Intermittent stalling
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4th Gear Member
Joined: Nov 2006
Posts: 1,229
From:
Intermittent stalling
Hey guys, this is starting to get annoying and flat out dangerous, so I think it's time to address it. My car (2000 GT 5 speed) will stall once every 2 months or so randomly. It did it backing out of my driveway, while on the highway, while coming to a stop off an exit ramp and while in gear in traffic (didn't stall obviously but bogged like it lost fuel for a second or 2). The car is basically stock, it's got a BBK CAI, C & L upper intake elbow, and 75mm BBK TB; that's all the mods I can think of that might cause this.
The car seems to do it when I hit the brakes with the clutch in (apart from the one time in gear when I was in traffic), thats the only thing I can think of. Is there some sensor on the brake booster or something that's supposed to raise idle when the brakes are applied to prevent this?
Could my IAC be going bad? Maybe a bad ground somewhere for the fuel pump or something? Crank sensor going bad? The crank pulley does have oil on it, so maybe the crank sensor has some on it and is losing the reading sometimes? The car does seem to idle at different RPM's sometimes; sometimes as low as 500, but normally its 7-800.
Fuel pump and filter were replaced April of 2010 so maybe the ground is loose?
Did I answer my own question? Help haha
The car seems to do it when I hit the brakes with the clutch in (apart from the one time in gear when I was in traffic), thats the only thing I can think of. Is there some sensor on the brake booster or something that's supposed to raise idle when the brakes are applied to prevent this?
Could my IAC be going bad? Maybe a bad ground somewhere for the fuel pump or something? Crank sensor going bad? The crank pulley does have oil on it, so maybe the crank sensor has some on it and is losing the reading sometimes? The car does seem to idle at different RPM's sometimes; sometimes as low as 500, but normally its 7-800.
Fuel pump and filter were replaced April of 2010 so maybe the ground is loose?
Did I answer my own question? Help haha
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
The only feedback to the PCM regarding engine load is from the AC system, there are no other sensor or switch inputs to the PCM for that purpose. To handle the other vaiablt load peripherals the PCM monitors engine speed and constantly modifies the duty-cycle of the IAC drive signal to open or close the IAC as needed.
Here's what this signal looks like at idle.
99.44% of all idle issues are caused by stuck/sticking IAC valves, you can quickly test it by disconnecting the electrical connector while the engine is idling and hot. The idle speed should drop immediately, and perhaps stall--if it does not the IAC is bad, or there is a wiring problem.
Test the voltage at the connector, between the red wire and ground, with the key on and engine off (KOEO)--it should be 10.5V or more, typically 12.6V to 13.2V.
If it is then check the solenoid coil's resistance across the IAC's input terminals--it should be 6.0Ω to 13.0Ω, if not the IAC is bad;
If the coil's resistance is within range check the resistance between each terminal and ground--both should be >10kΩ, if not the IAC is bad;
If the IAC checks out test the throttle position sensor (TPS).
In KOEO mode monitor the voltage, between the gray/white wire at the TPS and ground, while slowly opening the throttle--it should rise smoothly from 0.6V to 1.0V, up to 4.5V to 4.9V, as you open the throttle. If the voltage range is not observed, or if the voltage reading is erratic and jumpy, then the TPS is bad.
Here's what this signal looks like at idle.
99.44% of all idle issues are caused by stuck/sticking IAC valves, you can quickly test it by disconnecting the electrical connector while the engine is idling and hot. The idle speed should drop immediately, and perhaps stall--if it does not the IAC is bad, or there is a wiring problem.
Test the voltage at the connector, between the red wire and ground, with the key on and engine off (KOEO)--it should be 10.5V or more, typically 12.6V to 13.2V.
If it is then check the solenoid coil's resistance across the IAC's input terminals--it should be 6.0Ω to 13.0Ω, if not the IAC is bad;
If the coil's resistance is within range check the resistance between each terminal and ground--both should be >10kΩ, if not the IAC is bad;
If the IAC checks out test the throttle position sensor (TPS).
In KOEO mode monitor the voltage, between the gray/white wire at the TPS and ground, while slowly opening the throttle--it should rise smoothly from 0.6V to 1.0V, up to 4.5V to 4.9V, as you open the throttle. If the voltage range is not observed, or if the voltage reading is erratic and jumpy, then the TPS is bad.
Thread Starter
4th Gear Member
Joined: Nov 2006
Posts: 1,229
From:
Well let me start as always saying thanks Cliffy; I really do appreciate you alwaya typing out the long helpful responses. I tested everything and everything tests out perfect just as it should. Course I had to play with something while I was there... TPS was at .8 so I adjusted it to .94 hehe
Anyway, any other ideas?
Anyway, any other ideas?
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
Well let me start as always saying thanks Cliffy; I really do appreciate you alwaya typing out the long helpful responses. I tested everything and everything tests out perfect just as it should. Course I had to play with something while I was there... TPS was at .8 so I adjusted it to .94 hehe
Anyway, any other ideas?
Anyway, any other ideas?
The EECV PCM monitors the TPS voltage continuously while the engine is running, and records the lowest observed voltage as being closed throttle, this is called a "ratch" (reverse latch) value, and is used as the basis for any throttle position calculations. Since the TPS' angular resistance rate is known, and a fixed 5.0V reference is applied, it is a simple thing to determine the throttle blade position when the current voltage and the ratch voltage are known.
From the shop manual:
Idle Speed Control Closed Throttle Determination
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start. This lowest learned value is called "ratch," since the software acts like a one-way ratch.
The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.
All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode.
An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start. This lowest learned value is called "ratch," since the software acts like a one-way ratch.
The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.
All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode.
An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum
Thread Starter
4th Gear Member
Joined: Nov 2006
Posts: 1,229
From:
Adjusted the TB and reset the KAM. The car definitely seems to idle better and have more control of where it idles at. I guess only time will tell if I truly fixed the problem, but I get a good feeling. Thanks again Cliffy!
TECH SAVANT
Joined: Dec 2006
Posts: 10,937
From: Saint Augustine, FL
Give it a while, it should relearn the idle air trims and settle in...
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