What To Do With My Truck?!

rgoddard57 · November 10, 2010

I have a lifted 99 Silverado 2wd with 33inch Tires 285's. It's a 4.8L auto with K&N cold air kit, PowerAid Throttle Body spacer, Granatelli MAF sensor and I have a Cortex SuperChips tuner. It has almost 254,000 miles but it has been running great up until now. Acutally it still runs great once you start it. It starts then turns off right away. Start it again it stays on. Or The first start just hold the gas just a little and it will stay on. I have replaced by the dealer the fuel pump and decarbonized the engine. I replaced the fuel filter and cleaned up the Throttle Body and Air Filter. I don't want to spend anymore money this cause Its getting to be a lot now. I have also recently bought a new car anyway but I don't want to have two vehicles since I don't need a truck anyway. Anyone know the best way to get rid of something like this? cause I know most people won't buy a truck that doesn't start the right way. I was hoping to get some money out of it but I know I might now. Any thoughts?

bluArrow · November 10, 2010

Replace the Idle Air Control Valve (IAC). It should solve your starting issue. The IAC comes into play on a cold start and allows air past the closed throttle butterfly. Once the truck is running the butterfly opens and the IAC is not needed. Holding the throttle open negates the need for the IAC. They run about $60 or so at NAPA (lifetime warranty with receipt) and take about 15 minutes to change and is held on by two screws. It should come with a new gasket, make sure the new valve has an airtight seal otherwise it can screw up your idle.

8.1HD/ALLISON · November 10, 2010

He is proably right about the idle air control valve. Once the truck is running it DOES use the IAC, hence the name idle air control valve. I'd give it a try.

nickvrebel · November 10, 2010

first thing I would do is get some pressure readings off of your fuel rail, this will tell you that you are getting proper fuel pressure from the pump (remember, defects can happen).

next - inspect your Mass Air Flow sensor. The MAF may have become contaminated over time from dirt or from excessive oiling from an oiled/ foam style filter. A bad air reading will affect the perceived air flow the motor "sees" at startup. There is a special cleaner designed for this, any auto part store will have it in stock - follow the instructions, don't cheap out and try some other type of cleaner, this is a sensitive sensor. Regardless this is a good idea for general maintenance.

after that, if the problem persists I would move on to the IAC as stated below.

Replace the Idle Air Control Valve (IAC). It should solve your starting issue. The IAC comes into play on a cold start and allows air past the closed throttle butterfly. Once the truck is running the butterfly opens and the IAC is not needed. Holding the throttle open negates the need for the IAC. They run about $60 or so at NAPA (lifetime warranty with receipt) and take about 15 minutes to change and is held on by two screws. It should come with a new gasket, make sure the new valve has an airtight seal otherwise it can screw up your idle.

partially correct.

the idle air control valve plays a roll in not only startup but any time the motor is running.

this is why the tuning of the IAC is very important in vehicles with an aftermarket camshaft.

It may not need replacement. You can pull the IAC and try cleaning it first with some carburator/ throttle body cleaner (clean the throttle body too while you are in there). It is a valve, sometimes it gets clogged.

rgoddard57 · November 11, 2010

Thanks guys for your help! I Cleaned out the IAC and the clean off the MAF sensor today. It did start stronger then again then died out again. Started again and the samething. Started again after start gave it gas and it went right up like normal then let off the gas and it stayed up at 2000 rpms! So then I turned it off. I am wondering if it isn't the throttle body. I can't find a replacement for a 4.8L its cable not electric. Anyone know if it is possible to get just the bolts? I would like to use new ones. Any more thoughts on this?