Surging while in gear
Thread Starter
Intermediate
Joined: Jan 2025
Posts: 47
Likes: 3
Surging while in gear
A few days ago, I got a code 44 on my C4 (L98) after driving on the highway for about 30~ miles. While driving at highway speeds, it seemed like that whenever I let off the throttle the engine would miss. After I got off the highway my car started to surge from 600-900rpm continuously when stopped the rest of the drive. My fuel pressure is up to spec as well as the rest of the fuel system, I don't have any vac leaks, (That I know of), and my spark/timing seems to be ok. I have no clue what could be causing this problem! Any help will be appreciated because its driving me insane!!! 
Race Director
Joined: Nov 2003
Posts: 12,220
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Next logical suspect is an injector (or multiple injectors). Have you measured their ohms...while running (hot) yet? (target should be 16ohms)
Melting Slicks
Joined: Aug 2003
Posts: 3,380
Likes: 388
From: Lakeville MI
Its pretty tough to get a code 44 without something being seriously wrong (unless the fuel trims have been severly limited in the tune). It requires the O2 voltage to be less than 199 mv for 50 seconds while in closed loop with the integrator active (not forced to 128 due to running below the minimum injector pw, such as in DFCO).
Contaminated fuel?
What year car?
It doesn't take much to excite a surge. Typically excess airflow/high idle rpm getting into an unstable region of the spark advance table causing big swings in spark advance with rpm and load variation.
Contaminated fuel?
What year car?
It doesn't take much to excite a surge. Typically excess airflow/high idle rpm getting into an unstable region of the spark advance table causing big swings in spark advance with rpm and load variation.
Last edited by tequilaboy; Jan 13, 2025 at 03:03 PM.
Thread Starter
Intermediate
Joined: Jan 2025
Posts: 47
Likes: 3
Turns out that my EGR Valve was stuck in the open position, meaning it was constantly letting some exhaust back into the engine. It's original from 1986 so it makes sense it finally failed. Replaced it and now she's running as good as new! 
