Rough idle
Thread Starter
6th Gear
Joined: Jul 2023
Posts: 6
Likes: 1
Rough idle
So I own a 1989 corvette base model, and I've been having trouble on finding out this rough idle issue. when I last drove it, it kept cutting out entirely and turning off. I've replaced everything on the TB as well as deep cleaning it with a toothbrush and tb cleaner. I also have a new cap, rotor, ignition module, and new plugs and wires. I have also cleaned the MAF as well as a new fuel pump and filter. I did recently get stranded with no gas and it's acted weird ever since. It mainly gets rough whenever the idle drops from the initial startup.
Racer
Joined: Aug 2014
Posts: 478
Likes: 66
From: Elizabethtown, NC
So I own a 1989 corvette base model, and I've been having trouble on finding out this rough idle issue. when I last drove it, it kept cutting out entirely and turning off. I've replaced everything on the TB as well as deep cleaning it with a toothbrush and tb cleaner. I also have a new cap, rotor, ignition module, and new plugs and wires. I have also cleaned the MAF as well as a new fuel pump and filter. I did recently get stranded with no gas and it's acted weird ever since. It mainly gets rough whenever the idle drops from the initial startup.
Drifting
Joined: Apr 2011
Posts: 1,925
Likes: 441
From: Albuquerque NM
1989 rough idle over here also. Sorta high. Averages 800 RPM.
Plugs are around 10k miles old. Did IAC and TPS calibration procedure, problem persists. All new plug wires, problem persists.
Took throttle body off, deep cleaned it, new IAC. Haven't done the the calibration procedure but idle still rough. Car doesn't pull as hard as I feel it should.
Any ideas what to do next?
Plugs are around 10k miles old. Did IAC and TPS calibration procedure, problem persists. All new plug wires, problem persists.
Took throttle body off, deep cleaned it, new IAC. Haven't done the the calibration procedure but idle still rough. Car doesn't pull as hard as I feel it should.
Any ideas what to do next?
Advanced
Joined: Jul 2023
Posts: 57
Likes: 3
From: Connecticut
This might sound dumb but have you checked your battery voltage? Low alternator output will cause a rough idle and its an easy fix. Do you have a fuel pressure gauge? An issue like this would be very noticeable on a gauge. I know you replaced your plug wires and have a relatively refurbished distributor, but have you actually checked for spark at each cylinder? Plus plugs? A dirty plug can tell you a lot. If you have a borescope you could also see carbon buildup on cylinders when checking plugs.
I've had this issue a few times, first was my distributor, though its pretty expected from an optipark. It acted very similarly to what you're describing, id recommend checking everything related to spark first. Next was my alternator, replacing worked just fine. Fuel pressure also screwed me over before I replaced the pump and deleted the stupid regulator thing in the pump assembly. Being as mine is a 94 it will be slightly different but all engines need fuel spark and air. Diagnosis is your friend.
I've had this issue a few times, first was my distributor, though its pretty expected from an optipark. It acted very similarly to what you're describing, id recommend checking everything related to spark first. Next was my alternator, replacing worked just fine. Fuel pressure also screwed me over before I replaced the pump and deleted the stupid regulator thing in the pump assembly. Being as mine is a 94 it will be slightly different but all engines need fuel spark and air. Diagnosis is your friend.
