Symptom- truck (1986.5 Hardbody pick-up truck 4-cylinder with electro injection- Z24i engine) hesitates/bucks briefly on acceleration, then runs fine. After finally figuring out how to use the diagnosis feature on the ECM I found the problem was, according to my Haynes manual, in the "Throttle Position Sensor Circuit" (Code 42 on the #40 model ECM in my 24zi). Note that this ECM has "44" as the all OK code, not "55" as in some other models. I replaced the throttle position sensor (~$100, but very easy to replace!) and now the problem really seems to be resolved. Yee-haw.
References:
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To read the ECM codes-1.) make sure module is in "off" mode
2.) turn ignition to on (all dash ligths come on)
3.) turn module to "on" mode (switch on back of ECM)- the ECM is under the passenger seat
4.) the red and green LEDS come on together indicating the ECM is happy
5.) start the car
6.) read the codes (each red LED flash = 10 and each green LED flash=1) so four red flashes and 4 green flashes = "44", means no problems.
7.) refer to Haynes manual for meaning of code (DO NOT USE various codes posted on the interent as most are not reliable for this particular ECM unit (#40).
8.) code 44 means everything is OK
9.) you may have to drive the car around to generate error codes that occur during driving!
10.) To clear all codes, unplug the wiring harnesses from the ECM unit when ignition is off.
11.) Best way to read codes is by removing the passenger seat (then you can see the flashing LEDS while your driving!).