2002 Chevy Impala 3.4L V6 Automatic transmission 165,000 miles
I have no throttle response over 40 mph unless floored. The engine seems to be bogging down. From take off to 40 mph the car runs great, although the idle seems to have a slight hesitation to it. The oil still looks new, no chocolate milk in the oil. Heater puts out hot heat.
I have replaced the catalytic converter, plugs, plug wires, throttle positioning sensor, fuel filter, downstream O2 sensor. Also, there is NO check engine light at this time.
I had Firestone here in Ohio flush and fill the coolant system. A local transmission shop said it is not the transmission, but rather the engine.
In a case like this, it is best to default to the basics. Hook a vacuum gauge to the engine while its running. If you want a strong steady reading more than 15 inches of vacuum. Remove all the spark plugs and run a dry and then a wet compression test. If you have a low cylinder, 15% less than others and an oil squirt brings it up, the piston rings are worn out. Post the readings here.
If you don’t have these tools or know how to run these tests, might be time to pay a pro.
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Time to stop Easter-egging (guessing at what parts to replace) and go to a good auto tech shop. The technician will drive the car and read engine diagnostics in real time. He can tell whether the problem is fuel starvation, sticky injectors, ignition breakdown, or something unusual like a cam-angle sensor and tell you exactly what part to change. This will probably cost around $75 (at least here in NC) and be worth every penny.
There are a lot of engine problems that show up this way but do not set permanent P-codes.
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The intake manifold gaskets were a trouble spot with these engines. If yours has been breached it could be allowing extra unmetered air into the engine, which could cause it to run poorly.