Review on ACDelco 217 3349 Original Equipment Injection by Dave Hersma

For over a year now I have been experiencing a situation where the engine RPM drops too quickly when coasting e.g. when engaging the clutch to brake, sometimes, usually during a stop . signal or stop during warm-up, the idle speed drops to 500 rpm for about a second and then quickly rises back to 750 rpm. This issue resulted in the check engine lights or codes not being stored, but I knew from experience that this type of idling is not normal considering this truck has clocked up 66,000 miles. After learning how throttle design works, I learned that the two main inputs the computer uses to determine idle speed are the mass airflow sensor and throttle position. On older models, the throttle position switch can be removed separately, but on the Colorado TPS it is built into the throttle body. I've read Colorado enthusiast tutorials and tried cleaning the MAF and throttle body but it didn't help. Changing the MAF greatly improved idle stability, but the situation where the idle dropped too quickly persisted. Locally the throttle body is terribly expensive, over $200, it was worth trying to snag it for less than $70. This part is a genuine Delco AC replacement, not an aftermarket. Installation is not easy, we remove the air duct, remove the air resonator with a 10 head, remove three vacuum tubes from the resonator and unscrew the throttle body mounting bolts with the same 10 head, disconnect the fuel vapor intake pipe, the clamp can be loosened with your fingernail will. The hardest part was removing the 8 pin TCA connector, it breaks easily but can be removed by prying up the locking tab with a small flathead screwdriver. installed a new throttle body gasket, cross torqued the mounting bolts to 80" per the alldata service manual. After installation, let the truck idle for 5 minutes and then drive on the highway, exit the highway and let it stand for 5 minutes again. This is required to allow the computer to relearn the parameters of the new TCA. This solved the problem, idle is stable at 750 rpm, idle drops to 1100 rpm when coasting and only to 750 rpm at 10 km/h, idle no longer drops to 500. Even seems like the engine has less vibration at all speeds. The lesson I've learned is that even if the check engine light doesn't come on, which is what the dealer is looking for, the TCA may not be up to spec, and at this price point if cleaning the original doesn't do the trick, it's worth replacing. I do not work. My advice to anyone considering this service is to replace the MAF first and then the TCA if necessary. Purchase a throttle body gasket as the TCA replacement will not include a new one. You will need a torque wrench calibrated to lb-in as the TCA is attached to a plastic manifold and over tightening can damage the manifold. You may also consider buying an actual electrical connector removal tool, as the connector itself can be even more expensive than a TCA if you damage it, but if you're careful with a mini flathead screwdriver you can pry the bracket up. and simply remove the plug. Overall this throttle actuator was a great value and I saved a lot of money by not having to go back to the dealer.