Engine surges when in idle in drive?

Let me know what you find.

Joe

The torque converter is unlocking intermittently. The most common cause is the brake light switch is out of adjustment. Less common, there could be a bad spot in the throttle position sensor. First try holding the brake pedal up with your foot. If that helps, readjust the brake light switch. Mechanics use a scanner to view live data, and that will show the state of the brake light switch, the signal voltage from the throttle position sensor, and other things that can cause the torque converter to unlock.

When this problem is not occurring, you can replicate it by driving at a steady highway speed, (not with the cruise control), hold the accelerator pedal steady, then tap the brake pedal with your left foot. You'll see engine speed increase 200 rpm, then drop back down a couple of seconds later. You'll feel the torque converter lock and unlock too.

On Chrysler products, other than diesel engines, you'll never solve a running problem by replacing the fuel filter. They easily last the life of the vehicle.

You would do well to throw that cool air intake system away. Liquid gasoline does not burn. It has to be turned into a vapor to burn. One purpose of all intake systems is to warm the air so that happens faster. The thinking of the people who promote these things, as long as you have money they can get from you, is colder air is more dense so more can be packed into the cylinders, then you add more fuel to get more power. The rest of us do the same thing by pressing the accelerator pedal further. The only place there are real benefits to cooling the air is when it can get so hot as to promote preignition, or when too much heat builds up, as in diesel engines with turbochargers.

Great! I'm glad it took care of the problem. Let us know if you have questions in the future, and I'm glad it helped you.

Take care,
Joe

Dandy. Be aware these brake light switches have at least two separate switches built into the assembly, and three if it has cruise control. When the switch is just slightly out of adjustment, one of those switches will change before the others, so the cruise control can kick out, and / or the torque converter can unlock, when you do not see the brake lights flash. That makes for a potential misleading clue.

One part of the switch is normally on, and it turns off when the brake pedal is pressed. That one can develop arced or pitted contacts and appear to switch off for just a tiny fraction of a second when driving on rough roads, even when the switch is adjusted properly. The best way to identify that is to use a scanner with record capability. I have a Chrysler DRB3 for all of my vehicles. Among other things related to the cruise control, it lists the "Reason for last cutout". If you're standing still, that will be, "vehicle speed too low", so you have to read this while on a test-drive. If "Brake pedal pressed" pops up while driving, you would know to suspect the brake light switch or its adjustment.

On some vehicles the scanner shows the reason for "Torque converter lock-up denied". That could be due to the engine isn't warmed up yet, or road speed is below 35 mph. If you see "Brake pedal pressed", again, suspect the brake light switch. The computer unlocks the clutch in preparation for it thinks you're preparing to come to a stop. Failure to unlock the lock-up clutch, (a Chrysler invention for better fuel mileage), would snub the engine off exactly the same as if you failed to press the clutch pedal with a manual transmission.

Check and test all the following below:

Oxygen sensor
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)
Dirty or worn spark plugs
Bad plug wires
Weak ignition coil

If a vehicle idles erratically and surges (idle speed is not steady and increases and decreases), the problem may be a buildup of carbon or fuel varnish deposits in the idle speed control valve (also called the idle air control valve or IAC valve). The cure for this condition is to clean the valve with some aerosol throttle cleaner or engine top cleaner

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires