I just installed the gm 847 cam in my car as well as a turbo 350 and Im having some issues with the idle. The turbo 350 has a reverse pattern valve body with a t-brake and a 3500 stall and I had pcm for less take out the transmission program and tune for the gm 847. Whats happening is this, the car idles fine when in park and in 1st with brake applied, problem comes in when decelerating just before coming to a stop. it will die unless I feather the gas untill fully stopped when fully stopped idle recovers to 900 rpm.I adjusted nothing on the car from my cc 305 except the pcm mods,have any ideas as to what to look for? by desighn the trans brake has no engine braking on deceleration so it should idle like a champ with no load right?Is there a low vacuume condition with this cam that causing problems? tps sensor maybe? really Im lost on this one any help would surely be appreciated.

 

It's the manual valve body that causes it to have no engine braking on decel.

Do you have the speedometer hooked up and working correctly? There is a table in the PCM that holds the closed throttle idle speed higher than normal when the car is moving = a non-0 signal from the VSS.

 

Ahh... no speedometer is not hooked up,you think thats the cause? How did you interface your speedometer on the 400 to the factory pcm,does someone make a kit? any way for a temporary fix?

 

Fred-
I also have a similar problem with my car, only it wants to idle at ~2000rpm (on the tach) while coasting. It doesn't drop untill I came to a complete stop. I have LT1Edit, but I'm just learning, so can I fix it with that?

I know it's a problem with the tune, because if I put my other PCM in that was tuned by Ed Wright, the problem goes away totally.

Can you help?? Thanks!!

 

I want to hear the answer to that one, as well. I've been driving around since last fall without a speedo. It only bothers me when Johnny Law follows me when I'm not in traffic. I have to guess where I am based on my rpms, which is tough with a high stall TC.

 

I figured it out guys if you get a sending unit from www.dakota digital.com part#I think sen 1-01 it transfers the mechanical signal to a digital one the pcm can translate it was only 25.00

 

My TH400 has a 40-tooth reluctor gear on it, and a VSS sensor from a GM truck.... all you need to do is tell the factory PCM you are running an automatic (40-tooth wheel) instead of an M6 (17-tooth wheel). I don't use the stock PCM for anything but the speedo and the IAC, so its no problem to have all the codes for the missing 4L60E functions.