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Greetings-Need help with poor/rough idle, car dies when given some throttle
Hello everyone – excited to finally join the community as more than just a lurker.
I’m currently working through some issues with my dad’s 1990 Camaro IROC-Z. He bought it brand new off the showroom floor in 1991, and ever since I was old enough to appreciate cars, this one has held a special place for me. It’s always been “cool” in my eyes, and now I’m on a mission to preserve it, maintain it, and hopefully improve it a bit too.
My dad likes to reminisce about what the car used to be, while I tend to focus on what it still is—a fun, head-turning cruiser, especially on a sunny day when I’m sporting the mohawk.😎
For the better part of two years, the IROC has been sitting in a barn. Prior to being parked in the fall of 2022, it was starting to show some frustrating signs. It ran fine for short trips, but after a 10–15 minute drive, it wouldn’t want to start back up. And if it did start, it would idle OK until I put it in gear and gave it a little gas—then it would stall. Somehow, I never got stranded, but I just chalked it up to the quirks of an old car at the time.
Now I’m ready to bring it back to life for summer, and I could really use some help from the community.
I’ll be the first to admit I’m not a mechanic—I can change oil, swap wiper blades, check fluids, and I rely heavily on YouTube University for everything else. I’ve searched the forum and tried several commonly recommended fixes, though it’s possible I’ve made a few rookie errors along the way.
Here’s what I’ve done so far:
Replaced the IAC valve
Replaced air filters
Cleaned the IAC port and throttle body (to the best of my ability—open to being corrected)
Cleaned the QC connections
Verified that the fuel pump is working and electrical readings look solid
I have not removed the throttle body for a deeper clean, as I’m not convinced that’s the root issue. I’m wondering now if the O2 sensor could be a culprit, or if I’m overlooking something else entirely.
My goal at this point is just to get the car running well enough to drive it to a shop instead of having it towed.
I’ll be attaching some videos (YouTube links) for reference—any and all feedback, suggestions, or encouragement is greatly appreciated!
From: Franklin, KY near Beech Bend Raceway, Corvette Plant and Museum.
Car: 1992 Pontiac Firebird
Engine: 5.0L L03 TBI
Transmission: 700R4
Axle/Gears: 2.73
Re: Greetings-Need help with poor/rough idle, car dies when given some throttle
Take a picture of the engine in your Dad's IROC-Z that replicates the picture below so we can see which fuel injectors are installed in the engine now. Look over the engine and verify that all 8 fuel injectors are the same as the two you took a picture of for us. If any of them are different then take a picture of them too. They liked to get cute back in the day and only replace the RP Multec fuel injectors that tested bad instead of all 8 of them. They are all bad even if they test good. All 8 RP Multec fuel injectors are bad and go straight into the trash without testing. RP Multec fuel injectors that test "Good" are little hand grenades with the pin pulled so far out it's hanging on for dear life and the least little thing to disturb it and it falls out and RP Multec goes BOOM!!!
The insulation that Rochester Products used to coat the wire of the "voice coil" that drives the pintle up and down inside the injector can't stand up to alcohol, harsh solvents, HEET, gas treatments, fuel injector cleaner that wasn't approved by GM for use with RP Multec fuel injectors. Pretty much they can't stand up to anything that wasn't real pure gasoline back in the mid 1980's.
Multiple things can be wrong with the car at the same time for a car this old that has sat for so long. If the engine still has the defective RP Multec fuel injectors installed then trying to address any other issues it has before replacing the fuel injectors with the proper brand new Delphi fuel injectors designed to be a 100% drop in replacement for the RP Multec fuel injectors is the same thing as pissing into the wind.
1989 to 1992 RP Multec Fuel Injectors. Retroactively Defective by Design.
Re: Greetings-Need help with poor/rough idle, car dies when given some throttle
Sure thing. I believe they have been replaced in last 10 years but I will definitely get some photos uploaded when I get a chance. Thank you for your input sir.
