**Resolved** After replacing the O2 sensor and other things on my 1989 K5 its lugging and idling poorly

[dyeager535]

If you can repeatedly trigger this ONLY locking the converter, I'd lean towards a converter/trans problem.

While it is going lean, and it is knocking (and likely pulling timing) if the problem you are experiencing is only during TCC lock, I dont see anything in the logs indicating there is a serious issue with the way the EFI is operating. For it to actually feel like a rumble strip, it would take a LOT of knock, and you are right, it's not there. Your TCC from what I make of it seems to be working properly (unlocking prior to shifting).

TPS base level is self-resetting on TBI IIRC, probably not an issue.

TBI is extremely slow on data speed, so a lot can happen between the data points that might show with much faster data updates.

Fwiw, this guys post isnt bad, and tunerpro seems to show spark advance (in his linked video on Google drive) https://forums.ifsja.org/forum/tire...rom-gm-based-tbi-system-like-howell-for-cheap

On the "normal" log you posted that I evaluated, did it do the same thing every time TCC was locked?

 

[clutch2k3]

Updates:
- The trans shop test drove it and strongly believes its an engine issue, not a transmission issue - and now I think they're right.
- I bought a smoke tester and discovered that the EGR valve was leaking. I replaced it with a block-off plate and it solved the hunting-idle issue. This also reduced the surging at cruise a bit but its still present.
- After blocking off the EGR datalogs are now showing a consistent lean condition during TCC Lockup with BLM cell values of 130-142 and incrementing knock counts in the problem areas.
- I rented a fuel pressure test kit from O'Reilly's and the gauge is showing 12+ PSI at idle (after the fuel filter).
- New injectors didn't help the surging during TCC lockup I'm replacing the injectors tonight

The thing that blows my mind is that the EGR & injectors were working fine up to the minute I drove the truck into my garage before working on it this summer. During the 6 weeks of work I did on it I didnt touch the EGR or injectors. The EGR valve was bought in April 2024 and died in July 2025 after not being used for 6 weeks (the injectors and fuel pump were also replaced in April 2024).

IMO a smoke tester is required for finding vacuum leaks. This is what I used (under $100 total):
- Smoke tester macine: https://www.amazon.com/dp/B0C7MKZPK3
- Smoke tester oil: https://www.amazon.com/dp/B08G1GRV7T
- Smoke tester adapter: https://www.amazon.com/dp/B0CJ2PLNDZ
- O'Reilly's FP rental kit with a GM TBI adpater: https://www.oreillyauto.com/detail/...s-evertough-fuel-pressure-test-kit/ren1/67091

View attachment 2025-11-19 17.26.45.mp4

 

[clutch2k3]

@dyeager535 apologies, I missed your valuable post.

AFAIK, yes, the data logs look the same (basically "OK") every time TCC is locked since July of this year.

I agree, I don't see anything in the data logs indicating a serious issue, definitely not an engine issue that would rattle the interior of the vehicle like going over rumble strips. While I don't believe the data logs are showing "perfect" engine behavior, I don't expect them to for a 36 year old SBC with a dinosaur of an EFI system. If it were solely an engine issue, I'd expect something to jump out in the data logs

I agree, after verifying FP and replacing the injectors I'm back to thinking the primary cause is a trans issue, regardless of what the trans shop is telling me. The owner of the trans shop I use is a bit stubborn, overwhelmed with work and in his defense, the engine might not be running like a sewing machine at the moment. But either way, I'm going to find another trans shop. Also, on August 19 this year the PR valve "fell out" of the pump. While I'm not 100% sure that the TCC material is worn, my understanding is that there are other fluid pressure issues specific to the TCC circuit that could cause the TCC to grab and let go.

Thanks for mentioning TunerProRT!!! I had no idea injector duty cycle and ignition timing are available from TBI ECMs. This whole time I thought WinALDL was providing all available data from the ECM. I just made my $40 donation for a TunerProRT registration and should have it working within the next day or so.

As it turns out that video was for an ECM with a custom ROM (Howell?) and tunerpro will not work with stock TBI ECM ROMs and stock TBI ECM ROMs do not output all the data we'd like to see.

 

[clutch2k3]

Root cause was bad spark plug wires and crossfire.

The spring clips inside the plug-side boots were loose (AC Delco wires less than 1.5 years old). I replaced the wires and the issue improved but didn’t fully go away.

Final fix was securing the wires so they absolutely could not cross, especially near the distributor. I used zip ties to control routing and separation. Once the wires were properly isolated, the problem disappeared.

I had previously tried rerouting to prevent crossfire, but the loose plug boot terminals were still causing inconsistent spark, so it never fully resolved until both issues were addressed.

Thanks to everyone who chimed in and helped troubleshoot.