Smooth out the idle on a ZX2...

Do you have the dreaded jackhammer idle and steering wheel shake when you are waiting at a red light?

No worries - it’s a common trait among zx2’s but there are ways to improve and fix the idle so it becomes a non-issue. There are things that go wrong on the zx2 that causes this, and there are upgrades/fixes that help too.

Starting with making sure your zx2 is not broken, here are a few possible issues that may cause the bad idle… I am not going to cover things like bad plug wires and spark plugs, because they will show up in other ways besides a bad idle.

STEP 1… Mechanical repairs:

  1. Got codes? If your dashboard SES light is on, run your codes and see if any of them are idle speed related. You may have the answer before going any further in your quest.

  2. Idle Air Control Valve - this lil guy is on the under side of the intake manifold, below the throttle body. It has an electrical plug running to it and is held onto the manifold with 2 bolts. You can check to see if its working by unplugging the electrical connector while the car is idling. If the idle speed drops then it’s most likely doing its job correctly. Mechanics are usually quick to jump on this part and hastily call it faulty.

  3. PCV valve and hose - the pcv valve is in a rubber grommet on the front of the motor just to the left of the water manifold that holds the thermostat. there is a hose that runs from it to the intake manifold and if it clogs it will affect idle. To check it, pull the pcv valve from its grommet, and with the motor running put your finger over the valve orifice. If you get a strong suction from the intake manifold and the idle speed drops, then the hose and valve are not clogged. It’s time to look at #3.

  4. Dirt in the throttle body. residue and buildup can occur around the throttle body butterfly so it’s a good idea to remove the intake tube and with a t shirt wet with soapy water wipe out the bore of the throttle body and wipe clean the edges of the throttle butterfly. A small amount of buildup there can make a difference. You can use a carb cleaner too to clean it, but if you do, make sure its designed for use on coated throttle bodies. Straight carb spray in most cases will attack the plastic coat on the throttle body butterfly and bore.

  5. While your at it, clean out the intake tubes, check your air filter, and wipe all dirt out of the filter housing. Probably not going to help now, but it will prevent problems in the future.

  6. Old worn motor mounts. Just like grandma’s breasts, gravity takes its toll and the constant pulling of weight and rocking back and forth cause the motor to sag, transmitting more vibration into the chassis. The mount over the timing cover is the largest contributor to this issue, and the one over the trans takes second place. The lower mounts have the opposite effect as long as they have their rubber in there, the idle gets better as they age (but unfortunately so does more wheel hop on tire burnouts or drag launches)

OK, assuming all the above is done…

STEP 2: Post OEM Upgrades

  1. PS pressure idle speed switch. This little guy tells the PCM to raise idle speed when you turn the steering wheel. If you unplug it, it will add about 50-100rpm to what the pcm “thinks” you need. The switch is on the PS pressure line along the firewall below the windshield washer reservoir. Unplug it and leave it that way. It will not throw codes nor cause any other issues.

  2. Throttle body stop “adjustment”. When the throttle body snaps shut, a lever on the side hits against a stop to prevent the butterfly from lodging itself in the bore of the body itself. You can bend the stop tab to crack the throttle body open a little more if done right.
    Here’s what you do: Unplug the idle air control valve wire to make it inoperative. Now with it unplugged, bend the stop tab to make the car idle at 700-800rpm approx. Then shut off the car and reconnect the IAC valve wire plug. This will help a lazy IAC valve to do its job better, and make sure you don’t ever idle too low…

  3. If you still don’t have a good idle, then it might be throttle body modification time. This involves removing the throttle body and drilling a 1.8" hole through the butterfly plate to increase the airflow. If you do this, you’ll need to do step #2 over again but set it for 800-900rpm with the iac valve unplugged.

  4. Underdrive pulley. These guys reduce the accessory strain on the motor at idle so things like the ac compressor engaging doesnt become a jackhammer experience. Install directions for this are elsewhere.

  5. Adjustable Cam Gears (retarding intake timing). Reducing idle speed cylinder pressure reduces vibrations too, so if you move the power band up a little by retarding the timing, the motor will smooth out at idle. Cam gear installs or timing belt timing adjustment s are handled elsewhere.

Now, if you have done all those items above and it STILL idles poorly, sell your car. You’re never gonna be happy with it lol.


. If you still don't have a good idle, then it might be throttle body modification time. This involves removing the throttle body and [b]drilling a 1.8" hole[/b] through the butterfly plate to increase the airflow. If you do this, you'll need to do step #2 over again but set it for 800-900rpm with the iac valve unplugged.

umm i hope its a typo?

haha - yes, 1/8" lol

haha otherwise that would be a massive hole in there hahha

yeah, perhaps i should change the instruction to read " remove throttle plate completely, set idle to 6900rpm using duct tape over the top opening. your performance should improve off the line by a small margin but gas mileage will decrease ".