1999 silverado wont idle when cold

My 99 silverado will not idle when the engine is cold. The engine rev's between 300-1200 rpm and misfires bad. After engine warms up to normal operating temperature it runs pretty good. It does however have a slight skip when idling with engine warmed up.
If I start the truck and drive immediately with out warm up then the first time I slow down the engine will rev between 300 and 1000 rpm's in gear.
I have changed air and fuel filters, spark plugs and spark plug wires, the chevy dealer has cleaned the fuel injecters two times. The check engine light comes on and off every one in a while. Indicates bank 1 and bank 2 too lean. This light is intermittent. The engine is a 4.8L. Thanks for your help in advance.

Have you had the fuel pressure checked?

spray some carb cleaner around the base of the intake manifold to see if the manifold gasket is leaking, other than that could be hundred different things, if you live in dallas I could look at it.

i HAVE THE SAME PROBLEMS, I CHANGE OUT THE FUEL PUMP DIDNT IMPROVE MUCH, IM WONDERING IF THE PRESSURE REGULATER MIGHT HELP ALSO USED AS SCAN TOOL SEVERAL CODES CAME UP , TPS, O2 SENSOR, RICH PASSENGER BANK,MISSFIRE ON 4,6,8. IM THINKING OF CHANGING OUT THE FUEL PRESSURE REGULATER, IF THAT DOSN'T WORK ON TO THE TPS.

Fuel pressure is good
Carb cleaner made no difference
Cleaned the idle air control and throttle body with
carb cleaner. No change
Thanks for the tips anyone have anymore? Bubba14

I just replaced th fuel pressure regulater, what a difference. 100 big ones, truck runs perfect and the check engine light went off.

That's great Poncharelo, :grinno: I wish mine would be that simple. This morning with a temperature of 17 deg. outside my silverado would not idle without help from me with the gas petal. After the engine warmed up it ran fine. I am still checking with ohm and amp meters. I just can't afford another high priced check by a chevy dealer with no fix. Already been burned three times. :banghead:

I t almost sounds like your O2 sensor is bad, fuel pump relay, or regulator. The computer is supposed to monitor fuel and ignition in a Open Loop until it receives a signal from the O2 sensor for 10-30 seconds (cold start). You really should try to go by a Advance Auto, or Autozone (or equivilant for your area) and get them to pull codes for ya -for free. They should also help you in checking the output of your sensors to see if they look okay. It IS a sale for them...... Have you cleaned TB lately? I've heard of that fixing these type of problems as well. Best of luck, and let us know what you find out.

I have been experiencing the exact same problem, but hopefully got it fixed today. The ERG valve was stuck open. Once it was replaced, about $270, the problem has so far gone away. I am now trying to figure out the wheel sensor problem that causes my abs to go out. any suggestions?

I also have been experiencing the same problem with my 1999 Silverado. Light came on about a week ago. I took it to the dealer and forked out 270.00 for a fuel injection service. Light was off for two days and just came back on yesterday. I took it to AutoZone and they hooked it up the the computer and got the reading that banks one and two were burning lean, which is the same thing the dealer told me. Dealer wants me to bring it back in, but I don't want to go back and forth with them while they try to figure out what went wrong. Rushingm any updates on how your's is running since replacing the ERG valve?

My codes are 171 and 174 too lean bank 1 and 2 as well as misfire on cylinders 5 and 8.
I have now changed the idle air control sensor and did NOT improve anything.
Engine still surges.
Check out the post by timber3 yesterday.
He describes the problem as well as it can be described. Exact duplicate of my problem.

And about the ABS problem check the post on 1-23-2004 by jumpingjack66 you might find some help there.

Bill,

Mine has run perfect since that EGR valve was changed out, so far so good. Also, the mechanic told me that valve being stuck open would cause it to run lean, so you might have the same problem. Didnt take him 20 minutes to change it, so it might be worth looking into.

Took mine back to the dealership for the rough idle and the 171 and 174 problem codes. Just got a call from them saying the problem was the intake manifold gasket. They changed it out and say everything is good to go. I won't pick it up until tomorrow, but I will repost when I find out if this fixed the problem. Now I get to go back and forth with them to see if I can get my money back on the injection flush that I didn't need.

Forgot to mention that the intake manifold gasket would make sense seeing that the idle was much worse when it was extremly cold. As the gasket warmed up it expanded and the vacuum leak would become less significant.

Turns out that it was the inake mainifold gasket. Dealer replaced it and the mis-fire codes cleared up and the truck is running greate.

I am taking mine to the chevy service department this afternoon.
I sprayed a little starting fluid on the intake manifold gasket seam and the engine smoothed right out.
I should have listened to 99ssconv back in Dec.
Well I did sort of, I sprayed carb cleaner but it was the non flamable type so it didn't make any difference in rpm's, but the starting fluid showed up real quick.

It's fixed! Got the intake manifold gasket changed and engine runs fine even when cold. Misfires gone, rpm surging gone, Thanks for your help. Bubba14