I'm not exaclty sure how bad fuel can cause fuel pressure to be higher than normal. Are they saying it could be due to excess gunk in the fuel filter from bad fuel? Have you experienced poorer fuel economy? It's quite easy to check the air filter, spark plugs and fuel filter yourself, but if you are not confident in doing so, you can take it back to Toyota; I'm not sure how happy they would be at taking directions from you (after all, they are supposed to be the ones doing the troubleshooting right?) and they may charge you for it. Perhaps you can say that performance still seems sluggish after running 98 for the last 3 tanks as they suggested. Ask them for more info about what steps they did to troubleshoot the problem last time. Ask them if the throttle body was dirty enough for them to clean it, did they inspect the air filter too? have you driven on some very dusty roads? Ask them if they thought the bad fuel was so bad that would cause a rise in fuel pressure, did they check if the fuel filter was clogged? and whether they checked your spark plugs were fouled. They were probably too lazy to check the fuel filter as I believe it requires removal of the rear passenger seat (haven't actually performed this task myself yet), they will also most likely tell you that the fuel filter doesn't need to be replaced till 80,000km or something like that. In anycase, if they say that the batch of fuel was so bad that it caused a rise in fuel pressure, they should at least inspect the fuel filter. In modern cars, the ECU controls everything, even down to the opening of the throttle (electronic throttle, as opposed to a cable in older cars). When you step on the accelerator, you aren't actually opening the throttle directly, you are triggering a switch that sends signals to activate the throttle electronically. Anyway, as modern engine management systems control everything, a reset of the ECU can at times help with restoring performance: especially in situations where say the breathing of the engine has been improved, or you had an especially bad batch of fuel and the ECU had retarded ignition timing etc. The ECU will usually take time to adjust back to optimal settings; resetting the ECU in this situation will speed up this process.