|
Sorry to drag on about the throttle body, but I just had to convince myself that wasn't it.
If the IAC is your current suspect then when the idle is high try pinching off the hose going to the IAC. Use either special soft-jawed hose pliers made for this job or simply pad a pair of pliers with a rag so as not to damage or split the hose. If the revs are high due to some other problem and the IAC is operating normally then the revs should drop maybe 100-200 rpm at most as the ECU would already have been trying to keep the IAC closed. If the revs drop down much further, hopefully to about 450 rpm and possibly stalling the engine, then you know that the IAC is either stuck open or not able to be controlled. If you take the IAC out, when you give it a quick twist by hand the piston should be heard/felt to open and the spring should immediately return it to the rest position (there should be about a 1/4" visible slot opening when at rest). You can also try to open the piston valve fully (the opposite way from the at rest opening) using something non-marring like wood coffee sticks and when released it should quickly return.
Your 1990 B230FT should have the LH2.4 system with an OBD (aka OBD-I) diagnostic socket on the left strut tower brace. There are a number of things you can do with OBD-I to help narrow down your problem:
o Try putting the engine in "limp home" mode by turning the ignition off and disconnecting the AMM. Restart -it should then run in limp home mode where it should be able to idle (although poor) and be driveable up to about 2000 rpm (although rough). If the engine can now idle at or below 1000 rpm then you know it's likely an input control signal, such as from the AMM, ECT (engine coolant sensor) or oxygen sensor, that is causing the problem. The ECT sensor is very much associated with idle speed and any jump in rpm could mean a loose or shorting ECT wire (be careful to locate the ECT not the water temp sensor for the dash gauge). There are also cases where the ECT and knock sensor connectors can get interchanged and this will cause operational problems (I can't remember the exact symptoms).
With OBD you can do additional testing and also exercise some of the fuel system components. The test at function 3 will be of most interest to you at the moment:
o Function 1 is to check for any stored trouble codes (see FAQ). This should be done whenever there are engine problems even if the Check Engine light hasn't come on. Check both the fuel system (socket #2) and the ignition system (socket #6). To enter function 1: turn ignition on (car not running); put OBD selector wire in socket #2 or #6; press button once (hold button 1-3 seconds each time when pressing); the LED should start flashing Morse-type codes. A code of 1-1-1 means no more codes. Each time you press the button the next code will be read. Continue pressing the button until you get 1-1-1 or the first code is seen again. Check the FAQ for details on the individual codes. Reset the codes by holding the button for 5-10 seconds until the LED lights then release and press again for another 5 seconds.
o Function 2 is to check some of the inputs. To enter function 2: turn the A/C off (and out of defrost position); turn ignition on (car not running); put OBD selector wire in socket #2 (fuel system); press button twice (hold button 1-3 seconds each time when pressing); the LED should start flashing:
a) Watch the LED; open the throttle fully and hold; when the TPS goes click you should get a code of 3-3-2 (it says 3-3-1 in the book, but I got 3-3-2) then WOT throttle has been properly detected. Now close the throttle; when the TPS goes click you should get a code of 3-3-1 (says 3-3-2 in the book, but I got 3-3-1). You can continue to repeat this test opening and closing the throttle fully. If you can't get these codes and the LED just keeps flashing when you open or close the throttle then the TPS signals aren't getting through to the ECU, either a faulty TPS (presuming it is properly set to go click) or a wiring problem.
b) Now start the engine. The LED should stop flashing and you should get code 3-3-1. If you don't get that code or the LED continues to flash then the signal from the rpm sensor on top of the bell housing behind the block isn't getting to the ECU, either a faulty or weak rmp sensor or a wiring problem.
c) Switch on the A/C. The LED should stop flashing and you should immediately get code 1-1-4. When the compressor kicks in you should get code 1-3-4. If you don't get those codes or the LED continues to flash then the signal from the A/C compressor isn't getting to the ECU, typically a wiring problem. Switch off A/C.
d) For automatic transmisions only, hold brake pedal down; place in Drive then return to Neutral. You should then get code 1-2-4. If not then the transmission shifter switch signal isn't getting to the ECU, typically a broken switch or wiring problem.
o Function 3 is to exercise some of the engine outputs. To enter function 3: turn the A/C off (and out of defrost position); turn ignition on (car not running); put OBD selector wire in socket #2 (fuel system); press button three times (hold button 1-3 seconds each time when pressing); LED should start flashing: While it is flashing the OBD system will continually cycle through some tests:
a) You will hear the injectors being opened and closed. Put your hand on each one to feel the clicking.
b) You will then hear the IAC (idle air control valve under the intake manifold) being fully opened and closed. Put your hand on it to feel a solid thunk at the end of travel. I like to let function 3 cycle through a number of times as forcing full travel of the IAC may actually improve a sticky valve.
c) If present, you will then hear the solenoid valve (at left front fender) being opened and closed.
d) If present, you will then hear the cold start valve being opened and closed.
--
Dave -not to be confused with a real expert, just goofing around at this
|
