1999 4.8L - Hard to start, rough idle, reduced gas mileage:

[rasher]

I'm sure this one comes up all of the time, can someone suggest where to start looking:

Background: 1999 Silvy w/ 4.8L V8 - 88,000 miles
No check engine light or anything like that.

Symptom 1: Have to crank the engine a bit to get it to fire (used to fire right up on first crank)
Symptom 2: Often, the engine will die right after firing, unless I rev it with the gas pedal. Have to do this for a couple two or three cycles before the engine settles down to a stable idle.
Symptom 3: The engine idles pretty roughly. I wouldn't say its misfiring, but it's definitely shuddering.
Symptom 4: Gas mileage has fallen from 18-20 average to 14-16 in the same period of time.
Symptom 5: Immediately after starting truck, especially cold, I get real jerky starts that don't feel 100% associated to a sticky TB

I am also suffering from a sticky gas pedal / throttle body, and with the information learned from other threads here, I'm considering trying to clean it myself.

I know these symptoms can indicate a number of unrelated problems, so what I need help with is formulating a step-by-step plan of attack that goes from cheap fixes and follows with more money... (I'm super broke right now...)

What I was thinking:

1. Clean the throttle body (FREE) - I read somewhere here that a varnished TB could cause similar symptoms related to jerky starts/
2. Replace the fuel filter (it's never been replaced)
3. Spark plug/wires?
4. Do I need an oxygen sensor?

What else can I check and clean that might lead to some relief? Any clues as to where to start and where to go will be greatly appreciated.

Thanks in advance,
Bob

[Austin8214]

could be just the coolant temp sensor or the egr valve. Does it run ok when it warms up?

[rasher]

Once warmed up, the truck runs fine except for the rough idle, which is all of the time. When the rpms are higher, the engine is smooth enough. Also, the hard-to-start problems happen regardless of whether or not the engine is warmed up and regardless of the outside ambient air temperature.
I have never noticed a change in the behavior of the engine temp guage.
What is the EGR valve, where is it, and what does it do? What is the maintenance of this item?

[Austin8214]

Originally Posted by rasher

What is the EGR valve, where is it, and what does it do? What is the maintenance of this item?

EGR valve is the Exhaust Gas Recycler valve. When you start you engine the EGR valve allows some exhaust gas back in the throttle body to help start the engine. The EGR vale is controled but your coolant temp sensor so that is why I said it may be that. As far as where it is located on your truck I am not sure. Look for a tube coming off the exhaust manifold and it should be on that tube some where. If you have a haynes or chiltons manual it will tell you in there. If you do not have a manual for your truck I sugest you pick one up ASAP. They have tons of good info in them.

[waitingforcolumbus]

On my friend's '99 Silverado 4.8 it was the fuel pressure regulator.
As a check, we removed the vacuum line and fuel dripped out.
It's located on the driver's side fuel rail.

[RTICWOLF]

Originally Posted by waitingforcolumbus

On my friend's '99 Silverado 4.8 it was the fuel pressure regulator.
As a check, we removed the vacuum line and fuel dripped out.
It's located on the driver's side fuel rail.

So, I take it that fuel should not be in the vacuum line then? Hmmm, I just posted for a similar problem on my 99 with the same engine and close miles, but I get the hard starting after its already been running and sits for a while only. Runs fine otherwise....although I have noticed a reduction in fuel mileage. I am welcome to any suggestions on what else it could be too.....see my post and any help would be greatly appreciated....I will check my fuel regulator tonight.

Thanks!