u/flykinx_d3k0

Quick background: bought this car recently coming from BMW land and was geeking out with a Durametric kit trying to understand what baseline looks like on a 996. That's actually how I discovered the issue - the car ran fine when I bought it and the previous owner drove it hard with no complaints. Bank 1 was reading -11.48° at idle, Bank 2 was fine at -4.14°. I only flagged it because I knew the spec was ±6°.

Took it to a shop who retimed the engine in-car, had it for a month, said the timing held, and returned it. Drove it home and it jumped again. Now reading Bank 1 at -10.9° and Bank 2 at +7.7° - both banks out of spec and in opposite directions.

When the shop did the retime they pulled the oil pan and inspected for plastic and metal debris. Found nothing. Does that meaningfully change the damage assessment, or is debris absence not a reliable indicator at this stage?

Shop is recommending a full engine rebuild at $30k. Before I commit to that:

1. Has anyone seen timing jump like this - both banks, opposite directions - after an in-car retime? Was retiming in-car even the right call on the M96? Any gotchas with that approach that could explain an immediate re-jump?
2. Can these sensor readings be trusted? Any known failure modes on cam or crank position sensors that could produce false deviation numbers of this magnitude? Worth ruling out before authorizing major work.
3. The car ran fine before I touched it. Previous owner drove it hard for an unknown period of time at those original deviation values with no issues. Does that tell us anything about how much damage has actually occurred, or is that just luck?
4. Drive home was under 6k RPM. Does that meaningfully reduce the risk of valve/piston contact from a jumped chain, or is it still a coin flip regardless of RPM?
5. Is a $30k rebuild warranted or is a targeted chain/tensioner/guides job still viable? Worth getting a second opinion or do these numbers tell the whole story?
6. Trailer or drive to a second opinion shop?

Assuming a borescope through the plug holes is the standard first step before anyone opens the engine - is that right or is there a better way to assess damage scope before committing?

I’ve been chasing a rough idle and hard restart issue on my ‘99 996 C4 and finally got a Durametric kit to do some proper digging. Found more than I bargained for and would love some input from people who’ve been down this road.

Background

Recently got my car back after a bunch of work was done at a Porsche specialist: front CV axle boots and axle seals, IMS bearing (SKF dual row) + TuneRS Direct Oil Feed kit, clutch (Sachs) + Dual Mass Flywheel (Luk OEM), transmission mount bushing, and a brake bleed. I’ve had this rough idle since I bought the car, and the Porsche specialist didn’t make any notes on it.

The Symptoms

1.	Rough idle / stall when parked nose-up on a hill with a full tank. Moving off the hill or dropping the fuel level resolves it temporarily. Disconnecting the battery also temporarily fixes it, which I think means the ECU fuel trim tables are being reset rather than the underlying problem being solved.  
2.	Hard restart after driving - happens after both spirited and normal driving. Shut the car off, let it sit, and it struggles to fire back up.

What Durametric Found

Fault codes: P0446 (shutoff valve activated charcoal filter), P0455 (tank vent system major leak), P1128 (O2 sensing adaptation idle range bank 1), P1130 (O2 sensing adaptation idle range bank 2), P1118 (heating power O2S behind cat bank 2), P0159 (sensor ageing behind cat conv cylinder 4-6), P1576 (cruise control readiness via CAN exceeds limit).

Camshaft deviation at idle: Bank 1 = -11.48° (spec is +/-6°), Bank 2 = -4.14° (within range). The Bank 1 reading is rock solid and non-fluctuating. I’ve also had a cold start rattle that goes away once the engine warms up.

My Current Theory

The P0446 and P0455 codes seem to confirm an EVAP system problem, which I think explains the rough idle and hard restart symptoms. Fuel vapor getting into the intake under high vapor pressure conditions like a full tank on an incline or a hot soak after driving.

The cam deviation is the reading that worries me more. From what I’ve read, -11.48° on Bank 1 combined with a cold start rattle points pretty strongly toward a worn cam chain tensioner and/or stretched timing chain on Bank 1. The cam tensioner gasket seals were replaced during the IMS job but the tensioners themselves weren’t accessed since they’re on the opposite end of the engine.

For the EVAP side I’ve identified the Bosch Regeneration Valve (996-110-129-53, ~$50 from Pelican), the Pierburg Canister Purge Valve (996-605-201-01, ~$191 from Pelican), and a fuel filler vent valve with P/N still TBC.

Questions for the Community

1.	Does the -11.48° Bank 1 deviation + cold start rattle = worn tensioner in your experience? Or could it be something else?  
2.	Any experience with the Bank 1 cam chain tensioner replacement on a ’99 996? What did it run you?  
3.	Does the EVAP parts list look right for the stall-on-a-hill + hot soak symptoms?  
4.	Should I be worried about the charcoal canister itself given the P0455 major leak code, or just start with the valves?

Happy to share Durametric screenshots if helpful. Thanks in advance!