Need Help/Ideas with random idle issue

[benf]

2012 Camaro LFX with stock internals, just bolt ons. The engine is a replacement from a 2015 with 7k miles on it installed 2 months ago. Never had the issue with the original motor. The car randomly will fluctuate timing/TPS readings at idle. The logging looks like a heartbeat. Timing will vary from -3 up to +25 degrees and TPS 1.6 up to 4%, then repeats. It doesn't do this every time i stop, but a lot of the time which makes it harder to diagnose. So far i have replaced the intake and TB gaskets, MAF sensor, Purge Solenoid, Brake booster check valve, and the hoses to my catch can. Car drives good and ltft while driving are +/- 3%. Any ideas?

[benf]

Tried an experiment....if i turn on the AC while it is doing its surging, it stops fluctuating so much and smooths out. Here is a pic of what i am looking at...u see the spikes then smooths when i turn AC on

[benf]

So much for the AC turning on clearing it up...just tried it again and no effect...

Could the TPS be causing it?

[tlavoie87]

did you modify the MAF freq?

[benf]

did you modify the MAF freq?

Yes...its weird that it does this now that I replaced my motor in september and that is when this started. Did not do this on the old motor with same setup and same tune. I have tried multiple older tunes, but still same issue. What makes it even harder to figure out is that it is random, doesn't do it all the time.

I have now replaced Plugs, maf sensor, TPS/Throttle body, Gas pedal/APP sensor, intake gaskets, TB gaskets, purge solenoid, brake check valve, crank position sensor, and catch can hoses.

[benf]

as a test, I was idling and while it was doing its surge thing I pulled the connector off the gas pedal and the surge stopped and idle leveled out.

[tlavoie87]

hmm..by any chance do you have a VTC installed?

[benf]

hmm..by any chance do you have a VTC installed?

Yes, and i thought the same thing, but it did it even with it disconnected. Right now i am replacing my 4 o2 sensors. I have 98k miles on it and figure it couldnt hurt. I have replaced 3 of them already and waiting for the 4th to show up today. Does seem to have the issue less often now, so maybe there was an issue with the sensors cause i never cleaned them after i blew the last motor up. Guess the real test will be after i get the 4th sensor installed.

[MarkTucker]

If you still have the issue, post up a log of it when it is happening.

And also included your list of modifications.

[benf]

Here is a short log showing whats going on. I have now replaced the 4 o2 sensors as well and the issue remains. Being that it doesn't do it all the time its hard to diagnose. Does it a lot though..

I also did the Throttle Cleaned function..no help

Issue starts at 1:02 on the log file posted

[MarkTucker]

Can you post up the tune and also your list of modifications?

[benf]

Mods are e85, 80mm tb, Solo high flow converters, under drive pulley, CAI, and HP Tuners, VTC. 3.91 gears, 3800 Circle D convertor.

[MarkTucker]

And you had the larger throttle body and the VTC installed on the previously engine with the same tune?

If so, it didn't have this issue?

[benf]

Never had the issue with the setup on the old motor. Everything is the same minus the nitrous. Like I mentioned, I tried older tunes and same issue.