Before we get too deep into this complex topic, it's worth mentioning that you should always check the basics when you have a performance problem with your vehicle. You'd be amazed at how just doing a tune-up on an engine can cure a whole host of problems. In fact, I’d insist that you check these things prior to your diagnosis. Check your spark plugs, air filter, fuel filter (if your vehicle has one), distributor cap and rotor (if equipped), and the oil level. Keep It Simple Stupid, the rule of K.I.S.S., is something to live by when it comes to performance diagnosis.
Many of you come to me with complex assumptions that some sensor somewhere is causing all your problems. This is the way of the dark side; avoid it. Follow the evidence, and you will find the truth. Assumptions waste your time and money. Why not start by checking the oil? On more than one occasion, an engine has had a loss of power and the cause was low or no oil in the crankcase. No kidding. Remember the movie Sling Blade? The main character, who is a lawnmower mechanic, walks over to a couple of guys working on a mower who are scratching their heads trying to figure out why a mower won't start. The main character removes the gas cap and says, "It's got no gas in it." Sure, laugh now, but the truth is you might be guilty of this very thing. I know I've been guilty of it a time or two.Check the oil, check to see if it's got gas in it, check the tune-up items, look for simple things. Don't waste your time looking for complex solutions. Just because you view a computer-controlled engine as a complex machine, it doesn't mean it is. It still needs oil, it still needs gas, it needs air to breathe and a good set of spark plugs, and it needs to be in time and mechanically sound. All those computer-controlled components are there to make sure it performs well under a variety of conditions; the engine still works the same as it did a hundred years ago. Remember, K.I.S.S. and you might just save yourself a bunch of time and money.