Idling problem, emergency!

[Yimu]

Sorry to bother you guys again, yesterday i just changed 2 injectors, knocking sensor tps and all the hoses for my 94 Q45, car turned out much quieter but now there is a big problemAfter i crank the engine up, the idle is really high, and it drops to 200rpm later on and suddenly jumps up and stays at 1000rpm, after i start accelerating, sometimes engine suddenly jumps to 2500 rpm and suddenly gets down, cant feel shifting.The tps and some spark plug coils were used, never had this type of problem before, please some one could advice whats the problemReally need the car to workThanx

[Skibane]

My guess: Your (used) TPS is noisy.

As the throttle moves through various positions, a noisy TPS sometimes hits a dead or erratic spot, giving the ECM a false indication of throttle position. So, the ECM sets the engine speed based on what it THINKS the throttle position is, rather than what the throttle position REALLY is.

Could also be a poor connection on the TPS connectors - look for corrosion or a connector that isn't pushed all the way on.

[Yimu]

Yah, thanx for the tip, was the TPS caused the gas and air mixture errorSolved the problemBut another problem came up, the idle speed is still a bit high, 1000rpmhow can i lower thatthanx

[elwesso]

Adjust the IAC.. Turn it al the way in then about 2 turns out.

[sdkhalsa]

Had the same sympoms on 94' Q. Like you I had just replaced the TPS(new unit)) and the idle shifted from normal, 750, to about 1500. Looked all over the place place for a vacuum leak, checking the EGR valve, and even cleaning the IAC valve which looked pretty decent to begin with. As Wes suggested, I took care of the symptoms by closing down the IAC valve, but my feeling is that the idle position had been disrupted with ECU. My understanding is that this idle position position can best be reset with a Consult. Getting ready to try doing this on a Nissan Data Scan program. Please let me know if you have any big breakthroughs.