4AGE jumpy at constant speed/LIGHT throttle cruising.

[ManicVJ]

Hi all,

Have an imported JDM AE86 with the standard, early version 3rib Bluetop Bigport TVIS stock as far as I know.

Currently while driving between 1500-3200rpm on LIGHT throttle (around town cruising usually, sitting on 50/60km/h) The engine seems to kick a bit, hard to explain but while holding minimal throttle to cruise at 50/60 it seems to buck back and forth, like i'm constantly moving the throttle back and forth quickly+slightly. Sort of like it's cutting fuel slightly or missing? Not quite sure.

If above 3200rpm no sign of the problem, runs great, very smooth right through to redline and pulls well. Idles perfectly and throttle response is even better after adjusting TPS. Seems to only be at LIGHT throttle the problem occurs.

I have read up on the subject and so far have readjusted my TPS, have also disassembled and thoroughly cleaned my throttle body as well.

Have tried leaving the TPS unplugged, does the same thing while cruising. Although when pulling up will not idle, just rough idle/shake and die without it plugged in.

Have so far found a few things to try:
o2 Sensor
Spark Plugs
MAF Sensor
Vacuum Leaks
EGR Valve

Was just seeing if anyone else has had the issue? Maybe could steer me in the right direction cheers all. ;)

[Matt]

Was going to suggest adjusting the TPS, but you did it already. Did you use the guide here?


https://www.youtube.com/watch?v=k7jS1y70S98

I'd also check the timing is right, i.e. make sure it is set in the diagnostic mode with the pins bridged. It's almost like you are labouring the engine too much and just need to shift down a gear?

[axalotyl]

... while holding minimal throttle to cruise at 50/60 it seems to buck back and forth

The AE86 always was a bit touchy at very low throttle openings.
Doesn't like the engine pulling down to low revs while in gear... gets
a bit of "bucking" going on, and can be quite violent. You have to
de-clutch quickly, and take a lower gear. I believe that at very small
throttle openings the ECU reads the TPS as being closed, and initiates
fuel cut. The slightest touch of the throttle brings the fuel back on
and this sets up "driveline snatch", which is very similar to chain
snatch on a motorbike.

Fuel cut occurs with closed throttle above approx 1700 rpm and left
alone, the fuel comes back on when the engine revs drop to around
1300-1400 rpm. If this is the bucking you are referring to, the best
cure is just to drive around it, by always taking a lower gear when
driving slow or coasting up to the lights. Go down through the gears
rather than letting the car slow right down to an idle in 4th.

Cheers... jondee86

[ManicVJ]

Hi again all, sorry about the late reply.

After cleaning the injectors, throttle body, changing the plugs, checking the timing, replacing fuel filter, adjusting TPS...

All these things made slight improvement after each one.

O2 sensor was the culprit, have picked up a brand new NTK sensor (which included the correct plug!) all has been fine since.

Think it was a good thing I have gone though what I have as the 4A-GE has never been happier! Cheers for the help.

[Matt]

Weird, I've ran without 02 sensors a few times without any issues

[Javal]

Weird, I've ran without 02 sensors a few times without any issues

In some instances, no reading > false reading.

[ManicVJ]

Absolutely!! Unplugging the sensor was the first time it ran along at 50/60km/h without issue.

Bought the new one the next day.

[Matt]

Either way that is good info to know.