What is the problem with a Geo Storm when it tries to stall when idling at a red light andor when the same car wants to stall when you try to back it up in the parking lot?

Answer 1

Isuzu engines commonly exhibit erratic idle problems

The engine revving and dropping in rpms, sometimes dropping almost to the point of dying. There are several things that can cause this problem:Leaks in the vacuum hoses or aged, cracked hoses can let in air that is not being metered by the ECU's sensors.Leaking or sticking EGR Bypass valve may be allowing exhaust gasses into the intake when the engine is not under load (idling). Loose electrical connections in the engine sensors can cause problems.On G200, 4ZC1, and 4ZD1 Engines: The Idle Control Valve / Idle Solenoid may not be functioning properly.On 4XC1, 4XE1, and 4XF1 Engines: These engines are notorious for idle speed revving and dropping. Thus far, no single simple answer has been successful in all situations has been offered.Before you do anything at all, check the ignition timing and reset it to factory specifications (9-11 degrees). Incorrectly adjusted ignition timing (too far advanced timing), will cause havoc within the ECU and the engine will not idle correctly.After this, the first step would be to carefully remove the IAC control valve and clean it with carburetor cleaner, xylene, or some other solvent and a tooth brush.Also clean the passages in the throttle body, and then reinstall the IAC valve, making sure to reinstall the O ring also. This may resolve the problem in some very mild cases.Check the throttle cable adjustment. If the throttle cable is adjusted too tight, the throttle position sensor will not read that the throttle is closed at idle, and this will cause the computer to fight to lower the idle speed. Make sure there is some slack in the line and that the throttle arm easily and consistently rests against the throttle adjustment screw whenever there is no pressure on the pedal. If it does not, then examine, repair, or replace the throttle cable and gas pedal if anything is found in either of these assemblies to show the cable or pedal is sticking.

If this does not help, things get much more complicated. These engines are set up with a learning mode and the computer controls all functions, including idle speed, based on the signals from the sensors. If one sensor begins to malfunction but does not go totally dead, the computer will continually try to adjust, causing all sorts of symptoms, and even running the trouble codes will not help, because it will show nothing unless the sensor is dead.The best and easiest solution is to have a service department use a scan tool to determine the problem. Anything else would be a futile effort to guess and get lucky on what the problem is and pray that you don't waste hundreds of dollars replacing sensors that are not defective.The throttle position sensor on these vehicles can not be adjusted. This does not mean that the sensor can not be twisted on its mounting bolts so that the baseline voltage reading is different, it means that the baseline voltage reading is meaningless, and the computer takes whatever the lowest voltage reading sensed to be 0%, no matter what that voltage may be. Using the scan tool and observing the physical position of the throttle linkage at the throttle body, observe that the percentage reading does not always return to 0 though the linkage has physically returned to its fully closed position. This appears to be a voltage variance in the sensor signal from the ECU. The voltage sent to the sensor from the ECU increases above idle speed above the 5 volts specified, and though the linkage and sensor return to the fully closed position, the increased voltage in the sensor signal causes an increas3 in the voltage returned by the sensor, so the ECU does not believe the throttle plate is fully closed, and tries to continually adjust the ignition timing and fuel injectors to for a condition it can't determine is idle or above idle.

If you insist upon this hunt-and pray method, your possibilities are: coolant temperature sensor, mass air pressure sensor, intake air temperature sensor (thermistor), oxygen sensor (exhaust), etc. You should disconnect the battery for several minutes after making any changes to clear the learning portion of the computer memory, this way, if you are lucky enough to guess which sensor is bad and replace it, the computer will not continue to try to compensate for the bad sensor that it sensed before.If you decide to take the vehicle to a service department to have it scanned, make sure that they have and can operate a Delco Tech I tool and have the software to service your vehicle. Know that these Delco computers (ECU or CPU as they may call it) are flash programmed. They do not have a static programmed prom chip, and rather are "flash programmed" by loading with the software from the Tech I while the computer is installed in the car. They do have learning modes, do have a memory, and are programmable. You will find that many dealer service departments have little or no experience working on anything other than trucks and sport utility vehicles. They may have no experience in dealing with the Delco based computer controls on these vehicles, and may even make claims that these computers are not programmable, etc. Make sure that you quiz the people who you intend to have service your vehicle. If they are not familiar with the Delco based computers, claim anything other than that they are fully programmable and flash programmed using a Tech I, or indicate that they lack the hardware and software to service your vehicle, do yourself a favor and take your vehicle somewhere else to someone who has at least the slightest idea of what they are doing.Also note, that there have been numerous recalls on the Delco ECUs used in the Isuzu and Storm models which are listed at the website. Specifically, all 1991 Isuzu cars have a standing recall # 9101001 under General Recalls for a ECM replacement campaign, and all 1990-91 Geo Storms have a standing recall # 91C066E under Emissions Recalls for ECM replacement because of emissions non-compliance. It appears that the computers should be recalled, and that a recall was issued by Isuzu, but that this recall is no longer being honored by the company. If this is the case with your vehicle, changing all the sensors will have no effect, and only by replacing the ECU will you ever solve the problem.

Lastly, to improve drivability without fixing the problem so that you can use the car despite its idle problem, if you find that the vehicle is revving and dropping and trying to die, you may wish to try one of the following temporary cures:If you live in a climate with little temperature variation and it is always 70 degrees Fahrenheit or above, you may wish to start the engine, allow it to warm up, wait for the engine to idle at a normal speed, and then simply un plug the IAC solenoid. This disables the IAC solenoid and the computer will not be able to continually try to correct for whatever problem it has that is serious enough to warrant correction, but not serious enough to bring up a trouble code when the codes are run. Disconnecting the IAC solenoid will, however, make it almost impossible to use the air conditioning, as the IAC solenoid usually adjusts the idle speed up to compensate for the increased drag of the compressor. Disabling the IAC solenoid eliminates this, and the engine will die if you turn on the air conditioning. This will also happen if the temperature drops enough, and engine warm up will become difficult. Adjusting the throttle plate stop on the throttle body is the second possible action, which works much better if you are in a climate where the temperature is not steady and cooler whether is normal. Note that the throttle stop is set at the factory, there are no instructions to return the throttle stop to its original position, and if you have the vehicle serviced by a dealership service department, their instructions are to replace your throttle body ($400.00 or more) if the adjustment screw has been tampered with. That said, you can adjust the idle screw in several threads to artificially raise the minimum idle speed. The computer will still try to compensate, but will not be allowed to let the engine speed drop low enough to kill the engine. The side effect will be that once the engine gets hot, the idle speed will hover between 2,000 and 3,000 RPM often when you pull to a stop at a stop light or stop sign. Sometimes it will work its way down after several minutes, and sometimes it will simply hover at that point. It is annoying, but much less so than having to continually restart the engine every time you come to a stop. This temporary solution should not be used in the long term. It is not good for the engine to run above idle for long periods with no load. In addition, it is not good for the life of the clutch to start from a standing stop at 2,000-3,000 RPM all the time.