Strange issue with timing Fixed

[2003 mustang gt modded]

Hi, I have 2003 gt, just replaced O2 sensors with motorcraft ones and replaced ignition coils.

While checking engine parameters I noticed timing is eradic, and keeps jumping to 31 deg. And down to 14 deg every couple of seconds at idle. It runs descent at Wot.

I was thinking it might be cam sensor since it was dirty and was little oily. Or icv as mentioned by cars original owner.

Any suggestions will help. Thanks.

 

[2003 mustang gt modded]

Does some know why timing is all over the place at Idle, it keeps jumping to 31 deg back to 15 deg and up again to 30s.?

When driving it goes back to normal steady timing?

Is this damaging my engine?

 

[RaggedGT]

With it being a completely computer controlled mod motor-I’d say that’s pretty normal. If it wasn’t, you would have a list of timing component engine codes to go along with it

 

[2003 mustang gt modded]

I can’t upload the file, I was seeing 41 deg advance timing spike. Is that normal? Engine is modified and Ecu was flashed.

 

[Noobz347]

Common Causes of Erratic Timing​

Dirty or sticking Idle Air Control (IAC) valve

The PCM uses spark advance to counter idle airflow fluctuations. If the IAC sticks, the PCM will chase the idle with spark.
Check: If idle RPM drifts or hunts along with the timing, pull and clean the IAC with throttle-body cleaner.


Vacuum leak (unmetered air)

A small leak near the intake manifold, PCV hose, or vacuum tee can cause erratic idle fuel trims and timing correction.
Check: Spray carb cleaner around suspect areas and listen for RPM changes, or use a smoke test if available.


Camshaft Position Sensor (CMP)

A weak or oily CMP can cause timing instability at low RPM if the signal is noisy. The 2V engine uses it for sequential injection and ignition phasing.
Check: Inspect connector and wiring; replace sensor if there’s oil intrusion or intermittent signal in a scan log.


Crankshaft Position Sensor (CKP)

Less common, but a marginal CKP can cause the PCM to re-sync timing constantly.
Check: Look for consistent RPM signal in live data — any dropouts mean it’s time to replace it.


Fuel trims and O₂ feedback

You just replaced the O₂s — verify both are switching normally (~0.1–0.9 V) and trims are close to ±5% at warm idle.
If one bank’s trim is off, the PCM will vary spark on that side to chase stoichiometry.

 

[2003 mustang gt modded]

B2err-body
DAT
P015C

Thank you for replying previously.

 

[2003 mustang gt modded]

Got it, thanks a lot.

 

[2003 mustang gt modded]

It was crank position sensor and connector. Thx Noobz347.

There is another issue with the car. Who ever tuned the car, put too much timing advance at 35 deg. @ 1500-2000 rpm.

The long tube headers get really hot, and the clutch as well. And I think it will damage clutch eventually.