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Car dies after adjusting throttle cable

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geosok

Proven Member
116
6
Jan 12, 2017
Las Vegas, Nevada
Hello all, I created a new problem for myself after fixing what I thought was an issue. Got done doing a full check up on my car after a new head gasket install (compression, BLT, plugs, etc...) and after logging in ecmlink I noticed my throttle was stuck at 4% open. Ironically it was idling perfectly and I told my self not to touch it but I couldn't help myslef.

I adjusted the throttle cable on my 99 GSX, got a new log showing 0% open and retweaked the TPSVolts to .63

Now the new problem is the car won't stay running. If I lift off the pedal it sputters at 200 rpms and then dies, if I control the idle with the pedal it runs great with no other issues. Is there a setting on the ecu I'm missing or have I adjusted the cable incorrectly?

Thanks in advance as always.
 
The throttle isn't supposed to be fully closed. It needs to be slightly open so you're not choking out the engine and also so it doesn't stick. The only exception to this is when there are hole drilled in the butterfly plates like on carburetors
 
usually there is a passage in the throttle body that goes from one side of the plate to the other.
this is the path that allows air into the engine with the throttle completely closed.
the idle air control motor blocks part of the passage.
the IAC moves to increase or decrease the amount of air thru the passage.


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if your IAC isn't working or you have block it off, then you need to keep the throttle plate slightly open to idle.
if you want to check your IAC, you need a multimeter. you should have around 30 ohms between the middle pin and either of the outer pins.
here is a pic
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(click for full size)



this is from the ecmtuning wiki

Throttle-body problems​

The simplest path through the throttle body is the Basic Idle Speed Screw (BISS). This screw controls an otherwise fixed air bleed that allows air to bypass the throttle plate. Screwing the BISS in reduces the amount of air that reaches the intake manifold, screwing the BISS out increases the flow. If the only problem is that the BISS needs to be adjusted, simply adjust the BISS until the ISCPosition value logged in DSMLink/ECMLink hovers around 30 at normal warm-engine idle in neutral. This produces better results than following the service-manual procedure.
You may find that screwing the BISS all the way in doesn't bring the idle speed down to idle speed configured in DSMLink/ECMLink. That means that some other path is allowing too much air to pass. First make sure that there is no leakage into the BISS hole by covering the hole with your finger. If the engine speed drops when you cover the hole, replace the BISS O-ring.
Next, investigate possible problems with the Idle Speed Control (ISC) servo. Open the ECU and inspect for burned ISC driver chips. If you find any, contact ECMTuning regarding repair of the ECU. If there are burned drivers, it's quite possible that the damage was caused by ISC itself having a shorted coil. Make sure you are using the correct O-ring to seal the ISC to the throttle body. An O-ring that's too thin might not seal, too thick and it might not allow the ISC to fully close the airway.
Test the coils in the ISC. (Note that the newer, more reliable, all-black ISCs normally measure about 39 ohms.) Inspect the tip of the ISC for any physical damage.
Test for proper operation of the ISC: Turn off the ignition and reset the ECU by removing battery backup power for at least 10 seconds, then restoring battery backup. Then, with the ISC unbolted from the throttle body but plugged in to the wiring harness, turn on the ignition and observe the movement of the ISC. The ISC should fully extend, then retract slightly. If the ISC just quivers a bit but doesn't really move, suspect a problem with the ISC, the driver circuits in the ECU, or the wiring. If the ISC fully retracts instead of fully extending, there is a wiring problem, perhaps a mismatch between '90 and '91+ engine harness and ISC. Using a '90 harness with a '91+ ISC, or vice versa, will cause the ISC to operate backwards.
Strange behavior can result from a bad Fast-Idle Air Valve. This is a coolant-temperature controlled air valve that provides some of the additional air needed for fast idle during engine warm-up. This valve is integral to the throttle body, so test by substitution or by blocking the FIAV passage with a block-off plate.
With all other possibilities eliminated, the remaining item to check is the throttle plate. A too-tight throttle cable can pull the thottle open, more so as the throttle-cable housing heats up, so make sure that the throttle cable has sufficient slack to allow the throttle to close to the stop even when the engine is hot. Check that the throttle is against the stop by manually rotating the throttle shaft closed. Make sure that nothing is binding the throttle shaft such as bad bearings or a badly adjusted throttle-position sensor.

Other considerations​

In order for the ECU to attempt to control idle speed at all requires that the ECU know that the throttle is closed. The ECU knows this by the state of the idle switch, so make sure that the idle switch is working by logging IdleSw in DSMLink/ECMLink or use DSMLink/ECMLink to simulate the operation of the idle switch. Idle surge results from the ECU being forced to limit idle speed by shutting off the injectors until the engine speed drops low enough. When the ECU re-enables the injectors, the engine speed jumps back up.
Ignition timing also has some effect on idle speed. In fact, the ECU normally varies ignition timing at idle to provide fine control over the idle speed. Make sure that base ignition timing is set properly.
If you are running a configured idle speed that's higher than stock, it's possible to observe a slight oscillation in idle speed even when everything else is working properly. This is because, by default, the timing tables in the ECU significantly advance ignition timing as the engine speed rises above 750 rpm, and engine speed tends to increase as ignition timing is advanced. You'll want to reduce this positive feedback by retarding the ignition timing at idle and slightly above idle. It also helps by giving the ECU's fine idle control mechanism more authority.
Also, as your idle speed setting is increased, the intended idle speed begins to get pretty close to the rpm at which the ECU cuts fuel when the idle switch is active. A good rule of thumb is to set the Coasting FC Offset to your rpm setting minus 900. For example, if your intended idle speed is 1100 rpm, set the Coasting FC Offset to 200 to raise the fuel-cut threshold by 200 rpm. Doing so also helps ensure that the idle switch will deactivate before the engine speed increases to the coasting fuel-cut threshold during no-load throttle application.

idlesurge.txt · Last modified: 2016/01/12 18:41 by nickracer
 
Last edited:
Viewing live data my car is at 2.8% at idle without touching the throttle and 5% in my WRX

thats why most tuning software has an option to zero out the TPS.
and if your running a modified jeep 60mm TB, they like to stick so you wouldn't want it to close tight, but pretty close to it.
 
Thanks everyone for all the help, I appreciate it very much. I'm off to undo my mistake from yesterday, hopefully I won't decide to touch anything else, LOL. THANKS AGAIN!
 
The throttle isn't supposed to be fully closed. It needs to be slightly open so you're not choking out the engine and also so it doesn't stick.

No, the butterfly is meant to close fully (But not bite into the bore). The Idle stop screw on a 2G or the IPS on a 1G do that. There are three idle bypasses, the BISS, the ISC, and the FIAV that provide air needed.

The TPS has specific adjustment specification depending on 1G or 2G and what it reads also depends on the generation. 1G's read 10% when the TPS is correctly adjusted and a 2G should read 0% because the voltage can vary and the ECU scales the reported value.
 
So I adjusted my throttle cable and had a similar problem on mine but where it would idle really low and die when cold. Found the problem was that whoever owned the car before me had put an aftermarket bov on and stuck a filter over the recirc tube. Don’t know why I didn’t think of that sooner, but a leak behind your maf could maybe be the problem. Just something to check.
 
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