Car bucks/shakes when lightly pressing gas
 

I recently picked up an '87 RX7 TII, and I am experiencing a few issues. The first and most important is this one.

When I am cruising in gear under light acceleration and let off the gas, the car bucks. Also, when I transition from not pressing on the gas to light pressure on the accelerator, the car jerks.

I am thinking it could be bad trans/motor mounts, however I checked them out today and they do not appear to be cracked or damaged in any way. I tried putting the car in gear with the e-brake set to check engine movement, and the engine moved slightly (maybe a couple of inches side-to-side), but that didn't seem out of the ordinary to me.

I also thought that it could be a driveshaft/differential problem, but everything seems tight back there?

Thanks in advance for any help you can provide!

Check in 2nd gen FAQ for 'setting TPS'. This will get you started in the right direction.

I checked the TPS out today. I hooked up a DVM to the correct leads (green/?, black) and read ohms while manipulating the throttle. I have the plunger style, and I wasn't sure if there was a problem with it or not because at about 1/4 throttle it is maxed out. I did some reading and I believe that it the way it is supposed to work?

Anyway:

Closed throttle= .6 kohm
From 1/4 throttle to WOT = 4.5kohms.

Do those readings seem to be correct, and also should the travel of the TPS plunger max out at roughly 1/4 of WOT position?

Closed should read right at 1000 (1K) ohms.

I will adjust the TPS back to spec. Should the plunger only move only part of throttle movement? On every other car I've had, the TPS was full range. Is the S4 FC's not?

The S4 TPS is narrow range only. The S5 version has both a full range and the narrow range. This is why the resistance value maxes out before WOT.

I find it easiest to set the TPS to 1.0V on terminal "A" (http://howto.globalvicinity.com/gv_w...i=58&co=1&vi=1). Just be sure the engine is fully warmed, and the initial set coupler is jumpered (2-wire green plug by leading coil). The first ensures the thermowax has softened and allowed the throttle to rest against its stop, and the second prevents the ECU from changing BAC air while you adjust.