Replacing engine on 2004 Chevy Trailblazer

If it can only go 30 mph, there is something wrong. Replace that cam shaft sensor and see if that helps. But the carbon build up story is pure BS in my 50 years experience on engines of all kinds. Carbon where, ask him? Carbon is a by product of combustion when fuel is burned with a shortage of oxygen. These newer engines run so darned clean......carbon build up ain't gonna happen! Find a new repair shop.

Thank you for your response.

Your mechanic is not as "Trusty" as you Sandra. I hope the best for you. And not to worry.

The vvt solenoid locates just under the cam position sensor can cause this symptom as well.. weak coils or burned out coils is a huge problem with trailblazers..all of them. To test coils, while the engine is idling just unplug the connector from the coil on top the valve cover. Weak ones won’t change the idle much and obviously burned out ones won’t change a thing. Run Lucas fuel treatment in every tank of gas (3 oz / 10 gallons mixture) it runs about $9 per 32 oz bottle at Walmart. Bad gunk build up that’s visible on the cams when looking into the top through the oil cap..it’ll be black spots on the interior of the cams and inside the oil feed and cap. Run synthetic blend oil in these motors because they don’t break down and cook like traditional oil does. You can get over 10,000 miles per change with syntech blend where traditional oil will turn black within 3,000 miles. Keep the oil clean and full to keep the vvt solenoid functioning well. And check coil gaskets every so often especially in climates higher in precipitation. If u see any cracks on the coil gaskets, u can get new gaskets online and In stores. I used chapstick on both sides of the gaskets so it sealed well with some water repellent on both the valve cover and the coil itself. Petroleum jelly or something similar works too but just a small amount. These motors have aluminum blocks and are high maintainance because of how the aluminum shrinks and swells with heat and cold.

The throttle body can build up carbon after so long...seafoam makes a throttle body cleaner that works well..just get to the throttle body where u can see the flap move on accelerating the fuel and spray the seafoam into it. It’ll blow black and nasty for a bit but just keep it running by having someone push the gas when it tries dying. They say not to do this but that’s bull..to relearn ur ecm /pcm..unplug the battery for a day if possible two days then plug it back in and drive normally on the hiway and in town...this lets it learn how u drive and resets all the data needed. Mechanics charge a fortune for the work and on these trucks it’s way too simple to justify the cost. Maybe worth the prices when working on front wheel drive dohc motors like Chrysler but not these motors. I’m a 5’ tall woman and taught myself thru YouTube..books.. and trial and error. It would have cost over $10,000 for a mechanic to do what I’ve done on $500. Sorry guys but look at our economy..somethings gotta give cuz too many can’t afford that ona truck so low in value.

I was told I would need an engine replacement if my Trailblazer continued to idle roughly. Before I knew where the cam sensor was, I coughed up $300 for it to be replaced. It was a $70 part that I could have done myself. Shortly after the rough idle continued. I purchased engine flush and did an oil change. Problem solved. Was pissed at the mechanic for not having suggesting what I did. He went big without a simple solution first. Always get an second opinion.