I was recently faced with a poor running sports car from the late seventies. The vehicle had been in storage for a long time and it took a fair bit of work just to get it running. Once running again on clean fresh fuel and cleaned fuel injectors (the rubber hose portions of the fuel system had rotted internally and plugged up the injectors) the performance was less than spectacular.
Full throttle performance was acceptable but part throttle cruising and acceleration was jerky. Time to check the basics. Everything was set to original specifications but at idle and cruising the vehicle was running lean, too much air and not enough fuel. Something had to be done.
The seventies had brought us emission controls. Up to that point in time vehicles were tuned slightly rich (a little extra fuel makes a vehicle run smoother as well as producing a little extra power). Slightly rich tuning will tolerate wear and tear and imbalances between one cylinder and the other. Reduced emissions and high fuel economy demands ushered in fuel systems that could be run closer to the edge of lean and maintain cylinder to cylinder balance.
Many of these vehicles did not age gracefully. Wear and tear would sway lean a little too lean.
A little too lean meant poor performance. Surging and jerky transitions while cruising were the result.
Most of the time these vehicles exhibited these problems later in their lives (long past warranty) and in many cases the manufacturer was no longer helping with a fix. The repair was up to the your local mechanic.
To maintain emissions compliance the systems were locked in a seventies fashion. Any adjustments that could make lean a little richer required more than a screwdriver or a wrench to adjust. The choke adjustment was riveted in place. The idle mixture screw was hidden behind a pressed in cap.
A chisel, a hammer, a drill and a thorough understanding of performance tuning and your mechanic could have your vehicle performing perfectly. Emissions compliant? Maybe not, but good driveability.
Usher in the twenty first century’s computer controlled vehicle systems. These vehicles run for years, in many cases flawlessly. Computer control systems with feedback keep the edge of lean on the edge.
Even so some of these systems exhibit flaws. For emissions compliance purposes these vehicles are locked from any adjustments. The locks are now cryptographic (google it).
As before you can find a mechanic with a computer, some software, some read/write hardware and a thorough understanding of performance tuning who can make that flaw disappear. Emissions compliant? Maybe, maybe not, but excellent driveability.
Performance tuning lives on.
Back to that seventies sports car. After a little research (thank you google) the solution is clear. The air flow sensor (a flap that measures airflow into the engine) can be adjusted. The cover is glued on to prevent tampering. An exacto knife removes the cover. Once inside, a plastic gear can be adjusted to release the spring tension on the flap. Less tension, more flap movement with any given airflow. More movement, more fuel.
Just what the doctor ordered.