1993 GMC 5.7 TBI Strange Idle/Driveability Problems

[93SierraZ71]

So my '93 Sierra has a seemingly unsolvable problem. It has been to 4 shops, a GM master tech I know personally and my dad and I have tried to figure this one out. When you start the truck cold, usually it starts then stalls within a second or two, sometimes takes 3 or 4 times to stay running, then the rpms go up and down and it lopes like crazy. Then when you drive it, it bogs down, then after about 5 seconds has full power. If you just floor it, it goes up to about 4500RPM then shifts hard and bogs down again. If the motors hot and has been running awhile it idles and drives perfectly fine, except for a recent vibration and loud noise from under the floor. It has been doing this for about a year now but cant figure it out. I have replaced every sensor and checked for vacuum leaks a hundred times and every thing is fine. I replaced MAP,MAF,IAC valve, distributor, plugs and wires, changed injectors, changed throttle body and gasket, valve timings good, ignition timings good, has new ignition coil, checked PCV and EGR valve, I checked fuel pressure and changed the fuel filter... I love this truck and it has never let me down except for this. It had a hard life before I got it and it currently has 405,000 Kilometers on original 350 so I'm not sure if its just had enough or if it can be fixed. I'm really hoping you guys can help me out here!! If you have any ideas, feel free! Thanks

 

[magimerlin]

Have you checked and or replaced the coolant temp sensor.not the one on the side of the block as that's for the temp gauge..... it's not mentioned to just checking....

 

[great white]

sure sounds like ECT sensor....all things being equal.

 

[TylerZ281500]

i know alot of pople say theyve gone through the exact same thing, but i went throught the exact same thing, i had a bad computer bad knock and multiple breaks in my harness that would trick me into telling me all was ok

 

[TylerZ281500]

is it throwing an esc code at all?

 

[93SierraZ71]

Have you checked and or replaced the coolant temp sensor.not the one on the side of the block as that's for the temp gauge..... it's not mentioned to just checking....

I replaced the coolant temp sensor.

 

[93SierraZ71]

sure sounds like ECT sensor....all things being equal.

I replaced the Throttle Position Sensor recently even though the old one tested fine.

 

[93SierraZ71]

is it throwing an esc code at all?

The SES light comes on every once in awhile. It's a code 43 I believe lean exhaust, yet the exhaust smells very rich.

 

[TylerZ281500]

hahahahaha i think code 43 is esc, check your knock sensor

 

[93SierraZ71]

haha I'll see about replacing the knock sensor today and see what happens. Hope it fixes it.

Bryan