Like many car enthusiasts, I’ve been chasing down a frustrating performance issue in my VR4. It’s a head-scratcher because it seems to resolve itself temporarily, only to return and dampen the driving experience. Let me break down what’s been happening and what I suspect, hoping someone out there has seen something similar.
Initially, I was trying to fine-tune my air-fuel ratio using an AFC-2 to achieve optimal performance – aiming for zero knock and around .94 O2 readings. After dialing in the settings, the car would run incredibly well, but this peak performance was fleeting, lasting only a couple of weeks at best. Soon enough, the dreaded knock would return, showing up in datalogs as high as the low 20s, and O2 levels would dip to .92 or even lower. The perplexing part is that my AFC-2 settings remained untouched. To compensate, I’ve had to incrementally richen the air-fuel mixture every few weeks, which is far from ideal and certainly not easy on the wallet, especially with current fuel prices.
I’ve gone through a series of diagnostics, ruling out many potential causes, leading me to consider an electrical gremlin might be at play. Interestingly, a clue emerged when I was working on my car’s interior. To prevent battery drain while the doors and trunk were open for extended periods, I disconnected the battery. This, of course, reset the ECU. The result? The car felt revitalized, performing better than it had in a long time. Despite the previous knock issues, I hadn’t adjusted the AFC since my last attempt to fix the problem, mostly just accepting a decrease in throttle response. Curiosity got the better of me, and I took a local car club member for a drive, including a few wide-open throttle runs in first and second gear. The car pulled stronger than it had been, with no hesitation. It was like a different machine.
Fast forward two weeks, and the familiar sluggishness is back. The hesitation during wide-open throttle in second gear and beyond has returned, and the overall driving feel is diminished. This pattern points towards either the AFC-2 itself being faulty (though it seems less likely) or, more concerningly, the ECU. I’m hesitant to blame leaky capacitors in the ECU, as the symptoms I’m experiencing don’t quite align with the typical capacitor failure issues reported by others.
Has anyone else encountered a similar situation where resetting the ECU provides a temporary performance boost, only for the car to degrade again within weeks? Any insights or shared experiences would be greatly appreciated as I try to pinpoint the root cause of this frustrating issue.
