My girlfriend has a 1995 240sx SE. KA24DE w/5 speed. Approx 125k miles.
I started doing some work on her car due to her car stalling out when the gas was let off. She had to "strategically shift" as I call it, and have to downshift to at least 2nd, engine brake to 1k rpm's before depressing the clutch. It was a major pain the a**, so I pulled the intake manifold and replaced all the vacuum lines, thoroughly cleaned everything that had carbon and oil residue, and replaced all the gaskets I came across.
Now it's back together and there seems to be (at least) 2 new problems:
It all starts with the resting idle of the car. It won't go lower than 1000 rpms even with the idle screw turned all the way in. I checked the impedance of the IACV and it checked out, as well as the continuity on all the wires up to the main connector in front of the intake manifold. Opening the IACV valve brings the engine up to around 1500. The next thing I checked was the TPS. Again, impedance is within listed limits. If it's turned all the way to one direction to get the lowest impedance at closed throttle (1.4k ohms) and has a smooth increase up to 10.3kohms at full throttle. Having the TPS affects the idle initially, raising it to around 2k rpm's at start up and then it lowers to 1k. The other thing that happens with the TPS plugged in is an afterburn on deceleration. It only happens when the TPS sensor is plugged in; unplug it and the car returns to idle without pops from the exhaust. So... high idle, and after burn. Help?
I've been workin on this for the past couple weeks following diagnosis instructions in the FSM and I'm starting to get a little frustrated. If anyone has some insight on what may be the issue, I'd love to hear it.
A little background on what else has been done in the past:
- TPS replaced less than a year ago
- MAF replaced less than a year ago
- Disty, cap, and rotor replaced less than a year ago
- I recently changed the oil pan gasket, belts, removed the marbles from the tin can (timing belt guides), and put in fresh oil and coolant.
Advice Needed for Idle Issue
Re: Advice Needed for Idle Issue
I'm dealing with a similar problem on a 93 S-13, 5-sp swap. Idle stays around 1000-1200 even if the idle air adjusting screw is turned clockwise all the way in. When you are turning the screw, it is on the Idle Air Adjusting (I.A.A) Unit. Just above the I.A.A is the Idle Air Control Valve (IACV)-Air Regulator. This regulator provides an air by-pass when the engine is cold for a fast idle during warm-up. There is a heater and rotary valve built into the air regulator. When the temp is low, the air by-pass port opens. As the engine starts and electric current flows through a heater, the shutter turns to close the by-pass port.
My guess is that your air regulator is bad or stuck open, always providing bypass air thus making the ECU run high idle. So, even if you turn the adjusting screw all the way in, the air regulator is still providing more air, thus high idle. The FSM has a test that starts on page EF&EC-141 (for 91-94) then goes to pg 167 to diagnose the air regulator. The resistance of the air regulator should be approx 75ohms, but it could also be clogged.
When the car is idling, if you unplug the E.F.I sub-harness connector (located at front of intake manifold and to the left of the TPS) the idle should drop to 700 ish. The ECU is no longer getting signals from the IACV valve and will revert to stored idle of a car that is not cold.
I was checking for vacuum leaks as a potential high idle problem and in the process of replacing the hose that feeds bypass air to the air regulator (second smallest hose leading from air intake and connects to a metal tube that runs back to the air regulator) when the car was running, I unhooked the hose at the air duct assy. plastic connector and the car started to stumble and die, but then I plugged the hose with my finger, and it idled fine.
The air regulator is held on by two 10mm bolts, the top bolt is easy, the bottom I'm not really sure how you get it off, very hard to access. I'm thinking you need a 1/4" drive 10mm socket (that has a thin wall) so it can access the bolt. I have another air regulator, but have to get the old one off to test my theory.
My guess is that your air regulator is bad or stuck open, always providing bypass air thus making the ECU run high idle. So, even if you turn the adjusting screw all the way in, the air regulator is still providing more air, thus high idle. The FSM has a test that starts on page EF&EC-141 (for 91-94) then goes to pg 167 to diagnose the air regulator. The resistance of the air regulator should be approx 75ohms, but it could also be clogged.
When the car is idling, if you unplug the E.F.I sub-harness connector (located at front of intake manifold and to the left of the TPS) the idle should drop to 700 ish. The ECU is no longer getting signals from the IACV valve and will revert to stored idle of a car that is not cold.
I was checking for vacuum leaks as a potential high idle problem and in the process of replacing the hose that feeds bypass air to the air regulator (second smallest hose leading from air intake and connects to a metal tube that runs back to the air regulator) when the car was running, I unhooked the hose at the air duct assy. plastic connector and the car started to stumble and die, but then I plugged the hose with my finger, and it idled fine.
The air regulator is held on by two 10mm bolts, the top bolt is easy, the bottom I'm not really sure how you get it off, very hard to access. I'm thinking you need a 1/4" drive 10mm socket (that has a thin wall) so it can access the bolt. I have another air regulator, but have to get the old one off to test my theory.