Thanks for all the great info and the pic. Here's a few tidbits (my own War and Peace) from my own recent experiences with my 95SC4. I notified my local Lexus dealer of the hesitation issues. He suggested a very expensive 60K tune up and fluid replacement service, and to add a throttle body assembly cleaning. The tech who worked on it has been a Lexus tech at this dealership since 1992. He said that the SC4's engine was indeed redesigned for the 96 and later models. He explained why the service for 92-95 models is MUCH more expensive than for the later models. It's because, when servicing the older units like mine, Lexus REQUIRES the valve covers to be removed and valve clearances to be checked and reset to factory tolerances. For the 96+ SC4 engines, the shims and their mounts were redesigned to be more consistent long term (maybe the ECU/EGR were, too?). So the techs only 'listen' to the covered valves when servicing the 96 &+ models, and will then remove the valve covers to service the valve/cam assembly ONLY if they hear an audible ticking. This saves an hour or two of labor plus the cost of the valve cover gasket(s) for 60K services on the newer models. Upon completion of this service, I experienced some improvement to the hesitation issue on my car. But it's still there, still noticibly after the engine warms up in warm outdoor temperatures. So the service did not eliminate the issue. The tech then stated (as you were told) that this hesitation issue is a problem common to this engine (thanks, great timing). He did not say if it was true for all years 92-95, or just the 95's. But he came as close to admitting a design flaw as he could without outwardly dissing his company's product. I thought this was the same engine as that installed in the LS400s of the day (if anyone knows differently, plz let me know). I cannot imagine how a design flaw of this magnitude across both models could not have been documented as a service bulletin at Lexus, not to mention corrected in a recall.
Other comments from the tech on this model which are not related to hesitation, but might be worth sharing:
On occasion, owners of this car may encounter a 'burnt' smell when operating the vehicle. He explained this is odor from the sprayed on underbody treatment being seared by the extreme heat from the catalytic converter. Could this heat also fry the underbody mounted O2 sensors eventually? Although the same tech told me it's unlikely (since his diagnostic showed my O2 sensors are 'ok'), I may yet try replacing them. Although the sensors may not have failed enough to trigger a diagnostic code, they could possibly be impaired and be sending erroneous data to the ECU, which in turn could contribute to its poor control of the EGR. I'll then reset the ECU, and keep my fingers crossed.
Items known to be failure points on this car: rack and pinion steering, undersized brake pads which require frequent replacement (always use expensive factory pads to avoid squealing)
Items that are robust and tend not to fail: A/C, Tranny, Engine overall supposedly good to 200-300K
