Question1994 K1500 p/u. 5.7 motor, auto trans. Problem with smooth starting and smooth takeoff. Truck needs feathering of the gas to keep running on a cold start (warm start okay). When taking off, engine hesitates and stumbles until foot is too the floor, then it takes off fast. Once it hits 35mph, it runs well with passing power, but not quite the power potential that it should have. This problem happens warm & cold. Timing set a 0 degrees with timing wire under glove compartment disconnected. Recent replaced parts include Fuel filter, ign coil, cap, rotor, wires, plugs, ign module. Fuel pump pressure checked at 13.5lbs good. Injectors are spraying good & evenly. TPS checked out okay. I'm at a loss of what to do next.
AnswerTry something simple like disconnecting the vacuum hose to the egr valve and plug it. Cold start the engine/road test and check symptoms. If better EGR valve may be defective.
Does the engine have a high idle when cold...Check the IAC system. May be a defective IAC.
Pick-up coil in the distributor can also cause stumbling on accel. Check for heavy corrosion...replace as necessary. If vehicle has a lot of mileage it may just be better to replace the entire distributor.
Make sure no spark plugs were cracked during install.
I have had injectors cut-off intermittently causing similar conditions.
Check vacuum leaks including PCV valve.
Before doing all this I suggest cold starting and road testing with a scan tool connected and scan live data while problems are acting up. TPS may have a bad spot dropping out. I know you said it was already tested thou.
Get back to me if you do not come up with anything.
