I'm attempting to tune my 383 tpi with maf using the Moates AutoProm. I have the edelbrock long tube runner setup with 58mm throttle body, #24 injectors, mild cam .444 int/exh and factory cast iron heads. The engine has a very unstable idle fluctuating between 800 and 1100 rpm. At this point I have replaced the IAC and reset the TPS. I have checked for vacuum leaks and haven't been able to find any. The idle problem still exists and I'm starting to wonder if my ECM is bad... I noticed that on the data-log of the engine sitting at idle the "target air fuel ratio" (not the actual afr) has huge spikes in it.. Shouldn't this be flat lined at 14.7?

 

What changes to the timing table and desired idle rpm tables have you made?

Also are you positive there are no vacuum leaks?

 

I am using the APYP BIN, the Spark table starts at 20. when I increase the timing the idle becomes even more unstable.. I have also tried using the Spark table from an 89 350 tpi camaro and it starts out lower at 17.93, this causes my engine to stall unless my foot is on the gas.

So far the best idle setting is at 800 rpm but it still fluctuates up to 1100. When I raise the idle to 900 it fluctuates up to 1200 or 1300 rpm. If I take the idle down to 700 rpm the engine wants to stall.

I checked for vacuum leaks by spraying carb cleaner around the intake, runners and throttle body and listening for an increase in rpm. Do you have a better method to check for vacuum leaks?

 

Starter fluid is sometimes used around intake but just be careful

How much duration on the cam? What you can try is lock out the timing aroun the idle cells. Target 800-850 if somewhat medium large cam. Log the car at idle and see what lv8 values you are hitting. Bigger cams need more timing than stock cams. Depending on size it may need 25-30 deg just at idle. After you see what the idle lv8 is, go to timin table and lock all cells around that idle rpm and lv8 value at the same value. This will prevent timing from fluctuating and in return, help keep rpms stable.

Next step is to work fueling. Maf table 1 for this and monitor o2 sensor data, blms if trying closed loop. Wideband can help some here. Find the fueling it wants. Can read plugs to see mixture, you want light tan at idle. Not to white or to dark. Also can monitor idle vacuum. The closer you are to ideal idle air fuel and timing, generally see most vacuum

 

My cam duration is 212 intake and 218 exhaust with lobe separation of 114. I was told it was a computer friendly cam when I bought it.
This is great information, I will give this a try tomorrow and let you know how it goes.

 

That cam shouldnt have much issue at all. But never know with these cars. Keep playing with it.

 

Before you get to frustraighted,try and set your base idle which will effect IAC counts.

 

I tried what you recommended and it didn't make any difference so I decided to peek around the engine a little. When I pulled the valve covers I found a rocker arm laying there along with a broken stud from the head. I took a compression check on each of the cylinders and found that two of the cylinders had no compression. This would explain my terrible idle problem along with lack of power. The car is now fixed, it idles smooth and runs pretty well. One problem is that when I am coming to a stop the motor wants to die. The rpms drop to 450 for a brief moment then it catches itself and increases back to 850 rpm. On my data log it shows the engine going rich when it fights to keep an idle.

How can I fix that problem? I see Decel Enleanment in the scalars but I'm not sure if I should mess with it.

 

Can play with maf table 1 at low grams/sec flow as well as stall savers. Adjust the rpms and spark advance there. Generally i raise them up the same difference as your new cam idle speed minus stock idle speed, give or take. Stall saver rpms usually are hundred to 200 rpm below actual idle

 

This is almost identical to the issue I am having...same engine, same ECM, same injectors...Cam is 218/224. Thanks for the ideas!

 

As mentioned earlier above, after you burn chip with desired idle speed, you need to set min idle speed via the throttle body screw and reset iac

 

Did you replace the intake base? If so you could've slipped an intake gasket and could be sucking from the crankcase. I've seen this many time before.

There are two ways to check this. The first...

Remove BOTH crankcase breather while the engine is running. Then put your thumb on both or if you don't have monkey arms like me, have a buddy plug one while you do the other. You'll feel your thumb suck in.

The second...

Pull the plugs, one will be oil soaked.

 

I adjusted the stall savers to 700 and played around with the maf 1 table as you suggested but I don't see any improvement. Whats happening is that when I start the car it idles fine then when I rev the motor to anything over 2000 rpm and let off the engine stalls. The same thing happens when I am cruising and I am coming up to a red light, I push in the clutch and the rpms drop so low that the car stalls. It doesn't happen all of the time but quite often. My data log shows the rpms dropping as low as 275. Is there something else I can adjust?

 

Likely need to disable the stall saver. The reason is that it reverts back to the base timing, which on modified engines causes it to stall. I have a write up on this someplace, let me find it and I'll post a link.

RBob.

 

Ignore the title, more info inside the thread:

https://www.thirdgen.org/forums/diy-...ver-sa-8d.html

RBob.