This '88GT has 40k miles, and after many years stored in the sun I'm trying to recover it. The engine/trans are now fine, the fuel tank/sender/filters are all correct, the interior is superb, and 100 small jobs have been completed.
It just got new struts and shocks, as well as urethane bushings in the rear, and then was aligned on an excellent system by a competent tech. Driving at a steady 70mph, it tracks well, steering wheel is centered, and it feels good.
HOWEVER When the throttle is opened the car swerves slightly to the RIGHT. When the throttle is closed, it swerves slightly to the LEFT. It seems that even after all that suspension work, torque affects the steering.
A common problem with the '88 rear knuckles is that the bolt hole for the lower lateral links can wear out of round and allow the knuckle to "steer" with throttle and braking.
Grab the wheel at the 3 and 9 o'clock positions and wiggle it vigorously while a helper watches this area closely for any movement of the bolt relative to the knuckle. If there is play, then that's the likely source of your problem.
You can solve the problem but it will cost a bit of money. The unworn hole measures 12 mm in diameter so you can upsize to a 1/2" bolt but this requires the knuckle to be bored out very precisely by a good machine shop. Then, you also have to bore out or replace your bushing sleeves to match the larger diameter bolt.
If it isn't a loose knuckle then it may just need an alignment. I once lowered my rear suspension (coil overs) and didn't align it right away. It did exactly what you described. Pulled to one side under power and then pulled to the opposite side when lifted the gas pedal. A worn knuckle will cause the alignment to shift, but if the knuckle is tight is might be a rear toe condition
I put it on the rack this morning and inspected. Everything seems to be ok, and the black-painted links with red poly creates an impressive look.
Exercising the wheels did not produce evidence of a distorted hole in the knuckle on either side. With 40k miles I would not have expected serious wear there, and am thankful the problem lies elsewhere.
It's probably alignment, though it was expensively done yesterday. The shop had the best equipment, but I have doubts about the human factor. I'm not sure my "1988 is different from all other Fieros" was considered. I called the manager, who agreed to revisit the issue.
Can anyone connect me to the correct data for aligning an '88GT? Torque steering is often attributed to toe-in errors, so I'm particularly interested in those numbers.
i have the same issue with my 88 at times, ive had the alignment checked several times now, and ive had the knuckles off and checked the holes 2x each now, i do have noisy strut mounts tho, im ordering new struts monday and going to change the struts and mounts.
For those of you who also stumble onto this post, and your long knuckle bolt is really tight:
Make sure the axles are torqued to spec through the bearings. When I did my swap, I setup the cradle out of the car, and although I got the axle nuts as tight as I could with the cradle/suspension out of the car, it was nowhere near the 200 ft. lbs. needed and I had the same problem as the OP until I remembered.