SRA

They have the A240L transmission, more interestingly the overdrive engagement also depends on coolant temperature, TPS position and Throttle cable adjustment.

I've been trying to troubleshoot some issues with my 2000 AE112 since I bought it second hand and it seems that I wasn't checking the TPS correctly, many manuals says to check and adjust using the Idle pin which I have done multiple times but it seems it was correctly set already, while doing that I have noticed that the TPS plug coming from the ECU doesn't even have a wire for the idle PIN, can anyone please let me know whether this is the same case with their AE112s ? and If possible advise what voltage at the signal wire on both closed and WOT. Thanks in advance.

I would try to do everything to prevent that cable from popping out again, using zip ties, … etc, otherwise the next easiest option is to get another cluster, which will come with its own odo KMs. It makes sense that you can't get 4th gear as this is the only gear that is ECU controlled on those cars and the ECU decides when to engage it depending on the speed which is fed from a cluster inductor.

How's the temperature gauge when that happens? Does it point below the middle during high idle? could be a stuck open thermostat or a worn thermostat seal, they are both very easy to replace.

Check for leaks from the spark plugs tubes seals few days later, at that age they are usually brittle and crack from the smallest disturbance during removal of valve cover.

The hunting seems like a bad or out of adjustment TPS, check it. Does it consume coolant or oil excessively, does it blow smoke at the tailpipe? How hot is the radiator outlet hose when it is overheating?

When it comes to things like thermostats my recommendation is to stick to the original, even if you had to buy an aftermarket one to keep the car running that should only be temporarily until you get the original. I believe the Toyota dealer should be able order it for you even if it took sometime to arrive, it won't be longer than other suppliers anyway.

I forgot to add I also checked carefully all vacuum hoses for any leaks but they're all in good condition, engine doesn't consume any oil and coolant is clean and at steady level.

Hello Everyone, I decided to publish this issue after I just replaced many parts ,ran out of ideas and about to give up. Three years ago I've purchased an auto AE112 with 150K on the odometer, shortly after I've noticed that idle would dip below 700 rpm only when in Drive or Reverse, in N or P it just sits at 700 rpm and it's nice and smooth. Additionally the car felt a bit weak on low-end torque and I just think that fuel economy could also be better, however it has been driven or long and short trips and it didn't miss a beat. Starting to troubleshoot that, beside doing normal services, I replaced O2 sensor, PCV valve, thermostat and its gasket (car wouldn't warm up in cold weather), all the parts are genuine Toyota. I also checked and tested parts like Knock sensor, ISV, spark plugs, TPS, O2 output and MAP sensor, Distributor pickups, cam timing, valve clearance and all were fine. I purchased a timing light from a local store and went to check ignition timing, it was set at 2-3 BTDC (with TE1 and E1 jumped) so I changed it to 10 BTDC as the sticker on the engine cover says, the idle issue has almost gone but it pings a lot on that setting so I decided to retard it back to where it was, I've tried 4 BTDC and it would ping slightly for a split of a second when taking off in hot weather so retarded it again to where it came originally. I even doubted the timing light and bought another one of a different brand but they both showed exactly the same thing. The only case when it won't ping on 10 BTDC was using 98 RON but I need to figure out what is wrong with it. I have a feeling that the ECU is not retarding timing as it should but I'm trying to find out why. If anyone can share their thoughts that will be appreciated. Cheers