Hello fellow car enthusiasts, long-time reader here seeking some expert advice. I’m facing a perplexing issue with my trusty 1994 Toyota Previa SC, which has served me faithfully for 215,000 miles. Recently, after a short 30-mile drive, it started exhibiting a really rough idle and performance took a nosedive. It feels exactly like an ignition problem, but I’m starting to suspect something deeper, possibly related to a bad idle air control valve. At idle, the engine nearly stalls, and hitting the gas results in frustrating bogging. It’s like it’s starved of air or fuel, or maybe running excessively rich. Nursing it home at a snail’s pace was the only way to get back.
It’s been sitting idle for about two months since then. Today, I decided to tackle some routine maintenance hoping for a quick fix. I replaced the spark plugs (with Autolite APP-3923, gapped at .043 and torqued to 20ft-lbs), distributor cap and ignition rotor, fuel filter, and air filter. I even added fresh gas. Unfortunately, none of these changes made any difference to the rough idle issue. I was initially hopeful because the old spark plugs were the incorrect type for the supercharged engine (NGK BKR5EP-11) and had been in use for approximately 30,000 miles. Plus, the old rotor and cap did look a bit worn. I opted not to replace the spark plug wires as they are relatively new, with less than 20,000 miles on them. Perhaps this was a mistake?
One thing I noticed is that the engine seemed to run reasonably well until it reached operating temperature. The missing and hesitation started right around the time the transmission was shifting into overdrive. This makes me wonder if it’s temperature-related or perhaps linked to engine load once warmed up.
The check engine light is illuminated, which should provide some diagnostic data. My Previa has what appears to be an OBD2 port near the fuse box, but also the older diagnostic port under the passenger seat. I’m unsure if it’s truly OBD2 compliant, as the under-hood sticker doesn’t explicitly mention it. I attempted to retrieve trouble codes by jumpering the TE1 and E1 terminals in the diagnostic port, but the only response was the oil light blinking every 6 seconds (transmission in neutral, key in the ‘on’ position). My OBD2 scanner is arriving this Saturday, so I plan to try reading codes from the OBD2 port then, just to be sure. My intuition points towards a sensor issue, or maybe those spark plug cables after all, but my gut feelings haven’t been reliable lately! Could a bad idle air control valve be the culprit? Is there a way to get OBD2 love data from this older system to help diagnose this bad idle?
If anyone has insights on what I should investigate next, please share your thoughts. I need to figure out if this repair will be budget-friendly. If I can resolve this current engine problem, my next projects are rebuilding the SAD shaft and replacing all four struts/shocks. But, I can’t move forward with those until I conquer this rough idle issue. Bringing my Previa back to its former glory is my goal, as it’s always been a dependable and robust vehicle. I genuinely love this van and want to keep it running for a few more years.
