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scionking
scionking, toyota expert
Category: Toyota
Satisfied Customers: 243
Experience:  5 YRS EXP. ASE MASTER CERTIFIED/ TOYOTA MASTER CERTIFIED
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Toyota Corolla DX I have a 1994 Toyota Corolla DX, 1.8L with

Customer Question

I have a 1994 Toyota Corolla DX, 1.8L with 222k miles.

Engine light came on and it started running rough. The problem went away the following day but showed up again about 1 week later.

The OBD1 Code read 41(Throttle Position Sensor) so I replaced the TPS and calibrated per instructions in a Haynes repair manual

After hooking everything back up I test drove the car. It lacked power and the Catalytic Converter was glowing red after the test drive. The check engine light remained on with a OBD1 code of 12 (No RPM Signal to ECM)

I assumed the problem was a blocked CAT so I replaced it. I also installed a new distributor cap, rotor, plugs, and wires. This did not fix the problem. Still lacks power and the new Cat glows red after running a few minutes.

It is obviously not burning the fuel completely. I assume it is a timing issue. Could it be a bad ECM? The original TPS I replaced was not that far out of tolerance which makes me think it could be a bad ECM. Any ideas?
Submitted: 3 years ago.
Category: Toyota
Expert:  scionking replied 3 years ago.

From what your describing is sounds like engine is running extremely rich,I would inspect intake for restrictions(mouse nest),if you have access to a compression tester through a parts store rental i would recommend preforming one since there is significant millage on car, next inspect fuel injector, its possible and ive seen it before were these will have leaking injectors and glowing catalitic converters, if tips of injectors have staining on the spray nozzles replace stained injectors, also inspect oxegen sensor for correct voltage(Haynes should have a test for this), if oxygen sensor is lazy or out of range it will cause excess fuel to be dumped into engine. Code 12 is usually caused by the crank sensor inside distributor and requires distributor to be replaced.Bad ECM is usually not the case, however not totally out of the question.

scionking, toyota expert
Category: Toyota
Satisfied Customers: 243
Experience: 5 YRS EXP. ASE MASTER CERTIFIED/ TOYOTA MASTER CERTIFIED
scionking and other Toyota Specialists are ready to help you
Customer: replied 3 years ago.
I checked the compression. It was not great (about 150 per cylinder) but within the acceptable range according to Haynes. There are no restrictions in the intake and it has a new air filter. All of the injectors were clean. The O2 sensor did seem to have a problem so I replaced it. It runs better with the new O2 sensor but it is still not running as well as it did a few weeks ago. It still lacks power and the CAT still glows after running it a while. I have not replaced the distributor yet and still getting code 12. This code only showed up after the original problem with the code for the TPS Sensor. Even though I replaced the TPS the old one was not that far out of tolerance. I checked all of the electrical connections to all sensors and cleaned them with contact cleaner. With the Code 12 Bad Crank Sensor, would that affect how the ECM calculates fuel mixture? Any ideas on what to try next? With so many miles on the car I hate to keep throwing parts in to it. Thanks

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