Very rough idle

[MCHdrivesan86GN]

My car has been running fine and last night I opened it up a few times just playing around. The last time that I went to tip in the throttle, I got some response out the car and then the scanmaster showed 13.8 degrees of spark retard. I then pulled off the interstate and came to a stop and the car had a very rough idle and I had to give it gas to keep it from stalling. It was almost like it was missing on a cylinder or two. I managed to make it home and took a look and a listen with the hood up. I couldn't really see anything or hear anything, other than it appears that it is only firing on 4 or 5 cylinders and sometimes when it would stall it would sound as if something was depressurizing.

There were no error codes or service engine soon light.

So given that I seen that amount of spark retard and fact that it appears that one or more of the cylinders did appear to be firing I did a compression test and all 6 were about 150psi. I checked all the spark plugs and they seemed to be ok, however, I didn't check to see if each were firing. I did get a data trace and the only thing I see out of whack is IAC, based off Quick Reference.

This post should have probably been posted under driveability/troubleshooting, although my original thought was I had popped another head gasket but the compression test ruled that out, I think. One other thing, my fuel rail pressure is good. This is one of the first things that I checked and the fact the car seems to be okay when driving it.

I don't know if anyone has any advice and next place to look. I have an excel file attached with the 20 or so seconds of data. For some reason, .xls is an invalid file format so I zipped it up and attached it.

Thanks.

[kenmosher]

What tool was used for the data trace? Was it hooked up when the car had the problem? If it's a DirectScan or PowerLogger, check the connector to the ECM ... if they move around or lose connection, the ECM will wig out.

[Keller]

Originally Posted by MCHdrivesan86GN

For some reason, .xls is an invalid file format so I zipped it up and attached it.

I can add it to the file formats. Given the current popular scan tools, picture formats, etc. it just hasn't been necessary. The less attachment types available for posting, the less potential issues we open ourselves up to.

[MCHdrivesan86GN]

"What tool was used for the data trace? Was it hooked up when the car had the problem? If it's a DirectScan or PowerLogger, check the connector to the ECM ... if they move around or lose connection, the ECM will wig out."

It's the free windows based scan tool, WinALDL, and initially it wasn't hooked when the problem surfaced and the problem is there with or without my laptop hooked up.

"I can add it to the file formats. Given the current popular scan tools, picture formats, etc. it just hasn't been necessary. The less attachment types available for posting, the less potential issues we open ourselves up to."

Less is better, I agree. No need to add Excel file format on my behalf. I can figured how to get data into a supported file format.

If there is any information that I can provide or suggestions that anyone has for me to try, I can provide and I'm all ears.

Thanks.

[Keller]

The Excel format is fine. However, with so little data, it is very hard to see much.

Your BLM is 147 at idle. That is high, and means you are LEAN. See http://www.gnttype.org/maint/quickref.html and connected links.

You likely have an air leak somewhere. And your TPS looks to be out of adjustment. Possibly high, but I'm not sure I am reading it correctly. It appears the reading is 0.6V.

[MCHdrivesan86GN]

I get can more data. The data that I took was from a start, until the car stalled. I would have to give it a little gas to keep it running. I also make a visual note of the tps.

It also sounds like I have an air leak. Bare in mind, my car was running fine and it appeared that there was some detonations and after that...

Thanks.

[MCHdrivesan86GN]

Here are a couple more data traces.

Trace1 - setting in my driveway giving it a little gas trying to keep it running
Trace2 - backing out and driving
Trace3 - driving
Trace4 - "idling" in my driveway

Keller, unfortunately WINALDL gives raw data or the data converted to engineering units. Does not explicitly give the sensor voltages, just the A2D counts in the data files. As far as the tps, I believe you are taking the raw A2D counts and converting to volts and that is simply 5/256*N. Which I checked at idle and it was 23 counts or ~ 0.44v so I think it's on the low end. I get a slightly different reading with the Scanmaster 0.46v, but close enough.

Anyway, I have not looked at the data myself I quickly formatted it (WinALDL dumps it into a text file, which is essentially unreadable) so I could get it put up here. If you view it, it might be easier to freeze the row 1 panes as opposed to column A when scolling down for the longer data files.

Once I start driving, car runs ok until I stop and let it idle.

Any help, is greatly appreciated. I'll be able to spend more time this weekend with it and hopefully figure out what is going on. I suspect something popped and air is escaping, but I can't localize it.
Thanks

[kenmosher]

It sure sounds like it has an air leak ... check:

1. All hose connections between the throttle body and the turbo. Especially the back of hte intercooler hoses, since they tend to "wiggle" off and LOOK like they are connected, but are leaking like crazy.
2. Check the vacuum hose block on top of the throttle body
3. Check the MAF hose for holes between the MAF and the turbo
4. Check the EGR ... does it change the idle if you move the diaphragm by hand (it's really HOT if the car has been running, so use gloves).

[MCHdrivesan86GN]

Given that I have blown a head gasket in the past and it appeared that there was detonation, I was inclined to believe the worst and I thought for sure I popped a head gasket. Compression tests indicated otherwise, but being inexperienced as I am I was sure I did something worse than pop a hose lose and didn't bother to check them, other than to do a quick visual inspection. Hopefully it is just a lose hose.

[Ts86ttype]

Do Kens' check list... It really sounds like a EGR stuck open... Tom G.