Engine 1989 Fox has hesitation (Stumbles) around 3K and under acceleration

Hello All,

This is my first post here. Unfortunately it comes with a problem lol.

So I picked up an automatic Fox body with 78K miles a few months ago bone stock down to the smog pump with the intent of going 5 speed and restoring it to its glory. With that, The car seems to have developed an intermittent stumble.

The car idles like a champ and actually drives very good with the above exceptions

When I picked up the car I did the basic tune up things
-- cap rotor
-- Accel coil
-- plugs
--performance wires
-- 140 amp alternator
-- replaced the fuel pump and filter did a fuel systems flush.
Then I added
--BBK CAI
--3:73 Gears (whole real axel seals and bearings replaced also)
-- off road H pipe
-- FLowmasters

This issue has come and gone since I bought the car but seems to be hanging around now.
under acceleration the car stumbles here and there and seems to lack low end grunt.. at times when i take off it seems to struggle at low end almost like the car is missing, then it goes away slightly or completely at cruising speed, but comes back when the car starts rolling again.
when idling i can rev the car and around 3K then needle bounces and seems to hesitate as if it hits a brief wall and then continues (if needed I can upload a video).


I ran a KOER and KOEO test with an OBD1 scanner and all that was bad was the IAC which I replaced and the code went away.

SO at this point I am at a bit of a loss. I am starting to think the TPI module or Distributor may be to blame

But before I start throwing money at it I'd like to know a few things to check. Even though the car is an automatic, i'd like to think it should have more balls then it does LOL

appreciate any insight from the 5.0 gurus
 
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Upon testing the TPS the voltage reading at idle was off a bit suppose to be under 1v reading closer to 2v so I have a motor craft one coming. Gonna start there everything else has either been checked or replaced aside from the timing with the spout in. I did advance it to a conservative 13 from 10 when I did a tune up. Engine didn't mind it at all
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Acceptable TPS voltage range at idle is 0.5 to 1.25 volts. Anything in that range is good.

I'm leaning this being something in the ignition. PIP, TFI or coil

When i had this issue with my car, it ended up being the Accel coil.
 
Ok, figured I'd update. Changed out the TPS sensor, with an OEM MotorCraft one, ensured it was calibrated to around one volt. This fixed the problem car has balls again. No stumble at 3k low end torque is back. Thanks for all the help.
 
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