Thread: Car jerks and vibrates when moving slowly, hesitates when speeding up

I noticed lately that after my car warms up and you start it again you get sort of a rough idle. The car also jerks when moving slowly backing up and driving around a parking lot. Twice its even hesitated to get above 30 mph and if I'm not mistaken has some power loss around the 3,000 RPM area. My mechanic can't do anything unless that Check Engine Light is on which it isn't. Plus the car only does this once it is warmed up.

I have also noticed after the car warms up when driving fast the temperature is about quarter way up the gauge. Then if I'm driving through a parking lot or idling the gauge moves up to between the quarter and half way mark. Which placing it at about 200 degrees. I guess all cars do this because driving at highway speed puts more airflow into the radiator. When a car is idling or slowly moving temperature moves up to about 200-210 degrees then the fans go on and the car cools down.

I shouldn't be worried about that though because I hear that is normal. Plus it has a new thermostat, working CTS and doesn't have any intake leaks as far as I know.

3.8 Liter Non-supercharged 2001 Grand Prix GT with almost 144,000 miles. Has new Fuel and Air Filter, have also run some fuel injector cleaner.

I'll guess I'll have to wait for a light goes on because the auto parts store will only do a free check if the light is on. I have noticed though it only does this after a warm start, like drive the car 20 minutes, stopping the car and then turning the car back on. Especially if before the car was turned off I did some idling or driving real slow through a parking lot.

The car will also hesitate when I sat at a light for a while and the car temperature gone up. As said above excessive idling or slow driving will usually pull the engine temperature up to about 200 degrees, up from the 185 degree temperature I get driving down a freeway after the car has warmed up.

I'm leaning towards something to do with the spark plug wires or ignition coils, those parts seem to be very temperature sensitive. I have changed air and fuel filter BTW.

My mechanic had a code reader but couldn't pull anything. However AC Delco had a $2 rebate on Irridium Plugs. So I then had the plugs changed out. Now the car is as smooth as butter when hot and cold. The previous owner did a half ass tuneup I tell you what. He had 2 autolite cooper plugs mixed in with 4 original Delco plugs. Then 2 of the original Delco plugs were bad, on top of that you had 5 original plug wires and one new one.

Funny, before I had the plugs changed I even had a rotten egg smell and a CEL flash. However all is good now and the Catalytic Converter is functioning just so you know. Thank You for the advice SlowNA06.

Well my mechanic told me if your car is misfiring but nothing shows up on the computer you always start with a tune-up. He also says people often make the mistake of just throwing parts at malfunctioning cars. He is not a mechanic who works at a shop but is a trusted shade tree mechanic who is certified. Charges $30 an hour and never does unnecessary tasks just to make extra money. I trust this man over most auto repair garages and dealerships.