I am trying to smooth out my idle.... I am running the LT4 Hot Cam and it idles well but the engine shakes. At a timing setting of 25 degress at idle it will register spark knock. I zeroed out the idle advance/retard timming correction tables since I was seeing the idle timing go up to 29 at times and it didnt help too much but some knock was removed. I then set the idle timing to 20 degress in the chip and almost all the knock is gone The car shakes like its missing and I think it may be a lean miss at idle? It shakes like this at any timing between 20-25 degrees and the BLM at idle is 128. The dizzy is set at 8 degrees.
The exhaust stinks, I am not running a cat, but it doesnt smell rich...just an odd smell. My cloths/hair smell real bad after just walking behind the car. Another thing that has me thinking its lean at idle is when I first start it and its in open loop and is being richen up by the open loop tables, the engine doesnt shake nearly as much. The hotter the motor gets the more it shakes/misses.
Has anyone else smoothed out the idle by riching up the O2 constants? Is the general consenses that when you swap a cam with a bit more duration 218/228 degrees that the car will smooth out with a bit richer idle. What method is used? What increment did you start with, 50mv?? Anyone with a hot cam have any success with this?

 

I have an old school 1960s 327 with a choppy hydraulic cam, something around 310 adv. duration, and I can get a good constant, non-hunting idle warmed up using a 1989 Corvette bin, with a timing map that I did myself. I'm sure that the "hot cams" that you guys run with roller setups don't idle anywhere near like this does -- this has the long overlap muscle car choppy idle to it. I'll send you my bin if you want to take a look at what I did. The only issue I have is that the IAC is acting as a follower coming back down to idle from extended driving, and the idle takes a little while to come back down to target. The throttle response at all rpm and load ranges is amazing though. I did play with the O2 error reduction tables, because I'm running a 4 wire heated Delco O2 sensor (in one long tube header only). I'll have to see where my BLM's are idling when I get my datalog back up tomorrow, but changing by 100 millivolts still didn't make any noticeable change to the car's running or exhaust (this car always has a very very rich exhaust smell, even when it was carbed, just due to the cam overlap. I was trying to see if I could skew this a little to lean it out, but it looks like I can't really, without changing the MAF tables at low flow. The car drives so well and throttle response is so good that I'm not going to mess with the idle too much.

 

So riching/leaning out the idle wont help any with smoothing it out some and help with the smell?

 

A smoother idling cam may be affected a lot differently than my setup -- I'm pumping a lot of inert gas past the O2 sensor because of my long cam overlap.

 

I wouldnt pay much attention to knock at idle. It could be due to any number of things. It sounds alot like what I ran into in the past. Engine misfires and the exaust has an odd, penitrating smell (well, it always smells, but not that bad). I was really lean. Id try adding more fuel, like a 10% increase, to see what happens. If it runs better, then you know youve just got a lean miss with incompete combustion. Also, adding more O2 bias around where the car idles can help. Itll cause the ecm to target higher values and increase the BLMs to add fuel accordingly.

 

I had my best result son my hotcammed 350 with the following:

Minimize the IAC influnece get it down to single digits or even 0 at idle so u have no IAC counts when hot in gear.

Played with timing from 25-30 degrees at idle, ended up best with 28 degree in the main tables and limiting the advance/retard correction tables to 2-3 degrees to allow a slight variance/adjustment. (Seemed to be better off having some correction, because the idle would dip occasionally no matter what).

I never had the chance to play with the 02 constants in a good clean fashion and get some real test results with it. However, they can defintiely influence the smell of the exhaust and how your car idles. I made it that far, just never had the car working right again to verify what results i actually experienced.

later
Jeremy

 

It just seems odd that I am getting hundreds of knock counts at idle??? And the engine just kinda shakes like its missing...but give it some rpms and she smooths out.... I am gonna try fattening up the idle tonight and if it improves I am gonna slowly add some timing back into it to see if that helps too. If its better ill add some SA idle control back to the ecm.
Also I hear about a mod to allow the car to idle in a different BLM cell...what would that do???
Thanks!!