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Discussion Starter · #1 ·
My RPMS are floating between 1k-2.3k RPM's when in neutral. Sometimes they just dip up and down with a consistent rhythm, and several times they have just got stuck at 2k.

I don't know much about cars, I'm learning as things break on mine. I changed my plugs and wires about 3k miles ago. I'm assuming it's either a misfire or a transmission problem.

Any guesses/suggestions?

5,550 Posts
You either have air getting in to the intake after the VAF or try this …

You need the following tools over and above usual spanners/sockets and alike.

1. set of feeler gauges (including .006"(.15mm) & .020"(.50mm))

2. Timing lamp

3. multimeter (volts and ohms)

4. 2.5mm Allen key wrench

1. Make sure you have the proper amount of coolant (8 quarts) in your system.

Start the car, let it warm up, and have the radiator caps loosened. Once the small overflow reservoir fills up, cap it. Watch the filler neck by the pass. Side of the engine, squeeze the hoses and burp all bubbles out of the system. Try to just keep the water level up in the neck so it can't suck air back in, and be careful the stuff gets hot! Squeeze the hose till the fluid is all the way to the top (ready to spill out) and cap it tightly. Once you're content all air bubbles are out, move onto the next step.

Q. Why worry about coolant?
A. Bubbles in the IAC are bad and make idle fluctuate in a slow, annoying way.

2. Set the timing

Insert a jumper pin between the TEN and GND pins.

Hook up the timing light to the battery for power and hook up the signal to the #1 wire location marked on the distributor cap.

Loosen the two 12 mm bolts on the disty so it can rotate (not too loose).

Now, with the jumper pin inserted, start the car, if it dies, open the idle air screw on the top of the throttle body a couple turns.

Q. Idle air screw?
A. If you don’t know the idle air screw is shown in the picture below.

Make sure the car is warmed up, NO accessories or fans or anything is on, and if the idle is like 1500 then close the idle air screw a little, it should be open 2-3 full turns.

Now, move the power steering hoses and wires out of the way, point the flashing timing light at the crank pulley, and watch the small tab on it illuminate and reference it's location to the small timing marks on the plastic tab that sticks out over it.

Q.I can’t see it A. It can be a bit trying but it is there look down from left to right @ the main drive pulley

Rotate the ditsy until the notch on the crank pulley is exactly in line with the "10" on the plastic timing mark indicator (this is 10 degrees before top dead center).

Now adjust the idle air screw until your idle sits right at 650 rpms.

Check the timing mark again, adjust if required and reset the idle air screw to 650rpm (depending on how far out your settings are you may have to do this yet again)

Now when it's at 10 deg., and the revs are 650 +or- tighten the disty down carefully so as not to move it. Turn off the car, remove the jumper pin.

Throttle and tps setting..

Now, take your voltmeter. Set it to ohms. Touch the two terminals on the idle air bypass control valve.

Q. what/ware is the bypass valve?
A. black cylindrical “thing” on bottom of throttle body)

The resistance should be 10.2-12.3 ohms. If so, then that is ok. If not replace.

NB: You may skip the bypass valve step and only check it if you still have problems after setting every thing else, as it is in a tricky spot requiring removal of air intake box for good access..

With the keys turned to off unplug the TPS.

With the voltmeter still on ohms (or continuity check mode), touch the two lowest pins with the terminals of the voltmeter. There should be continuity. If not, loosen the two screws holding it to the throttle body so you can just rotate it, and rotate until you get continuity. Now retighten.

Make sure that the stop screw that the linkage hits JUST barely touches it at closed throttle.(2.5mm Allen key wrench for it).

You will need some feeler gauges. (Q. what’s a feeler gauge? A. a set of metal strips made to specific widths used for setting gaps)

Next, take a .006"(.15mm) feeler gauge, and put it between the throttle stop screw and the throttle linkage (back/top of the TB).

Now with the .006" feeler gauge inserted, there should still be continuity, if not, rotate the TPS until there is.

Once you have achieved this remove the .006” and switch to a .020"(.50mm) feeler gauge.

Now there should not be continuity, if there is continuity redo the previous step until it is correct.

Plug the sensor back in, use the paper clip to jump the TEN and GND pins. Turn the key to the on position (don’t start just ignition/red lights)

Now take your voltmeter, and put the black lead on the neg. terminal of the battery, and tap into the yellow wire on the TPS (2nd wire down from top of TPS harness). I use a sewing pin and just push it into the wire.

The Voltage should be between .1 and 1.1 at closed throttle,

At wide open throttle it should be 3.6-4 volts (check by pressing gas pedal to ensure it opens fully). If these values are within these specs you are all set, if not replace the TPS

Now start the car, your idle will be perfect. :tup:

1,050 Posts
Mr. MX6 real nice write up!

2,602 Posts
nice write up but $10 says he just has a vacuum leak somewhere

5,550 Posts
like i said first guess is air getting in after vaf...
and yea i wrote that yrs ago..
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