Hard start, rough idle, but drives fine. What gives?

Hi guys, I have a 2001 chevy silverado 2500 hd 6.0. Lately I have been having a hard time starting my truck after it sits awhile, I have to hit the gas to get her to go. When it does start my idle is real rough and runs at about 400 to 500 rpm, and seems like it is having a hard time staying at that rpm. Once I take off though it all runs fine...no loss of power and no stumbling. It just seems like it is starving for gas at start up and idle. I recently changed my plugs and pvc valve, but that was a couple months ago. I just replaced my fuel filter tonight but that didn't help. What do you think the problem is? I scared I'm going to get stranded somewhere I don't want to be...like my mother-in-law's or something. If it was my old truck seems like I would just adjust the carb to run a little richer, but I don't know how to do that on fuel injection..Help please! Thanks in advance for any responces.

Have you cleaned the throttlebody?

Check for fuel in the vacuum hose to the fuel pressure regulator. If you find fuel in it, the FPR is bad.

//2000CAYukon

My truck is also acting up on hard to start. I checked the fuel pressure at Idle and it read about 55psi on the gauge but as soon as I turned the motor off the pressure dropped quickly to 15psi and after about 10 min it was at zero. I suspect it is the check valve at the pump leaking. Now if I can only change that I'll be good to go.

It is getting worse now, killed on me 3 times when I let off the throttle this morning in the middle of the road. So I checked the Fuel Pressure Regulator and just decided to replace it. It didn't work. Same problem! Actually the new one made it run worse the old one so I put the old one back on. It seems like when it's cold it doesn't get enough gas, then when it finally warms up then it runs better. I don't know...I can hear the pump running and sounds strong, so I hate to drop $250 on a new one if it's not needed. So what do you think I should try next? On a note it does seem to start better in the morn when i park it facing up hill, don't know if that makes any sense, also I did replace the PCV valve 3 months ago, but don't think that would come into play here. I'm just :banghead: anymore! Thanks for any help!

You are going to need to get the codes pull before anyone here is able to give you any good help. Take the truck to auto zone and have them pull the codes. It could be a number fo things. O2 sensors, EGR, fuel pressure or MAF sensor.

Just got back from autozone, had them scan the truck and no codes showed up. Would that mean I can rule out O2 sensors, EGR, fuel pressure or MAF sensor? What's left idle air control, throttle position sensor and fuel pump.
would the idle air control show up on the code reader? TPS? That would leave me with fuel pump, but it doesn't seem to act up when it's warm which makes me think it's not the pump......Help please! Thaks guys!

Just got back from autozone, had them scan the truck and no codes showed up. Would that mean I can rule out O2 sensors, EGR, fuel pressure or MAF sensor? What's left idle air control, throttle position sensor and fuel pump.
would the idle air control show up on the code reader? TPS? That would leave me with fuel pump, but it doesn't seem to act up when it's warm which makes me think it's not the pump......Help please! Thaks guys!


this could be the ECT....this can trick the computer into thinking its minus 40 below or 180 deg f as the engine temp...

if this sensor is out of range no codes will be generated...poor cold start,,,but after warm up runs ok...

this can be checked with an ohmmeter to verify its failure..

buy new one and measure the resistance before installing with the engine cold and the purchased new ECT..compare...

mine is kinda doing the same thing...after it sits awhile...the first turn of the key it will just keep turning over, then when you try it again it fires up immediately...i cleaned the throttle body, & MAF sensor, and its not throwing any codes. What do y'all think?

what is an ETC?

what is an ETC?


ect =engine coolant temperature..
with what I stated before this should be checked out...

don't know what it is or looks like ????
go find the part on line then find it on engine...

Coolant Temperature Sensor Resistance Test:


1.With key off, disconnect connector from coolant temperature sensor.
2.Connect ohmmeter across coolant temperature sensor. Resistance should read as follows;
•700 to 1,000 Ohms at approximately 200°F (operating temperature).
•7,000 to 13,000 ohms at approximately 70°F, (room temperature).
3.If resistance is not within specifications, replace sensor.
As always, check the service manual for the proper procedures and specifications for your particular vehicle.

ok so I just hooked up an fuel pressure gauge to my fuel rail and turned key on, I had 50 psi with the key on then with key off the psi dropped steadily to 9psi within 10 minutes. It was holding at 50 psi with engine running, and of course it wasn't acting up, it was running pretty good. Go figure huh? But asside from that I don't think my psi should drop that much that quickly within 10 minutes do you?

ok so I just hooked up an fuel pressure gauge to my fuel rail and turned key on, I had 50 psi with the key on then with key off the psi dropped steadily to 9psi within 10 minutes. It was holding at 50 psi with engine running, and of course it wasn't acting up, it was running pretty good. Go figure huh? But asside from that I don't think my psi should drop that much that quickly within 10 minutes do you?

the spec. is 53-62 psi,,should hold pressure for 10minutes ..not drop off rapidly...on shut down

looks like a bad pump///

how can i check mine? Like does Autozone or Advance Auto Parts carry a fuel pressure gauge so i can test mine?

Just put in new Fuel pump and put the relay back in and now the pump doesn't run at all when I turn the key. I ran most of the fuel out before I did this, is there a safety switch that won't let the pump run if fuel is too low? Maybe it's too low for the new one. If now what do you think I did wrong? I made sure that it is getting good ground by filing the spot where it is screwed to the frame. Hooked up my pressure gauge even and no PSI.

Will it run until the system is pressurized or will it only run for a couple seconds either way? In other words if I turned the key to run and went down to mess with the wiring will it run once it makes contact say 2 minutes later if it not making contact somewhere?

Silverado dude-- you can rent a pressure gauge from Auto Zone.

if the pump does not run make sure the fuse is not blown,,,do you have a meter ??I hope so if your working on vehicles..make voltage checks...make sure wires did not get damaged etc....

when the ignition is on the pump runs for 2 seconds....you should have like 5 gallons of fuel ready to install into the tank before driving the vehicle to the gas station..

with little fuel in the tank testing the pump is fine but not for any lenghth of time,,as this is how many pumps die an early death..

I did check the fuses..they are ok. I do have gas ready to put in, but don't want to yet in case I have to drop the tank again.

Any idea how many volts should be going to the pump? 12?

Thanks for the reply, Hopefully I can get back to it today and let you know what I found.

ok so I pulled the pump back out and it is running, I put it in a bucket of gas and it did pick up fuel into the clear tube that goes up to the top of the unit. But it wasn't spitting it out by any means. Does the pump have to be primed first? I put it back in the tank and the tank back on the truck and everything hooked up and have been turning the key on and off trying to get the fuel system pressurized, but am still getting no psi on my gauge. What am i doing wrong? is it a bad pump?