Rb20DET High Idle fix

[Jermaine7430]

I don't know if this has been covered before but I have seen the high idle problem many times in forums. I have a 92 240sx with Rb20det swap. Car was wired horribly first of all, I fixed the wiring and drove the car for while when I found that the car stalled on decel. I fixed this by replacing the spring in the IACV. This fixed the stalling problem but created the high idle problem. I stumbled upon the fix of this problem which was to simply adjust the TPS by sound. You will notice that the idle will drop and may idle up and down, but all you need to do now is adjust the idle screw on the IACV using a timing light or your gauge to read the rpm. Adjust to about 800 or more to idle smoothly, the book says to use the idle screw on the computer but that does not work very well. As long as all your vacuum hoses are good this will solve the problem.

[Gabes13]

The signal voltage is affected when adjust the tps that way. That can alter fast idle contacts and arf ratios. You have to make sure the tps is set to 0.45v +/- 0.05v and then adjust with the idle screw on the iacv.

[Jermaine7430]

That is true but the problem is the tps reacts like the throttle is stuck open when the thermostat opens, water contacts the coolant sensor which controls the iacv through warmup. It is suppose to rely on the operation of the O2 sensor when the throttle is pressed, or when warmup is complete so an adjustment was needed. The typical voltage is .45 but that is where the problem is. The rb swap requires an other than ordinary adjustment because you will not have all the helpers that the skyline car has to assist its engine. I have also noticed that the system operates at a high voltage all the time that is resulting in overcharging of the battery. This affects the iacv because as the car heats up the voltage is suppose to drop, this is not happening as it should.

[Jermaine7430]

My Tps is set at .48 which is slightly higher but the tps now responds like the throttle is closed, which it should.

[Sily20DET]

Very interested in this subject as i am havin so many dramas i have a s13 with a rb20det, im getin ecu codes sayin my tps and engine temp so there obviosly stuffed coz i ran my own wires for both to the ecu, no change. Soon as i rev it itll come back down and stall sooo frustrating. Ive non stop searched since i bought it done and checked everythin thanks to the posts on this site but still the same. Ye forgot ive also got high idle the spring in the air reg under the T/B i cut the spring a tad shorter so it fully closed the little plate thing and still the same and ill disconnect my tps and adjust my idle screw then reconect but my idle will not go bellow 1400 rpm Will the o2 sensor really affect idle/driveability much? Coz mine aint connected still tryin to find a new 1 without payin auto barn $220 for a fekn o2 sensor all i can say is lol

[Jermaine7430]

The 90-95 model 300zx o2 works on the Rb motor and 98 240sx coolent temperture sensor will also work. The O2 sensor being unplugged will cause the idle at higher tempertures to fluctuate, however once the engine is at operating temperture the timing is what keeps you going.

A short spring, if the iacv works, will give you a high idle, or if it is too weak. A spring from a small pin works good. Make sure all vacuum lines are tight and unblocked.

[Sily20DET]

Awsome thanks very much for that info really needed it what would be the go with a second o2 on my cat? Its confusing as someones cut it n the connections r just hangin thinkin of connectin them n see what happens haha thanks again appreciate it