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The engine is idling +/- 850 RPM. Target idle is stock programming = 800 RPM. As I suspected, IAC counts are “0”. That means the PCM saw the idle was too high and started closing the IAC down to lower the idle. Once it reached 0 counts it can’t close any more. MAP is relatively healthy (33-34 kPa), not necessarily indicating a vacuum leak.
Best way to set up the log is start the engine cold, let it warm up without touching the accel pedal, etc. Here's a copy and paste of my data logging guide:
DATA LOG GUIDELINES
Do not reset PCM. Do not remove a battery cable. Do not pull the PCM BAT fuse.
Start COLD engine. Do NOT turn on A/C or Defrost. Turn off traction control (ASR / TCS) if vehicle equipped.
Leave the accel pedal alone. Do NOT rev the engine while it is warming up. Don't drive it. Leave it alone.
Allow engine to idle for at least 4 minutes. Should be long enough to warm up and put PCM in closed loop.
Start driving car for about 5-10 minutes. Vary the accel pedal position and RPM. Make at least one WOT pull from a roll up to at least 5,000 RPM.
Mentally note (or have a passenger write down)when the engine exhibited the problem you are chasing.
Stop driving, let it idle for about 30 seconds, without touching the accel pedal.
Finished.
Don’t do the 5,000 RPM pull.
I'll look at your current log tomorrow in more detail, on a PC where it's easier to manipulate Excel than on my iPad.
Your closed throttle position voltage is a bit high. Stock, unmolested value is usually around 0.65 volts. Yours is 0.78 volts. Suggests someone might have moved the throttle stop screw to open the blades up a bit at idle. With the engine warmed up, idling try slowly backing the throttle stop screw counterclockwise and watch the idle RPM. See if it comes down.
The throttle stop screw is accessed from the rear of the throttle body. In this photo of the back of the throttle body, the stop screw is in the hole with the blue circle. As I recall the screw is a Torx head.
Yes it can be accessed with the throttle body in place.
With the engine fully warmed up note the idle speed. It would logically be in the range shown in your data log, 850+ RPM. If you can observe the RPM using Scan9495, it will be more accurate than the tachometer. Isn't unusual for the tach to read 100-200 RPM higher than actual RPM. With Scan9495 you could also note the throttle position sensor voltage. In the log it ranged from 0.78 - 0.80 volts.
Just turn the screw counter-clockwise 1/2 turn. See if the stop lever moves to close the blades. Wait 30 seconds, and check the RPM again, and the throttle position voltage.
If the blades moved and the RPM dropped, note the TPS volts. Continue adjusting the screw until Scan9495 shows 800 RPM. Typically the RPM will move +/-25 RPM as the engine idles, but you want the average to be 800 RPM. If the IAC counts are shown, they should have moved above “0”.
If this doesn’t lower the idle speed, you will know that something other than the throttle body that is causing the problem.
I can’t fit my t 10 in there since my throttle cable bracket blocks it. Could a exhuast header leak being causing this problem? Fully warmed up it seems like it likes 900 rpm and will stay at 1200 rpm when pulling up to a stop sign.
Hopefully you understand why the idle speed does not drop down immediately to 800 RPM when coming to a stop. I tried to explain that in post #44, but apparently that wasn’t too clear. If the car is moving (MPH not equal to 0) the PCM keeps the IAC open until the car comes to a full stop.
The data log shows the long term fuel trims on Bank #1 as very high, indicating the PCM is adding as much as 15% extra fuel because it thinks there is a lean condition. A leaking exhaust before the O2 sensor can cause a “false” lean condition. But it's too much air that controls the idle speed, not the fuel.
As far as accessing the stop screw, you might need a 1/4” ratchet or flex handle, a flex joint, and a 1/4” Torx10 male socket. I don’t remember having a problem accessing it, and have those tools. I can’t go out and take a look because I sold the car almost 2 years ago.
[EDIT] I looked in my tool box. I have a set af right angle “Allen” keys with Torx heads. That should make it easier.
You have to follow my instructions if you want my help. See post #46 for data log guidelines. From a COLD START, and I added: Don’t do the 5,000 RPM pull.
11-20-2023 | 07:39 PM
