1984 C4 idle/ throttle issue
Thread Starter
4th Gear
Joined: Feb 2025
Posts: 4
Likes: 1
1984 C4 idle/ throttle issue
Hey everybody, I hope you are all doing well. First time poster here looking for some help! Ok so I’ve got a 1984 with just under 90k miles. I’ve been having a hunting idle issue where the car will jump from 500-900 only while in park pretty consistently. Sometimes it’ll go from 300 all the way up to 1400, in the worst cases the car will even bog down and stall out and not start back up until I’ve let it sit for a good while. Only really have the issue after driving for a bit and the car is fully warmed up, starts and idles just fine off a cold start. On top of this no matter how much or how little gas I give the car it responds pretty erratically jumping forward one second only to act like theirs no fuel the next all the while my foot doesn’t move on the gas pedal. Under full throttle the car either one, bogs out and dies, or two races forward only to bounce off of 2000 rpm’s speeding up gradually before upshifting and getting caught at 2000 rpm’s again almost like theirs a rev limiter. I’ve already done the IAC sensors, Egr valve, fuel
filter, and adjusted the tps to .524 along with checking all my lines for a vacuum leak. Any help would be greatly appreciated!
filter, and adjusted the tps to .524 along with checking all my lines for a vacuum leak. Any help would be greatly appreciated!
Last edited by Ephrem; Feb 15, 2025 at 05:24 PM.
Burning Brakes
Joined: Sep 2017
Posts: 933
Likes: 165
Burning Brakes
Joined: Sep 2017
Posts: 933
Likes: 165
Hey everybody, I hope you are all doing well. First time poster here looking for some help! Ok so I’ve got a 1984 with just under 90k miles. I’ve been having a hunting idle issue where the car will jump from 500-900 only while in park pretty consistently. Sometimes it’ll go from 300 all the way up to 1400, in the worst cases the car will even bog down and stall out and not start back up until I’ve let it sit for a good while. Only really have the issue after driving for a bit and the car is fully warmed up, starts and idles just fine off a cold start. On top of this no matter how much or how little gas I give the car it responds pretty erratically jumping forward one second only to act like theirs no fuel the next all the while my foot doesn’t move on the gas pedal. Under full throttle the car either one, bogs out and dies, or two races forward only to bounce off of 2000 rpm’s speeding up gradually before upshifting and getting caught at 2000 rpm’s again almost like theirs a rev limiter. I’ve already done the IAC sensors, Egr valve, fuel
filter, and adjusted the tps to .524 along with checking all my lines for a vacuum leak. Any help would be greatly appreciated!
filter, and adjusted the tps to .524 along with checking all my lines for a vacuum leak. Any help would be greatly appreciated!
Pro
Joined: Mar 2024
Posts: 537
Likes: 379
From: Northern California
My guess is that it has to do with the ignition coil. Your symptoms sound eerily similar to when my 1989 Celica was giving me coil issues. Even though they're VASTLY different cars, the physics should still work the same for this type of ignition system.
My main reason for believing its ignition related is due to the fact that you say the car starts off cold perfectly fine. Typically things like faulty ignition parts go wonky (scientific term) when they have soaked up some heat from driving. I sadly don't have my FSM on this computer that I am typing on, but I can open it up tomorrow and see if there's a page to diagnose a faulty coil or ignition issue so you don't just throw parts at it.
My main reason for believing its ignition related is due to the fact that you say the car starts off cold perfectly fine. Typically things like faulty ignition parts go wonky (scientific term) when they have soaked up some heat from driving. I sadly don't have my FSM on this computer that I am typing on, but I can open it up tomorrow and see if there's a page to diagnose a faulty coil or ignition issue so you don't just throw parts at it.
Thread Starter
4th Gear
Joined: Feb 2025
Posts: 4
Likes: 1
I checked it out and it looks like the previous owner already replaced it, it looks brand new and I can see where he spliced in the new connector.
Thread Starter
4th Gear
Joined: Feb 2025
Posts: 4
Likes: 1
My guess is that it has to do with the ignition coil. Your symptoms sound eerily similar to when my 1989 Celica was giving me coil issues. Even though they're VASTLY different cars, the physics should still work the same for this type of ignition system.
My main reason for believing its ignition related is due to the fact that you say the car starts off cold perfectly fine. Typically things like faulty ignition parts go wonky (scientific term) when they have soaked up some heat from driving. I sadly don't have my FSM on this computer that I am typing on, but I can open it up tomorrow and see if there's a page to diagnose a faulty coil or ignition issue so you don't just throw parts at it.
My main reason for believing its ignition related is due to the fact that you say the car starts off cold perfectly fine. Typically things like faulty ignition parts go wonky (scientific term) when they have soaked up some heat from driving. I sadly don't have my FSM on this computer that I am typing on, but I can open it up tomorrow and see if there's a page to diagnose a faulty coil or ignition issue so you don't just throw parts at it.
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