2003 Silverado 1500 with 5.3 idle surging

I have a 03 Silverado with 180k on it. It has always ran great but the other day...it is very cold here and I got it out of the shed and it started, "having a fit" as my wife puts it. It does not want to idle very good. The rpms go up and down. This seemed to correct itself after it warmed up for a few days then it got worse and set some codes. I call my mechanic and he said to clean the mass air flow so I did. Same thing. So I replaced it with one from O Rileys. That didn't help it either so I took it in to him. He said the fuel filter was clogged up and he cleaned the Throttle Plate up. Cleared the codes and said that should fix it. It didn't...still idled bad but not all the time just sometimes it "has a fit". Code came back and he checked it and said it was one of the cats. Said to drive it more and see if it comes back. It has not came back on but it still has fits on me. Sometimes smooth as glass and sometimes it will almost die and rpms jump all around. If I touch the gas with my foot it straightens out imedeatly and runs smooth.
Any ideas? I'm handy with cars but don't know what to look at.
Rob

Alittle update...on the way home the service light came on and it has 3 codes now. P0101, P0171 and P0174. It is sill idling funny but seems better now that the light is tripped. I left the codes stored so the mechanic can look at it but would really like to just fix it myself. Any ideas?
Rob

I have a 03 Silverado with 180k on it. It has always ran great but the other day...it is very cold here and I got it out of the shed and it started, "having a fit" as my wife puts it. It does not want to idle very good. The rpms go up and down. This seemed to correct itself after it warmed up for a few days then it got worse and set some codes. I call my mechanic and he said to clean the mass air flow so I did. Same thing. So I replaced it with one from O Rileys. That didn't help it either so I took it in to him. He said the fuel filter was clogged up and he cleaned the Throttle Plate up. Cleared the codes and said that should fix it. It didn't...still idled bad but not all the time just sometimes it "has a fit". Code came back and he checked it and said it was one of the cats. Said to drive it more and see if it comes back. It has not came back on but it still has fits on me. Sometimes smooth as glass and sometimes it will almost die and rpms jump all around. If I touch the gas with my foot it straightens out imedeatly and runs smooth.
Any ideas? I'm handy with cars but don't know what to look at.
Rob

the mileage your at and not replacing the fuel filter at 30-40,ooomiles puts stress on the fuel pump..I WOULD CHECK FUEL PRESSURES ... must be 53-62 psi. if the pressure is below this replace the fuel pump and the fuel pump relay..

also replace the ECT sensor ..this and the connector to it may be defective.

what are the dtc 's with this ?

Idle speed is regulated by the IAC not the MAF. the maf senses air input to help pcm control fuel mixtures. with a bad maf the engine will not run correctly and also effect shifting..

the IAC can get dirty or worn. this should be removed and cleaned with throttle body cleaner and a tooth brush...same as throottle plates. never use carb cleaner as this is destructive to the non metal components...wire,plastics,gaskets,rubber....etc.. ...

IAC varies the air input to the intake to adjust idle speed ..should be steady at 650RPM.. check intake hoses for leaks..

the mileage your at and not replacing the fuel filter at 30-40,ooomiles puts stress on the fuel pump..I WOULD CHECK FUEL PRESSURES ... must be 53-62 psi. if the pressure is below this replace the fuel pump and the fuel pump relay..

also replace the ECT sensor ..this and the connector to it may be defective.

what are the dtc 's with this ?

Idle speed is regulated by the IAC not the MAF. the maf senses air input to help pcm control fuel mixtures. with a bad maf the engine will not run correctly and also effect shifting..

the IAC can get dirty or worn. this should be removed and cleaned with throttle body cleaner and a tooth brush...same as throottle plates. never use carb cleaner as this is destructive to the non metal components...wire,plastics,gaskets,rubber....etc.. ...

IAC varies the air input to the intake to adjust idle speed ..should be steady at 650RPM.. check intake hoses for leaks..
2003+ Have drive-by-wire with the electronic throttle body. Which means the TPS could be failing.

Do check the TPS (Throttle Position Sensor) as wel as the IAC (Idle Air Control). One or both could be at fault. Symptoms you described match the diagnosis for TPS or IAC failure.

no IAC with drive by wire, its all integrated with the t/b. I would also check the intake gaskets b/c when they are bad they leak when cold.

It is very cold today at -1 F and we have 8 inches of snow with more today so had to drive it again to get to work. I'm trying to get it back into the mechanic today. I know he cleaned the Throttle Body. I'll ask if they checked the fuel pressure. He did look for vac leaks but then said something about the intake might be leaking but it seems like he would have checked that. It does it all the time now...I have to drive with 2 feet and keep giving it a little gas to keep it from freaking out. The headlight go bright and dim and the rpms jump all over. Just off idle it runs fine with no problems at all.
I was going too look at it last night myself some but it is soooo cold and I didn't feel good.
So, the last post said NO IAC with drive by wire? So is the part on the foot feed something that would cause this? This truck has never has a very good cruise control. It has always "surged" when you have the cruise on like when you come off a hill. I don't know if this is related but if you drive with your foot it does not do that.
New Mass air flow sensor so I don't think it is that.
Thanks for the help. If I can't get it in today to the dr I'll be looking at it this weekend on my own.

Alittle update...on the way home the service light came on and it has 3 codes now. P0101, P0171 and P0174. It is sill idling funny but seems better now that the light is tripped. I left the codes stored so the mechanic can look at it but would really like to just fix it myself. Any ideas?
Rob

since you have a p101 code this is from the maf signal being incorrect..the maf is defective or you have a leak from the maf to the intake manifold.

usually the engine runs poorly and the transmission shifts harsh ..

as was mentioned the throttle body gasket can leak..

the tps being bad would cause low power mode to come on so I doubt it is the tps. if you can drive above 20mph the tps is good..

could very well be the intake manifold leaking..also ...

Thanks for the advice...didn't get back into the shop today so I might do some checking on my own this weekend. I already repalced the maf sensor and that didn't fix it. With the 180k on it I'm betting it is the intake gasket now too. I think I can replace it myself. I drove it at lunch and it ran pretty good. The warmer it is out the better it runs.

Intake job on these is pretty striaght forward. Dry intake but you have to pinch off the coolant hoses that go to the t/b. prob like and hour in the driveway if you have all of the parts. Also the intake itself can tend to warp on these. Dorman sells a complete kit if you need an intake.

Well I did the intake over the weekend and that seems to have fixed the problem. I didn't drive the truck much after the repair but I think that fixed me up. I will say it is for sure fixed in about a week of no problems. LOL
Your right the repair was really pretty easy. I have one question...the hoses to the throttle body had no coolant in them. Neither one of them did. Any idea why? I'm wonderin if I have a clog or something?
Rob

Its a high point in the system so when the coolant contracts it will drain some. Just make sure your coolant is topped off.

Ok that's what I was thinking/hoping. When I took the first hose off there was quite a sucking vacuum noise from it.
Thanks again for all of the help,
Rob