1987 SE , Manual , 88K miles

Hello friends ,

I need advice. A week ago, I started getting the CEL during driving and the engine RPM would fall below 1K at slow & idle speeds. I checked the code by connecting a wire to the connector next to the cigarette lighter knob and it blinked as a 45 Code. I changed the fuel filter and still got that 45 code. I then bought a new O2 sensor, but this time after reconnecting the battery and start up, the RPM went to 2,500 RPM remained running like that. The CEL had come on 30 seconds after start up. Please let me know your input were to go from here. Your feedback would be greatly appreciated. Thank you.

quote Originally posted by MERATIME: ...45 Code

How many of the checks listed on This page have you done? And what were the results?

quote Code 45 - Oxygen Sensor - Rich Exhaust The ECM will set code 45 when the ECM detects a high voltage from the oxygen sensor, throttle is applied and the system is operating in Closed Loop (conditions must exist for longer than 50 seconds and engine must be running for at least 1 minute). -Check the oxygen sensor and replace if necessary. -Check fuel pressure. The system will go rich if the fuel pressure is too high. -Check for rich injectors. -Check for leaking injectors. -Check for fuel contamination (specifically for contamination with oil). -Check for proper ignition module shielding. If the ignition module is not properly shielded, the ECM might mistake the electro-magnetic interference for reference pulses, causing too much fuel to be delivered to the system. -Check the canister purge for fuel. If full, check canister control and hoses. -Check the MAP sensor. If the ECM detects a lower than normal vacuum then this will cause the system to go rich. Disconnect the MAP sensor. If the rich condition goes away, then a problem exists with the MAP sensor. -Check for leaking fuel pressure regulator by checking the vacuum line to the regulator for fuel. -Check TPS. An irregular TPS output will cause the system to go rich due to a false indication of accelerating.

IMO, anyone troubleshooting an engine issue with their Fiero should be making use of a scanner and/or WinALDL. Otherwise, everyone's just guessing. Checking the fuel pressure with the engine running and after the engine's been turned off also provides invaluable information.

[This message has been edited by Patrick (edited 05-17-2025).]

I reviewed and followed this link given. As said previously and will add specifics, the SES would first blink1..2.. (3 times. Then blink 4..5.. (3 times) , and then the closing 1..2.. routine.

Patrick, I also wanted to mention this if this helps. This Fiero has been out of commission for over 1 year. And I wanted to make sure I am starting this vehicle correctly. I have been starting this car by turning the key to the ACC selection until the fuel pump engages and stops humming and then I would turn the key to on to start and it would start up, and that was where the RPM would stay at 2500 for a long period of time and the SES light would come on in about 30 seconds.

My question to you is: could this code 45 be happening due to fuel being primed prior to turning the key to on position?

This morning, I started the car normal turning the key pass the ACC straight to on and there was no high rev. going past five seconds and no SES.

What I am asking is if there is a specific way to start these TECH-4 engines at this age? Thanks.

[This message has been edited by MERATIME (edited 05-17-2025).]

Curiuos, what brand Q2 sensor did you buy?

quote Originally posted by MERATIME: 1987 SE , Manual , 88K miles

Ok, first of all... please mention in your description what engine you have. So many Fiero owners who've posted here over the years have simply stated that they have an "SE", apparently not realizing that this model could have either the 2.5 Duke or the 2.8 V6 engine.

quote Originally posted by MERATIME: I also wanted to mention this if this helps. This Fiero has been out of commission for over 1 year. And I wanted to make sure I am starting this vehicle correctly. I have been starting this car by turning the key to the ACC selection until the fuel pump engages and stops humming and then I would turn the key to on to start and it would start up, and that was where the RPM would stay at 2500 for a long period of time and the SES light would come on in about 30 seconds. My question to you is: could this code 45 be happening due to fuel being primed prior to turning the key to on position?

That's the way I start all my cars, Fieros and otherwise. This starting procedure is itself (with a properly running engine) not a problem.

quote Originally posted by MERATIME: This morning, I started the car normal turning the key pass the ACC straight to on and there was no high rev. going past five seconds and no SES.

The only thing I can think of is that you've possibly got a leaky injector (and/or fuel regulator), and by not fully priming the fuel line before starting, less gas has pooled at the leak and this has affected how the engine starts. Or possibly the ECU has simply reset itself and there's no longer an issue.

quote Originally posted by MERATIME: What I am asking is if there is a specific way to start these TECH-4 engines at this age?

No. (As with all fuel injected engines, keep your foot off the gas pedal when starting it.) But now that we've been informed this is a duke engine we're dealing with (and if the problem returns)... have someone turn the ignition key to prime the fuel line (without starting the engine) while you're looking down into the throttle body (with the air filter lid removed, obviously). See if gas is oozing/spraying out of the fuel injector. There should be no gasoline evident at all.

Patrick, Thank you for providing your feedback behind Code 45 plus the advice. Please pardon my knowledge about the SE,,, I thought the SE was a base model Fiero including a 4 Cyl engine only. Haha… now I know and appreciate your clarification

I will look into the steps that you recommended.
Thanks again!