Sitting with the car warmed up (have a fan switch, right now with the fans on low it sits at ~195 at idle) I noticed some knock retard when I rev (up to 6 degrees especially when I rev, let it come down then rev again), only right off idle almost like it is bogging(hit the gas again and it doesnt want to go for a second). Someimtes it does it, sometimes it doesnt. Just had plugs, wires, opti, fuel filter done. I am doing the coil (current one is a hypertech with about 55,000 miles on it) this sunday and I just ordered throttle body gaskets and a new IAC just in case mine is too dirty to clean. Right now my idle is right at 800, sometimes goes up to 825-850, but it is rougher than it was before. Could a dirty IAC and/or bad/failing coil cause me the knock retard right off idle? The car runs really well through the powerband all the way the my mental redline (5600 RPMs on factory tach) but it runs weird right off idle, sometimes I have to play with the clutch to make things smooth.

 

How old are the O2 sensors? They can cause some screwed up issues. Best way to diagnose this would be to find someone with autotap or similar software.

 

I am using the original O2 sensors, car has 97k miles currently. I have a scanner and tehy seem to be within normal range (jumping from 100-800 or so but always within about 50 of each other in the same data cell). One thing I did notice on a scan is that when I did a WOT run and slowed down in gear the O2s went very low, like 5-10 for about 10 seconds then when I hit idle they went back to normal operation. Does that sound like normal O2 operation?

 

At WOT the computer doesnt take readings from the O2 sensors. Still 97k on the original sensors is pretty high. You might have a bad plug or a burnt wire. That would cause a pretty rough idle but it would also make the car run pretty bad as well. I still say you need to get a data log for your car...that will allow you to see all your sensors in relation to each other. You can usually find the problem easier that way.

 

Your O2 readings are normal. They should cycle form around 100-800 at idle, and when you decel your computer cuts out the injectors so you should read a really lean mixture <100... so your readings as far as that goes seem right on.

You could have just gotten some bad gas. Or your could be reading some noisiness in your drivetrain. A good recommendation to discern wether you're getting knock retard or not is to put some really good gas in the car and see if it goes away. The LT4 knock module is also a pretty cheap upgrade that many people use.

Jonota

 

Couple of notes, sorry need to update cig:

EDIT: I also put two cans of 104 octane booster in about 8 gallons of gas and still had the same amount of knock, but it never is over 6 or 7 degrees and it is highest when the car is a little out of control (spinning tires, hard shift that rocks the rear end, etc.)

Have the LT4KM, reduce my knock almost entirely. I noticed that I have almost no knock if the tires are not spinning and the shift into second is nice and smooth and the tires grip, if I break them loose a little into second then I get more knock

As far as plugs and wires I had them done within a month along with the opti and fuel filter. Also my injectors were taken off and cleaner.....when i go the car back it was a night and day difference, was WAY overdue for those things.

Cleaning the TB and doing a new IAC next weekend. If that all doesnt clear it up I have an MSD coil waiting to be installed.


What about EGR, if it was clogged or something would it cause the off idle problem? I have never cleaned it or anything, would taking off the manifold to intake hose and cleaning it and replacing the gaskets help? Or even replacing the valve/solenoid?


THanks for the replies guys, trying to make my car run right so I can convince my fiance to keep this money pit

BTW PM me if you like bootleg movies lol

 

it would be helpful if you could tell if it was spark retard or knock retard. Ie, what are your knock counts doing when this happens? One thing that seems to be a problem is knock retard right after a shift. I am currently having this problem as well. I have some suggestions to cut it out of the programming in the car, but need more info on it. Is this the only time you are getting it??? Also, listen to see if you just have a noisy valvetrain (lifter, loose rockers, etc)

Jonota

 

My vavlvetrain is noisy, but no noisier than when I got the car 70k miles ago. Ticking sort of, nothing out of sync or aynthing. I get retard before the shift as well but it is less when the car is under control (I lose a little traction at higher RPMs if I started out a little off in the lower RPMs)

Right after the shift I do not see a huge jump but I think I need to get a ALDL laptop cable to see split second readings to diagnose this

 

probably best to do that. you might actually be leaning out too much on top. if you had access to the program you could fatten it up or bring down the advance a little.

jonota

 

What about the EGR system? If it is not too hard to change out I would like to clean the tube or replace it and reaplce the valve/solenoid. Since I plan on keeping the car forever and I dont want to remove the EGR yet should I just go ahead and do it myself or is it a mechanic only thing? (I can do anything besides internal engine work I guess, have people helping me too )

 

You can clean/change out/block off the system or whatever it is you want to do, the whole system is very simple. i doubt it has anything to do with your system. You can do the EGR test. Run at idle, then apply vacuum to the diaphragm and see if the engine stumbles/stall. That will tell you if it is stuck open or not.

Other than that I believe you would get an SES light if it engaged in the upper rpms.

jonota

 

Damn I owe u one. Thanks, tried that and my EGR is OK.

Now, for my IAC, I have a 1995 M6, do i have a KC4 engine oil cooler? hehe, ordered the one for 1995+ without it doh

 

Have you checked to see if you have a vacuum leak? This could be causing your funny idle, your bogging, and your retard problem. If you don't know how to check, get some carb cleaner and spray it around in the engine bay with the engine running AWAY from the air intake. If you idle changes sounds then you probably have a vacuum leak.

Jonota