Vtbbs2k

I have only reset the ecu one time and that was about 4000 miles ago when I cleaned the iacv I do not keep resetting it. The problem is still there, the reset as far as I can tell did not help nor hurt and has not changed as I have driven over the past couple months

JulieU

IDK if this would help, but curious if you put it through a proper idle learn procedure whenever you reset the ECU.

Vtbbs2k

yes I did that after ecu was reset did not help any

vtec9

I would start trouble shooting the individual sensors and components.. perhaps a friend will lend you a map sensor

blasphemy101

Curious what you find. I've been having the same issue for quite some time now.

I've tried:

Coil packs,
Injectors,
IACV,
MAP Sensor,
Cleaning Throttle Body,
Valve Adjustment

Next on my list to look into are the primary O2 sensor, IAT, and CLT. I plan to get an OBD2 reader to try and see what kind of readings the sensors are producing.

Vtbbs2k

Hey blasphemy I'm assuming you replaced the map and iacv ? Have you you checked you're tps yet? I was thinking of possibly checking the primary o2 also.
This is such a pain in the ass problem I've had it for quite some time too

gptoyz

Hey couple of diagnosis methods you can try as well.

I'm assuming the IACV operates such that when their is no power or off, the valve is shut (no air/less air). Try unplugging your IAC valve's electrical harness and starting the car, the car if it starts should idle higher (choking the engine of air)

Another suggestion start the car and let it warm, then tap the iac valve body with the butt of a screwdriver if the idle fluctuates when you smack it the motor is probably sticking or bad.

blasphemy101

I tried cleaning my IACV first, but it didn't help, so I picked up a used IACV and swapped it out; the problem remained consistent, so I'm ruling the IACV out.

I replaced the MAP sensor with a new one straight out of the box, and there was no change, so I returned it. I did the same thing with the coil pack I tested.

No, I haven't checked the TPS voltage yet. According to the FSM, the car should operate in closed loop idle using just the primary O2 sensor to determine the required fuel output, so the MAP, IAT, CLT, and TP sensors shouldn't have much of an effect on it. The TPS may be the culprit if it's giving a false reading and keeping the ECU from going into closed-loop. I had this problem on a car I was tuning not too long ago. A bad speed sensor MIGHT cause a similar problem, if the ECU looks at it to enter closed-loop idle.

The crank sensor is also another possible culprit, since it tells the ECU what RPM the engine is really turning.


Yes, unplugging the IACV should cause the idle to shoot up and start bouncing.

gptoyz, I found your video on YouTube, and your issue is exactly like mine. I take it you haven't been able to resolve it yet?

gptoyz

Hmm I don't think I posted a video of this problem, did I? But it's my friends car that I have been troubleshooting.

Hmm have you checked all the vacuum lines. One thing with buying a used iacv is how do you know it's not bad as well?

And speed sensor, hmm I would think if the speed sensor detected movement it would move away from an idle map.

As far as crank sensor, is their anyway to see the value through obd2?


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blasphemy101

This isn't you? https://www.youtube.com/watch?v=OUWiVJJxmp0

The youtube user name is the same as your name on here; that's why I was thinking it could be you. The problem in this video is identical to mine, except my problem goes away when I turn the headlights on (the high-beam light is on in the video).

I don't know for a fact that the new-to-me IACV is good, but the problem didn't change, and all other signs point to both my original and the new-to-me IACV being good. Even if the new valve was bad, I'd expect some kind of change in the problem. It is exactly the same.

Like I said, the speed sensor COULD cause the ECU to stay out of closed-loop idle, but quick reading through the FSM didn't indicate one way or the other. If the speed sensor is involved, I wonder how the ECU is meant to handle situations where the car is coasting in neutral...

Again, from very brief reading in the FSM, it looks like the engine speed indicated through the OBD interface is pulled from the crank sensor. I would expect the case to be the same for the value on the tachometer, but the FSM recommends comparing it to the tach, so that might not be the case. The FSM states the engine speed should be 800 +/- 50 RPM at idle.