Vt V6 3.8L trying to stall

[Regularmaintinence]

Hi just looking for some advice.
VT V6 3.8l

idles great, runs great.

PROBLEM~ INTERMITTENT while idling (in gear) at traffic lights, car seems to be trying to stall. Occasionally while driving (any speed) car does the same.
DOES NOT happen while idling in park (just flushed radiator idled for about an hour in park no problem)
ONLY happens when in gear.

the car was intermittently stalling out completely, but has improved a lot but still intermittently (tries) to stall.

improvement after:

-changed oil pressure switch
-removed and cleaned throttle body
-removed and cleaned MAF (mass air senso)
-adjusted (factory) throttle screw (stepper) on throttle body
-new plugs
-new leads

OBD results - the ONLY error message was mass air flow sensor “out of range”

car has mods
cold air intake
headers
3.5 inch exhaust

(RECAP)
car runs great for days at a time
occasional intermittent episode of “trying to stall” but recovering“
this happens while idling at lights
this also happens while driving at any speed.

Ill be doing 80kph for example and car will slightly cut out, recover for a few seconds then run normal.
-used to stall out completely before doing the “things“ I mentioned
now it just “tries” to stall but recovers .

problem can go away completely for a week or two (200-300kms)

seems to be worse with “air conditioning on”
(oddly) idle speed stays the same weather air con is on or off about 800RPM
SHOULD go a bit higher with air conditioning on surely?

again car is fine 90% of the time issue is intermittent and no apparent pattern.

 

[Immortality]

Idle seems a bit high.

checked for vacuum leaks?

Check the fuel pressure/ change the fuel filter?

How much petrol does it use? is it lacking power?

Engine temp normal?

Can you borrow another MAF to test with?

 

[Regularmaintinence]

-Vaccum leaks checked, hoses reseated and sealed with silicone.
-no errors in OBD relating to fuel system
-no spare MAF sensor

 

[Regularmaintinence]

Fuel is high because transmission holds 3RD gear longer than it should at 70kmph. If I go slightly slower or faster it goes into third.
engine temp normal.

 

[Immortality]

No sensors in the fuel system. Need to check manually.

Transmission shifting at weird times might suggest a problem with the TPS.

 

[Regularmaintinence]

Thanks, TMS runs in line with my instinct of "electrical short. Feels like a disruption in the "electrical" system.
TMS module is defiantly in that area.
again I have no data, running on gut feel that there is an electrical disruption.

thanks.

 

[lout]

what scan tool are you using
what live data and fuel trims do you have

 

[Regularmaintinence]

Not sure model, but whatever RAA OBD 1 has.
scanned by RAA.
trims set by RAA To factory defaults.
was running perfectly at the time.

issue is random intermittent, would have to have scan tool plugged in for two weeks to get associated live data on event.

1 error on historical data: MAF sensor "out of range"

otherwise completely clean.
live data "in normal range"

slightly running rich but ok for age and cold air intake, headers. Both cylinder banks running 2-4% rich but even.
done 270,000kms so would expect that even without the mods.

not been "dyno" tuned for mods for peak performance but running within factory spec.

have replaced ALL coils 3 years ago. One was bad replaced all 3 to be sure.

it "feels" like an electrical short.
just hard to diagnose due to being "intermittent"

 

[Regularmaintinence]

The VT tolerances are fortunately generous or some would say "sloppy" with the mileage and mods the data is all "within" acceptable range.
in a current Carrera gt the computer would be having a $23,000 fit.

in the VT the data is more than fine.

 

[lout]

looking at live data often shows problems with out the glitch
fuel trims are spot on which means O2 sensors are reporting correctly and no vacuum leaks
i would be replacing engine relay under bonnet fuse box as a guess
be careful type A and type B relays
and have a good look at plug connector to DFI module