hello, i own a 1985 trans am with 305 cid tuned port motor. i have just gone through a full engine rebuild and t5 five speed transmission swap about 150 miles ago. i am having a problem keeping the engine running decent below about 1200 rpm. the motor has a clevite cam ( lift = .443 intake .445 exhaust) and flat top hypereutetic speed pro pistons. other than that, all of the other internals are stock replacements. my problem= when ever upshifting through gears, the motor is fine, however when downshifting: as soon as you clutch in, the motor wants to die. also, when you come out of second from a rolling slow down, the rpms go below 500 and the motor quickly cuts off. i have gotten the car to a point where it is drivable however i did this by adjusting the throttle positioning sensor to about .81 volts (normal is about .54 for idle). this causes the car to idle very high (around 1500 rpm) when the car is first started, and then after driving for a couple minutes and downshifting through a few gears, the idle will come down to arond 750, but it is not steady (it sort of jumps up and down between 650 and 800). i was wondering if anyone who has done this swap has had the same problem. do i need a custom chip burned to compensate for the different idling characteristics of a standard trans. i appriciate any suggesitons anyone has. thanks a lot -TEAL-

 

You could try getting a TPI/5-speed chip from the dealer for your '85. That would probably solve your issue. I changed PROMs when I swapped the T5 into my SS with an '87 F-car TPI setup.

 

i was going to try that, but the problem lies in that the 1985 tpi engine package was never offered in 5 speed from the dealer. would a five speed chip from a 86 or 87 tpi computer be compatible with the 1985 tpi ecm? thanks for the help. -TEAL-

 

1985 is a junk ecm. You can't use a chip from a 86+ setup.

What you should do, is download Mike Davis's article on repinning it to a 165 (or goto a '730).


-- Joe

 

one thing, did you do the minimum idle air adjustment for it?, the tps is one part but you also have to unplug the IAC and adjust the idle screw (you may have to remove the plug) and get it to idle at 400 rpm or so. then adjust the tps for .54. when i changed to a t5 and I unplugged the IAC the idle went to 1500 rpms. i had just done the minimum idle adjustment about a month before with the automatic.

 

this may sound dumb, but did you re-hook up the VSS? If you didn't, there's your problem. You should be just fine leaving the ECM alone. Just leave the TCC harness unplugged (obviously), hook up the VSS and reverse lights, and drive. This is what I did when I swapped a T5 into my 92 Z28 with a 5.0 TPI. I didn't mess around with the ECM or chips or anything, and I have never had a problem. It idles at 700-800 RPM smooth as silk. But when I uplugged my VSS to see if I could bypass the speed limiter, I had masive running problems and the check engine light came on.

Don't forget, you also just rebuilt the motor and put a cam in a computer controlled EFI car. Chances are, your problem lies there, not the trans swap.