96 Suburban rough idle

[8thNote]

I have a new to me 96 Suburban K1500 with 5.7L. It has a rough idle. And it will occasionally die if the steering wheel is at full lock, in low speed parking lot type manuevers. I have an Innova 5412 code reader. It has no active codes related to engine (only air bag related codes). What is my first step in diagnosing and repairing this issue?

Thanks in advance for all suggestions and advise

 

[HotWheelsBurban]

Have any of the following parts been replaced, and when:
Distributor cap and rotor, spark plugs, fuel filter, PCV valve, throttle position sensor and idle air control valve. Are the vacuum lines connected properly, are any broken/damaged? The half ton Burbs have a vacuum power brake booster, and the line and valve on that need to be in good condition too. All these parts can affect idle and low speed(like parking). Ignition module and coil could be going bad too....All this stuff could make it idle rough, but not throw codes. I've also seen a thread where the heated oxygen sensors acting up, can create idle problems.
I'm going through a rough/surging idle intermittently on my '97 C3500 crew cab with a 5.7 Vortec. New cap/rotor/plugs/fuel filter and extra wire separators around the back of the engine (where the wires come off the distributor cap on each side) have helped, but the truck still does this sometimes.

 

[8thNote]

Have any of the following parts been replaced, and when:
Distributor cap and rotor, spark plugs, fuel filter, PCV valve, throttle position sensor and idle air control valve. Are the vacuum lines connected properly, are any broken/damaged? The half ton Burbs have a vacuum power brake booster, and the line and valve on that need to be in good condition too. All these parts can affect idle and low speed(like parking). Ignition module and coil could be going bad too....All this stuff could make it idle rough, but not throw codes. I've also seen a thread where the heated oxygen sensors acting up, can create idle problems.
I'm going through a rough/surging idle intermittently on my '97 C3500 crew cab with a 5.7 Vortec. New cap/rotor/plugs/fuel filter and extra wire separators around the back of the engine (where the wires come off the distributor cap on each side) have helped, but the truck still does this sometimes.

Thanks for the tips. I really appreciate the input.

I have no idea of the service history on this truck. I just got it a few weeks ago. I will start by checking the vacuum lines. Then eventually get around to replacing plugs, wires, cap, fuel filter, etc.

I previously owned a 94 C1500 5.7 TBI that would surge then and die under full throttle when it was hot outside. I discovered, thru trial and error on it, that the issue was an overheating ICM. The fix was to buy high quality heat-sink grease from BestBuy (designed for computer chips. costs about $15 for a small tube) and thoroughly coat the back side where it bolts to the distributor. I never had another problem after that

 

[HotWheelsBurban]

I bought my truck from the grandson of the original owner. The family had property near San Antonio, Texas and the truck apparently stayed there, to be driven on the farm, with occasional trips back to the west side of Houston where they lived. After grandpa passed, the family didn't drive it much, so it had 123,000 miles on it when we got it in July last year. We've put another 5,000 on it, including two trips to Austin and one to Conroe, north of Houston.
Because of its low mileage, I figure everything that I haven't replaced (except for the tires) is original to the truck. It had old gas in it, so I ran B12 Berrymans through the first few tanks and replaced the fuel filter. That helped tremendously with the rough idle; before that, it was like the truck had ants in its pants, it was so jumpy! I think I will probably have to replace the module and coil at some point, just due to age, but the truck runs great as long as it's not idling. So as long as it's running mostly great, I don't want to mess with it too much!

 

[Schurkey]

it will occasionally die if the steering wheel is at full lock, in low speed parking lot type manuevers.

I'd be wondering about the PS pressure relief valve being stuck, along with verifying proper operation of the IAC valve.

It'd be worthwhile to have a REAL scan tool, to verify all the sensors and computer outputs. and of course a proper tune-up.