GM 3400 engine surge

[Blazerguy1983]

I have a 2003 grand am with the 3400 engine and 4 speed automatic with overdrive. It has 98k on it. The plugs and wires where replaced not long ago. I started noticing in overdrive on a straight stretch or sometimes in 3rd I would get a slight surge up in rpm while driving Down the road. More so when the engine is warmed up.

Now it is surging up and down 1,000 – 1,500 rpms at idle in park. Stops surging in drive gears. No codes. Any ideas?

Topic

[dan]

a common issue with these transmissions that can cause “surging” is the torque converter clutch, this takes the torque converter and eliminates slip buy locking it up, making everything direct drive when you are at steady cruise, saving on gas, issue is the torque converter clutches in these cars have a nack for acting up, they will kick on and off when you drive, and you will notice fluxuations in RPM just like you are experiencing, i have noted that sometimes it may or may not throw a code.

this is particualy the case when the engine has warmed up, because this is when the torque converter clutch is told too engauge, when it hits closed loop and the engine and trans are at op temperature, too optomize fuel economy, but this is typically at a steady cruse when the transmissions torque converter clutch is told to engauge and diengauge.

surging could be vacuum leaks, i would suggest checking for vacuum leaks if the idle is going up and down, but typically with that you would throw a code, unless you had a slight vacuum leak, sometimes when the lower intake manifold gasket is about to go, it will cause drivability concerns, my old buick had a slight miss when its intake manifold gaskets started to leak.

also make sure you have plenty of coolant in your cooling system, and that it is well bled.

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