Hello

I'm going to give a few things to check on your own. We both know this vehicle has been to the shop three times therefore it's a tough problem. I'm giving you basic things that could cause the condition you have.

Fuel Problems & Related Issues: In recent times, I have seen many problems with fuel filters clogging, poor running conditions and other fuel related issues. This is due in part form the rise in fuel prices and demand for fuel. Some service stations have run out of fuel several times over the last few months. This is where some of the problems start; we are at the bottom of the tank where the water will be found. Moisture and condensation plus any water that may be part of the delivery will find its way to the bottom of the storage tanks. In some cases, the water will rise above the pick-up tube of the tank and mix with fuel that enters your tank when you re-fill your vehicle. This will definitely create a problem with engine resulting in poor performance. The only way to correct this problem is to remove all the contaminated fuel and renew with good fresh fuel. (I recommend that a trained professional perform this task to eliminate possible injury.) Another way is to let the fuel cycle through the system while suffering with poor performance and the possibility of replacing your fuel filter in the process.

Fuel System Warning: If you perform any type of work to the fuel system, including a fuel filter, it is recommended to use extreme caution, Wear Eye-Protection, Nitrile Gloves (unless allergic) and keep a Fire Extinguisher close by. Gasoline is highly flammable and dangerous, use extreme caution. If you are not confident, rely on a trained professional to perform the diagnostic work or repair.

Something else to consider:

Coolant Sensor The water temperature sensor communicates information to and from the computer. If this has failed to work properly, it would definitely create issues like the one you described. Before we condemn the sensor let’s make sure the coolant level is correct and the antifreeze is properly mixed. The antifreeze should be 50-50 one part antifreeze and the other part water. If the mixture is wrong, it could affect the sensor. Most people do not pay enough attention to this little device, which can give you many problems. Learn more about Coolant Sensors, Click on the link provided below…

http://www.mightyautoparts.com/pdf/articles/tt67.pdf

Another thought!

Chevron Professional 3-Step Fuel System Cleaner
Chevron Professional 3-Step Fuel System Cleaner provides three critical engine cleaning formulas in an a three-step application.

§ Step 1 – TECHRON Concentrate helps clean deposits from fuel injectors, carburetors, ports, valves and combustion chamber. It also reduces knock, ping, and run-on and helps lower emissions.

§ Step 2 – Induction Cleaner helps remove harmful carbon, varnish and gum deposits

§ Step 3 – Throttle Body/Air Intake Cleaner cleans throttle body and air intake systems