my68mistress

I just did a swap from LS1 to a LQ9 in my 68 Camaro. I have been reading for days and can not find anything that helps me issolate my problems so I am now asking for help. When i start my car it attempts to idle at 1300 rpm and after about 60 seconds it shoots to 2500-3000 rpm then comes back down. it does this over and over about every 60 seconds. The mods are as follows

224/228 cam
32lb injectors
ported and polished 317s
full exhaust
voodoo .650 lift springs
black bear tune
ls1 intake
cable driven ls1 throttle body polished

Any help or ideas would be great. Thanks
David

onefast84

This could be caused by a vacuum leak. I would double check and make there are no loose vacuum lines. Also a bad throttle position sensor, or Maf sensor. Try tapping on these sensors with a screwdriver handle, and see if anything changes. Also check the maf sensor to make sure it did not get damaged or contaminated with oil. Hope this helps!

dr_whigham

iTrader: (49)

Sounds exactly like a vacuum leak. Grab a can of el-cheapo starter fluid and start looking. The idle shoot up when you find it.

LilJayV10

iTrader: (39)

Has the car been tuned?

my68mistress

I haven’t got a chance to check for leaks with starter fluid yet but plan to do that today. I tried tapping the IAC and TPS with a screw driver, no change. Also tried disconnecting the IAC and still no difference. My ECM was tuned by Black Bear. I contacted him just to be sure everything was right and we didnt have any miscomunication, seems to be good on that end. My new concern about the leak is: wouldnt that raise the idle and keep it high? where as my car is going up then dropping and then going up again repeatedly. Thank all of you for your help so far.

Everett#2390

IMO, it reads like its hunting, maybe overfueling. If a vacuum leak, IAC would try to make up for it, but yes, if a vacuum leak, it would speed up.
You have disconnected the IAC and same symptom - up & down.
You do have a big camshaft and, under carb rules, the engine would need some bypass air to level out the idle and bring it down to an acceptable amount.
The ECM is trying to make up for the loss of vacuum, fueling I would imagine.
On a stock system, one would place ECM into diagnostic mode to set the IAC, as in extending and closing off the port, disconnect the IAC, undo diagnostic mode, start engine and set base idle and set initial timing with ECM unplugged. Then turn off engine, recoonect IAC, plug in ECM timing, and place ign sw in run position, eng off, for 15 seconds allowing the ECM to set idle, IAC in & out as needed. Turn off ign sw, then start. Engine should be close to ECM controlled idle and will learn as driven.

Have you tried a hand vacuum pump on the MAP sensor fooling the ECM into thinking its stock set-up with 18" of vacuum?

I think it needs alittle bypass air making up for the loss of idle vacuum.
Idle vacuum is ______?
3000 rpm vacuum is _______?

my68mistress

Again i appreshiate all of the help and i hate reading post on forums that dont give thesolution so i figured i would post an update. It turns out that my vaccum line from the intake to the valve cover was bad. I just took a few pairs of vise grips and started crimping vaccum lines to see what happen and trouble shooting with the starter fluid. now she idles at around 1100 so i will be bringing that down alittle more but glad i fixed the problem. You guys always come through when a man is in a bind.