Hello, Looking for a little help. I have a 91 silverado 5.7 350
I can't find the source of the following problem. It has a hard cold start problem (long crank time) then when warm it will idle rough or stumble/ cut out but doesn't die. It also does this on real light acceleration, the tach will bounce up and down and you can hear it. But runs fine on the highway and hard acceleration. Not sure if the starting and stumbling problems are related. A lot of work has been done to this pickup since November of 2011 so I will list them to hopefully eliminate some possibilities.
-Engine overhaul in Nov. 2011
-New fuel pump and filter
-New water pump
-Plugs/Wires/cap/rotor
-spark control module
-ignition control module
-ignition coil
-map sensor
-throttle position sensor
-IAC
-Egr valve
-Egr control solendoid
-all vacuum lines
-removed and cleaned throttle body/new gaskets
-both injectors
-Exhaust including catalytic converter and muffler
-Alternator and Battery
Tried the old trick of spraying carb or brake cleaner to find vacuum leaks with no results. No service engine light and no stored codes.
What the heck is going on with this thing? Thanks in advance for any help, Shayne

 

sounds like plug wires are out of order. or timing.

 

was a good thought, so i checked it out, unfortunately the plug wires were right

 

could this be an oxygen sensor? Bout the only thing that hasn't been changed

 

or would that set off the check engine light?

 

I have the same exact problem. It also hits second gear hard

 

Turns out the problem (for my pickup anyway) was solved by unhooking the vacuum line from the egr valve and plugging it with a screw. Not sure why considering that it has a bran new egr valve, egr valve gasket, all vacuum lines replaced, egr control solenoid. Mechanic told me what is happening is the egr valve for what ever reason isn't completely closing when it should then it sits there and flutters causing all the problems.

 

Will definately try this as soon as it daylight. Thanks