1986 camaro 355 with hsr, comp cam xfi 224/231 113 lsa and .488 lift, ported gm heads, 24lb injectors. Did the motor over a year ago and havent hardly put 200 miles on it because of this idling problem. I had the car tuned at a dyno shop with open headers he said may need touch up tune after exhaust got the exhaust put on all was normal for a day now the car will not idle have to feather gas to get it started and keep you foot in it to keep it running when it does idle it surges from 450 to 800 rpm. i have set minimum air via haynes manual and tps voltage. and the kicker tried a new iac with the old one idles to low and with the new 1 no matter what i do i cant get the idle below 900 to 1000 as soon as you plug in the new iac it goes into a high idle. Took it back to dyno he had it forever and claims its not a tuning issue... it runns smoothly throughout rpm range just wont idle...im at a loss for what to do also has new maf and relays, dist and coil and wires. There is a cel that comes on but no codes come up after jumping the diag term besides the normal code 12 or whatever it was. any ideas appreciated i cant stand seeing this thing sit here and collect dust with the amount of money already invested in it. another strange thing worth noting is that sometimes after its warmed up when you go to restart it it will idle like pure sh.t and the only way to keep it running is to rev to 2000 and then it will come outve it in about 15 seconds... ive pulled my hair out over this for months and dont know what do do when even the dynotune guy with software for handling issues like this is dumbfounded.... thanks for the help

 

Hi Bill,

Don't get discouraged.

I think the best thing you can do is get a scanner hooked up to take a look at things like the BLM, INT and O2 values. I had a similar idle issue and without a scanner I never would have solved my loping idle. I had leaking injectors richen-ing up the mixture to a point the ECM couldn't recover from. The O2 indicated "RICH" and the ECM said "MAKE LEAN," but it never could get there. It would run like poop and smell pig rich.

We can look at the BLM values to see what the ECM is trying to do to the fuel mixture. Look for a trend like...the BLM value starts in the middle at 128 then heads off in one direction and stays there.

Then look at the O2 cross-counts and make sure that it is cycling as it should. In a perfect system the O2 value is .5V and it alternates above and below .5V, in a range of 1.0V-0.1V; crosscounts refer to the number of times the value crosses the .5V midpoint.

All this requires a scanner or access to one. You can build an ALDL cable this afternoon, and hook it up to your laptop. Voila...your own scanner. Google search for WinALDL and follow the directions to build a cable.

I hope this helps.