Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
You need to replace the EGR valve. It has an internal back pressure valve that is suppose to pulse with exhaust pulses.
When it sticks it will allow the EGR to pull wide open and cause your hesitation.
Very common problem. The EGR must be the correct one. Use A/C delco valve if possible. Some universal fit EGR valve just won't work right.
To test use a vacuum hand pump to open the valve. Then start the engine . The valve should close immediately. If it doesn't it is the wrong valve or it is sticking.
Make sure the EGR valve test as I described above. I have had to replace EGR valves from after market sources due to the fact that they did not operate as above.
The EGR valve shoul lift up about half way and pulse. it should at no time go full open while setting still.
You can check your TPS sensor and make sure it reads under 1.20 v ( it automatically zeros out at idle, as long as it is under this reading)
Verify the grounds at the thermostat housing are clean and tight. Pull the bolts to and clean threads.
A fuel pressure around 6-8 psi could cause this condition( normal is 9-13)
A broken fuel pressure regulator spring could cause this to. Pinch off return line to see if this helps.
99% of the time it is the EGR valve though.
If you disconnect it does it still hesitate?
Then I would replace the EGR valve with an A/Cdelco valve. I have run into too many of these with bad valves.
This valve may just flow too much for this application,. Did you have to install washers in the valve to calibrate it. Thats is how most after market valve calibrate for different models.
Yes those are the valves I have had problems getting to work right.
You can check the other things I listed just to make sure. I still think you have a valve problem.
A/C delco valves are allot of the time less expensive than the after market valves,
And they work. they are built for application, and correctly calibrated.
As long as the computer is not setting a code for EGR then the circuit is working
As long as the fuel psi is in the specs of 9-13 psi the fuel pump is good and the regulator is good.
The injectors could be lean .Without data readings from the computer with a scan tool .
I can not verify it for you.
ok ill see what i can do thank you for your help
Your welcome, let me know what your test find out. and how it runs after you replace the valve , if you end up doing so.
Thank you and good night.
I just recently purchased a 2004 Tahoe with 155000 miles