Hunting/surging at idle

[Daveyboy]

Hey guys,
So I got a Silvia s13 sr20det and it hunts at idle.
The ecu is auto but has had the 5 shift conversion.
When I put in a manual ecu the rev counter doesn?t work and it misfires like a bitch. With the auto ecu it drives fine!
I tested the tps and that?s fine. Took the idle control valve out tested that and cleaned it, both solenoids moved when given 12volts. After putting everything back together clean with new gaskets I tried to adjust the idle control valve.
After unplugging the tps the engines idle went to about 2000 and wouldn?t drop, moving the idcv screw doesn?t make any difference what so ever.
I have order a new tps (just in case) but does anyone have any advice or thoughts??
Thanks!!!

[zombiewolf513]

check for vacuum/boost leaks. the bend brake booster hoses crack a lot.

did you test the tps for resistance (ohms)?

[Daveyboy]

It’s had new hoses recently but yeah I checked again and found a few leaks, inlet gasket and housing coming off the turbo to inlet pipe. No just for voltage.

[zombiewolf513]

Fix the leaks first and check the resistance across the top 2 terminals off the TB. should sweep smoothly between .1 or .2 ohm 'closed' to about 5 ohm when all the way 'open'. Adjust to .45V installed with TB fully closed, should sweep smoothly to 5V at wide open throttle. Heres a vid of a good vs bad TPS:

https://youtu.be/6SR0oIuC0z4

You should also check all your grounds. Have the motor grounded to the frame?

[inopsey]

does the surging correspond to any change in timing at idle. ive seen unstable timing (+/-2 degrees) at idle correspond to hunting at idle. it would be weird for this to be happening with what you described but if the basics (given above) check out and you have access to a light see how stable timing is at idle.

[inopsey]

i may be wrong here but isnt the auto and manual tps different parts? they would need to correspond to the correct ecu to work properly?

[S14rebuild]

i may be wrong here but isnt the auto and manual tps different parts? they would need to correspond to the correct ecu to work properly?


Auto ecu will work on manual, not the otherway around.

Auto tps has 3 of the same wires, other wires are specific for the auto trans. Will work just fine

[Daveyboy]

Good morning guys,
I live in Okinawa so that’s why there may be some late replies!
Today I will check the resistance of the tps and make sure the body is well grounded! (I know the engine is as I took a big ground off which is attached the the inlet.
This s13 has cam and crank sensors which I would assume if the timing was out would throw up a code or atleast a light. The engine doesn’t seem to miss, it’s a definite hunt/surge. Iv got a good diagnostic machine on the way so I can get some live data on it (assuming it can correspond with the s13 ecu) I also thought last night if there was a o2 sensor playing up that would throw the air/fuel mix off and cause it to hunt. I’ll see if I can find what the resistance should be for them and check them today!
Thanks for the input guys, any more thoughts are more than welcome!

[Daveyboy]

Fix the leaks first and check the resistance across the top 2 terminals off the TB. should sweep smoothly between .1 or .2 ohm 'closed' to about 5 ohm when all the way 'open'. Adjust to .45V installed with TB fully closed, should sweep smoothly to 5V at wide open throttle.

I checked the resistance of the tps on 20k Ohm setting (only one I could get it to register on) the plug has 6 pins and with the clip facing away from you bottom far left with top middle pin it red 1.67 (closed) and 11.13 (fully opened).
It sweeps smoothly though does this seem high?
I fixed a broken earth going to the o2 sensor but that made no change, I wonder if the o2 sensor is faulty? I can see the ground wire to the engine block is corroded so I?ll order that and change it when it comes.

[inopsey]

i want to understand your car better. is it a real silvia/180? (i see your in Japan) was it originally an auto s13?

[Daveyboy]

It’s a Auto to manual conversion sr20det. There was a broken wire to a o2 sensor I fixed to no change. Was wondering if there was a bad ambient air temp sensor somewhere which may have been throwing the fuel air mixture off. Tested the coolant temp sensor yesterday and tested okay. What puzzles me is how the idle control valve screw changes nothing to the idle when adjusted in or out..
any thoughts?

[Daveyboy]

It’s a Silvia sr200det s13. Originally auto now manual.
It’s now just misfiring the hunting problem has been fixed. Ordered a probe to check the timing is right and a set of coils and igniter. Also ordered compression test and fuel pressure tester. I can help but feel the injectors might just need a good cleaning though!
I’ll get to the bottom of this one way or another!
Any other suggestions are more than welcome other wise I’ll post when I manage to find the problem.