valve and noticed a little sticking off idle. So I cleaned the bore and blades and sprayed some carb cleaner inside the IAC port as Fred suggested.

It made a huge difference. Now the car is high idling when first started and I can hear the compensation when the compressor clutch engages. I think we have this solved. I am running a bottle of Sea Foam through the gas tank and will introduce some through the vaccum port on the driver side to clean the inside of the manifold.

I never had to clean the throttle body or manifold when the car was stock and when I rebuilt the engine at 323,000 miles, the manifold was remarkably clean. The rebuilt engine has about 75,000 miles on it. I am wondering why it seems to be suffering from more carbon build up now. Could it be because I have not yet had a tune done? What else could cause carbon in the intake plenum/throttle body before the combustion chamber?

 

Minor point.... but I wouldn't have told you to use "carb cleaner" in your throttle body. Its too harsh and may remove the anti-coking coating on the blades. You should always use "throttle body" cleaner on a throttle body.