l86 dod delete: stalling and inconsistent idle after startup

[persistent]

i've completed the mechanical work for a dod delete on my 2020 l86, and i'm having issues with inconsistent idle and stalling after starting the car up. i have used hp tuners to download ecm, flip dod setting to disabled, and written the modified image back to ecm.

here is a summary of what i've swapped out during the dod delete work:

- replaced stock camshaft with TSP-316804 "oem-style non-dod" camshaft
- replaced stock lifters and pushrods with BTR LS7 lifters and 7.800" pushrods
- installed oil port plugs under vlom cover
- replaced vacuum pump with oem part
- replaced water pump with oem
- replaced phaser sprocket and timing chain with oem
- replaced oil pump with oem
- replaced valve seals, springs, caps, and rockers with oem

here is a summary of what i've done in terms of the work:

- checked the timing marks lined up between phaser sprocket and camshaft sprocket several times before closing the timing cover
- followed service manual instructions to apply upward pressure to new oil pump while tightening fasteners
- walnut blasted and manually cleaned intake ports on heads
- removed nearly all carbon buildup on intake valves
- primed the oil system by using a starter relay bypass tool prior to starting engine
- all fluids have been changed, including transmission fluid, but i have not yet flushed and brought transmission fluid level up from what i pumped into the pan (4 qts)

i have let the car idle for a total of roughly 5 minutes so far, and i decided to shut it off in case something was wrong with it. i saw the tachometer start fine, the rpms drop below 1k, and it would dip towards zero episodically. in some cases it stalled straightaway on start.

i'm unsure what steps i should take to diagnose and fix the idle problem. maybe i just need to let it idle for a while to warm up or tune it further, but i have no experience doing this.

EDIT: something else i thought could be relevant is that this car has sat for 3 months while i worked on it. perhaps stale gas could be an issue.

 

[persistent]

i've started the car again and it does idle without trouble, but i'm seeing and hearing a yoyoing between 450 and 750 rpm. in vcm scanner, the timing advance goes from 0 deg to 30 deg before dropping back to 0 deg and repeating with the engine speed yoyo.

 

[persistent]

talked to a friend of mine that has a lot of track cars, and he suggested i check the camshaft position sensor and cabling after i mentioned the unstable timing advance.

sure enough, i checked the 3 connectors on the timing cover and 2 of the 3 were not locked into position with the tabs down. reseated 1 of the connectors, pushed in 2 retaining clips, and now it's got a steady idle. the timing advance value has stabilized substantially from the prior behavior of it sawtoothing.

 

[persistent]

hmmm. looks like i spoke too soon. while i was flushing the transmission fluid and idling today, the problem has returned.

any thoughts on what to look at, e.g. camshaft position sensor? i'm pretty confident this isn't an issue with the timing of the camshaft and crankshaft.

 

[Geotrash]

hmmm. looks like i spoke too soon. while i was flushing the transmission fluid and idling today, the problem has returned.

any thoughts on what to look at, e.g. camshaft position sensor? i'm pretty confident this isn't an issue with the timing of the camshaft and crankshaft.

Given that reseating the connector helped right away, I would still suspect that there is a problem with it.

You need a good bi-directional scanner that will let you see various parameters such as fuel trims and data on the camshaft advance, etc., in order to pinpoint the cause. If you have access to HPTuners, that would work for gathering the data.