Cold motor = Power, Hot motor = I can get out and run faster.

[BLOCKHEAD454]

I dont know why but for the reasons unknown I cant figure out why my truck is so powerfull when its cold, like it will smoke the tires, throw me up to 60 very quick, but when it warms up It falls on its face for performance and drives like a grandmas studabeger, yea I probably spelled that wrong.

Vehicle is a 1990 GMC suburban with a 350 TBI and a 700R4 trans. I have done a few things to try and resolve this issue like,

New o2 sensor, been through three diff types
New fuel pump and filter
New plugs
Vacumme check
Compression check
New cap and coil and wires
All grounds are good with continuity between everything

What else can be the problem.

 

[Spikes]

Check your EGR valve. When engine is warm, remove the vacuum line that runs to it on the TBI and plug the TBI side. If the truck runs better I would suspect a failed diaphragm in the EGR valve itself.

 

[happy 2011]

well it's not the ERG valve so don't waste your time. WOT would be fine with a stuck egr and it would stall at idle.

So it;s ok when cold. Cold means your in open loop. So computer only using coolant temp, TPS and map sensor.

Hot means your in closed loop meaning computer is listing to all sensors.
Try unpluging your o2 and driving. Most likly you have a o2 problem. I know you did 4 others but maybe a wire problem or computer. unplug and road test.

Also could be a bad cat. Lousen bolts at manifold to make large exhaust leak and road test.

try this and get back to us