Rough Idle...

[Baldeagle242]

Hello All

Some of you may remember me from last year with the 1997 Malibu 3100 to 3400 swap. (see link for more info about my setup)
http://60degreev6.com/forum/showthread.php?t=37569

First off the car still runs and drives great has lots of power and is a lot of fun to drive. The only issue I have with this car is a rough idle. It is not to the point where the car dies and the RPMS are always steady at around 650+/-. The 3400 is a stock 2005 motor but the best way I can describe the way it idles is that it feels/sounds like it has a huge cam in it. Everything else is still stock on the car including exhaust, intake, etc...)

I still have all electrical parts and crap from the 3100.
HERE IS WHAT I HAVE TRIED SO FAR:
1. New Plugs (NOT the old 3100 plugs)
2. Changed the coils and wires (the old ones from the 3100)
3. Checked for vacuum leaks and can not find any.
4. This 3400 has the 3100 fuel injectors in it. (I have no way to tune the stock 1997 - 3100 computer for the larger 3400 injectors.)
5. I DO get a code that tells me I have a misfire on cylinder 2 about every 100 to 150 miles that goes away on its own after a day or two.
6. I have sprayed the entire electrical system down with water to try and find a bad wire, connector or short and this makes no difference at all. (Weather conditions do NOT seem to matter either.)

This seems to be SLIGHTLY worse when the motor is warm or after driving it hard. I have a few thoughts but lets see where this gets me...


Any replies welcome... Thanks in advance.

Steve

[Azrael]

If your EGR is stuck open it can cause a bad, lopey idle and hesitation while accelerating at low throttle. Usually associated with a low vacuum reading. ~-10 in/hg @ idle instead of the usual -18 to -20 when I had a similar idle problem.

[Baldeagle242]

This sounds like a very good possibility. I have not had a chance to pull the EGR but I did check the vacuum and it is at 16 in/hg @ idle.(650-700 RPM)
If I unplug the EGR will that tell me anything? -or- is there a go way to check the EGR?
I do not get any codes for the EGR. The only code I have ever seen on this car is missfire on cyl. #2.

[Azrael]

I found out it was my EGR when I unplugged it and the problem went away a day or two later until I drove with it plugged back in. I can only assume the valve stuck open until engine vacuum eventually pulled it back shut. I did this twice just to make sure. I have an older, Digital EGR that uses simple solenoids though and I'm not sure what I did will work on the Linear EGRs used on 96+ models.

[Baldeagle242]

I will unplug it before I head out to work and see what happens.

[Baldeagle242]

Well unplugging the EGR did nothing but turn the Check engine light on. I have since blocked off the EGR valve with a piece of tin between the EGR and the intake and that did nothing but turn the check engine light on for insufficient flow.
I still have a rough idle but the car runs fine once the RPM's are over 1000+/-. I think it is safe to say that the EGR valve is not the problem. I have put over 2500 miles on the car with the EGR blocked off. I think the problem may be the smaller 3100 injectors in the 3400 motor but I have not heard others talk about this issue. I don't think it is a leaking injector because I still average around 21 MPG but I know that the motor these injectors came from was hot enough to melt the underside of the heads.
This is a minor issue for me but it gets old having to explain to anyone that rides in the car whey it jerks and runs so rough when I stop.
Anyone have any other thoughts?