Throttle Linkage Bushings/Adjustment/Micro-Switch Adjustments

1990 XJ-S Coupe (US Spec, 5.3L V12)

 

Tools/Parts:

5/16” Box/Socket Wrench

Magnet Wand

Two Throttle Linkage Bushings (Part Number C34388)

¼” Wrench

Gumout Cleaner

Feeler Gauges (0.002” and 2mm)

Flathead Screwdriver

 

One of the Throttle Linkage Bushings on my ’90 Coupe was disintegrating, and the other one was totally gone.  The bushings on my ’91 Coupe were showing signs of falling apart.  As stated in “Experience In A Book”, this is typical of the rubber bushings.

 

Throttle Linkage Bushing – Left Side                                     Throttle Linkage Bushing – Right Side

 

 

 

 

I followed David Littlefield’s procedure described in the “Book” – use a 5/16” wrench to loosen the “pinch bolt” as shown in the photo below and leverage the loosened arm forward as far as it will go.  Remove the “Spring Clip” (using a magnet wand to keep it from falling into the darkness).  You can then slide the butterfly shaft (also known as the “connecting rod”) rearward (to the right in the photos) enough to get the ball end of the shaft out of the throttle assembly, then move the shaft forward and slide it out…

 

Throttle Linkage Bushing Removal

(Left Side)

 

   

 

 

I got my replacement bushings from Motorcarsltd.com (their part number IN101300) for $0.40 each (two required).  Using a bench grinder, carefully remove the beveled lip, and then place it on the rod.  Put the rod back, replace the spring clip, slide the pinch bolt lever towards the rear and tighten the pinch bolt.

 

Throttle Linkage Adjustment

Once you change the bushings, you really should (must) adjust the linkage so that both Throttle Butterflies open at the same exact time.  According to the “Book”, it requires five adjustments (I’m pretty much plagiarizing from the “Book” below – skipping all the typical banter found therein), however I add three more adjustments for some of the “Micro-Switches” that are directly affected by Throttle Linkage Adjustment…

 

Before doing this adjustment, you might want to check/adjust the Throttle Potentiometer (not mentioned as part of Linkage Adjustment in the “Book”).  If potentiometer needs replacement or adjustment, you’ll need to remove/reinstall the Throttle Pedestal, which can have an effect on the Throttle Linkage adjustment.

 

First, remove the Air Filter Housing outer covers and Filters – if the butterflies and throttle throats need cleaning, do it now with some Gumout or the like.  Disconnect the Throttle Rods from the Throttle Pulley (pulling them off the ball joints).  Loosen the Pinch Bolts that you just tightened above.  Loosen the Butterfly Stop Screws (by loosening the locknuts first – see photo below).  While holding the butterfly closed, move the Pinch Bolt Lever down at least one click (the shaft is splined) to make sure this part of linkage is not preventing the butterflies from closing.

 

1.     Centering Butterflies.  Loosen the two screws holding the Throttle Butterfly to the shaft.  Close the butterfly all the way and retighten the screws.  This supposedly centers the butterfly in the opening.

 

Throttle Butterfly Centering/Stop

(Looking into Air Filter Housing)

 

 

2.     Butterfly Stop Screws Adjustment.  The stop screws are adjusted so that the butterflies nearly completely close, but not quite to prevent jamming.  Insert a 0.002” Feeler Gauge at the bottom of the butterfly as shown, hold the butterfly closed and adjust the Stop Screw until the butterfly “just starts to let go” of the Feeler Gauge (kind of like using a Feeler Gauge on a Spark Plug).  It may take a few times to get the feel of it – just make sure that both sides are adjusted to the same feel.  Re-tighten the Stop Screw lock nuts.

 

Throttle Linkage Adjustments

(Left Side)

 

 

3.     Butterfly Shaft Lever Stop Adjustment.  The front side of the Butterfly Shaft has “Lever” (for lack of a better term) that hits a solid stop underneath the Butterfly Stop Screw.  Hold the butterfly closed.  Move the Butterfly Shaft until that Lever hits its stop, and then move the Pinch Bolt Lever until there is as little “backlash” (looseness) as possible.  Tighten the Pinch Bolt.

 

4.     Throttle Crossrods Adjustment.  Put the Throttle Crossrods back on.  Put a 2mm (0.079”) gauge between the Throttle Pulley and its stop (see photo).  Loosen the locknuts on both ends of both Throttle Crossrods and turn the crossrods until the butterfly just starts to open (using the 0.002” Feeler Gauge in the Butterfly will help).  Re-tighten the crossrod locknuts.

 

Throttle Crossrod and Full Throttle Stop Adjustments

(Viewed from Left Side)

 

 

Recheck the adjustments so far.  Put the 0.002” Feeler Gauge back in the butterfly and turn the Throttle Pulley (without touching the crossrods) until the Feeler Gauge “falls out” – they should open at the same time.  The gap between the Throttle Pulley and its stop should be between 0.062”-0.094” when nothing is being touched.

 

5.     Full Throttle Stop Adjustment.  Loosen the Full Throttle Stop locknut and screw (photo above).  Hold the Throttle Pulley in full open position.  Tighten the Stop screw until it just touches the Pulley and retighten the locknut.

 

Now for the other adjustments that need to be done…

 

6.     Idle Micro-Switch Adjustment.  The Idle Micro-switch is on the left side Throttle Linkage (see photo above in adjustment number 2).  Loosen the Idle Micro-switch Adjustment Locknut and Screw and let the Throttle Pulley rest at idle position.  Adjust the screw until you hear the micro-switch click when you start to turn the Throttle Pulley.  Retighten the locknut.

 

7.     EFI Micro-Switch Adjustment.  The EFI Micro-Switch (see photo above) “tells” the ECU if the engine should be in Open or Closed “Loop” mode.  You will see that the Throttle Pulley has a rider that is supposed to engage this switch about ½ way through its travel.  Make sure it does – if not, loosen the tiny bolts on the switch and move the switch until it does.  Retighten the tiny bolts.

 

8.     Kick Down Micro-Switch Adjustment.  The “Kick Down Switch” is meant to force the transmission to kick down to a lower gear when the accelerator is literally floored all the way – all the way.  This micro-switch is mounted next to the throttle cable where the cable is mounted to the Throttle Pedestal.  If you grab the cable housing with your hand and give it a good push toward the pedestal, you’ll see that the cable housing will move and hopefully the roller will engage the micro-switch.  If the switch does not click, adjust it using the two small bolts that hold the switch to its mount.

 

 

Now, open the driver’s side door and put your foot on the gas (with the car off).  Floor it as hard as you can.  Did the switch engage?  Mine didn’t on my ’90 Coupe.  You could adjust the Full Throttle Stop screw a little to see if that does the trick, but since you just adjusted that where it needs to be, I wouldn’t recommend it.  You could try adjusting the Cable Adjustment Nuts, but that resulted in pulling the throttle open a little when nothing is being touched – no good.  In looking under the accelerator pedal, I found a “stop” screwed into the floor, which prevented the pedal from going further down – (I didn’t find a reference to that in the “Book”).

 

 

 

I unscrewed the stop and used a bench grinder to grind down its “lip”.  Put it back in and now the switch engages when it is supposed to.

 

 

Note: After you’ve done the Throttle Linkage Adjustments, you will most likely need to readjust the warm idle speed since the butterfly stop screws have been moved.

 

While your there, you might want to change your Throttle Return Springs.  Next project…