andrew ws6

i bought a used 52 mm holley tb with the sensors on it and put it on last night and driving it around today it through a tps code and would not downshift so i cleared and drove it home so my ? is would the tps need adjusting to my car if so how do you adjust it and what do you need to do it, it also idles a little higher than normal (1200-1300range)

Injuneer

Sounds like the throttle blades are open too far. That puts the TPS voltage above the level that the PCM wants to see for closed throttle, and will set a code. First check to make sure the cable is allowing the blades to close fully. If it is, and the throttle blade stop is against the set screw, you have to idjust the idle, IAC counts and the TPS voltage. To adjust the throttle/idle correctly:

-put a scanner on it and check the idle air control (counts). Should be between 20-40 counts. If its idling too high, it will probably read "0".

-check the idle RPM on the scanner. The tach typically reads 100-200 higher than actual RPM.

-slowly back off the throttle stop screw. The idle should drop down, and when it hits the programmed idle speed (550 in drive, 650 in neutral) check the IAC counts again. Keep backing off on the stop screw until the IAC counts come back up within the range of 20-40.

-check the closed throttle TPS voltage. As long as it is between 0.20-0.90V the PCM can baseline the "0%" throttle position. Some people like to see something closer to 0.67V. Since the TPS is not adjustable, you have to slot the holes for the screws so it can be rotated to get the voltage you want.

G. McDonald

Will this sort of condition requiring the adjustment of the TPS and idle speed (often as a result of a new TB) likely result in a rich condition at idle?

Injuneer

No reason it would make the engine run rich. Just going to raise the idle speed too high if the blades are open too far. Until the TPP (throttle position percent) reaches a high enough level to kick it into power enrichment (PE) mode, the PCM is always trying to hold 14.7:1 A/F ratio, based on O2 sensor feedback. At less than 2,800 rpm, the PCM has to see 66% TPP before it richens the mixture, at least with stock tuning.