Clever_User_Name

A little background first...

Bought my '01 Tip in early June. Got Kevin's flash about 2 months ago. Within a week, I threw misfire CELs. Turns out the extra juice was exposing old spark plug incapabilities. Replaced the spark plugs and ignition coil packs (since I was in there already). Worked like a charm after that - no CELs, no bucking.

Fast forward a few weeks...

Accelerating on an off ramp, engine dies on me. Dash lights up like a Christmas tree. Still have juice, just no engine. Have it towed to my mechanic, where he diagnoses a failed fuel pump. Replaces the fuel pump and, voila!, I'm back to running.

Fast forward two weeks...

On cold starts, I'm experiencing a peculiar behavior. I crank the car, it turns over, but idles rougher than usual and has zero throttle response. It only idles. I turn it off, crank again, and it works. May take one or two attempts, but it would work. No issues at all on a restart/warm start. Mechanic suggests the drive-by-wire is acting up and may need to be "reset". I do the reset sequence - doesn't seem to do anything. Over the next week, it seems to be getting progressively more difficult to start without that strange behavior. This Monday it took 5 attempts. Today, won't turn over at all.

Battery is a tad old, but given the cranking, figured that wasn't likely the problem. I hear the fuel pump priming when I turn the key. I haven't had a chance yet to check all of the fuses or tried disconnecting the negative cable to "reboot" the system. And not sure how to check relays (ignition, DME, etc.) if that is also something I should do. Read someone else's thread that his immobilizer was acting up - but wonder if my earlier starting problems have anything to do with that. I have a second key, which I haven't tried yet (was in too much of a rush this morning - so took the other car).

Sorry for the long post - but I wanted to offer what I know to be helpful.

Any ideas?

Kevinmacd

Need to get it on a Durametric and look at what's happening

Clever_User_Name

So tonight I get home and try to start it. Turns over, after 1-2 seconds, rpms drop to 700 and car stalls out after a few seconds. And definitely running rich. Smells so.

Hook up the duranetric and reads a P0102/115 hit film MAF sensor. Oddly, it disappears when I run a second check.

Should I replace the MAF sensor?

Macster

Not right away. The MAF is rather expensive and if your diagnosis is wrong...

Under P0115 I read: engine temperature -- signal implausible.

It is not clear to me based on my resources if the intake air temperature sensor (part of the MAF's function) is being referred to by this error code or if there's some other temp sensor. I know it is not the engine compartment sensor so that leaves the coolant temperature sensor.

But a note reads: A thermostat that is constantly open can cause the fault.

And the list of possible fault causes, there's Thermostat (permanently open); open coolant shutoff valve (Tip vehicles only); wiring; temperature sensor faulty; DME control module faulty.

In other places for other errors, for instance P0507 (idle air control at stop -- above limit) both engine temperature and intake air temperature are listed individually, so I'm thinking 'engine temperature' is really the coolant temperature.

The error might arise because the coolant temp and the intake air temp differ by too much but the DME can't know which one to believe and which one is bad.

Use the Durametric tool to view/monitor both intake air temp and coolant temp at all times and see if any reads wrong. At cold start both should be close to ambient.

Sincerely,

Macster.

adam_

I'd check and clean the contacts to the MAF. As I recall the maf also has a temp sensor in it.

bogotajoe

My 02 TT has 18K miles on it. I was looking into a flash and was strongly advised to change plugs, coils, MAF and the 2 pre-cat O2 sensors prior to doing the flash.

Macster

If the company offering the flash advises that then you should do it.

After all you are relying upon the company to supply the most critical portion of the car's engine electronics: The engine controller's firmware. IOWs the software that runs in the engine controller microprocessor and is responsible for managing/controlling everything regarding the engine, like when to trigger the spark, when to inject fuel and for how long, when to advance, retard, or change the lift of the intake valves and so on.

If you can't trust the company regarding what it feels is appropriate to do prior to installing the flash then I can't see how you can trust the company at all.

With a flash the engine is being asked, forced, to make more power. This puts more stress on the various components mentioned above save perhaps the MAF.

Actually I take that back. Even the MAF since to make more power the engine will flow more air and the MAF will have to measure this greater flow or mass of air and react quicker because the engine is doing more in the same amount of time.

Plugs of course play a critical role in combustion and guess what sparks the spark plugs? The coils.

The two pre-cat O2 sensors are wide band and are used to control the air/fuel mixture being fed to the engine. Wide band sensors are used to more precisely control this mixture. The NA engines use plain old narrow band sensors.

Anyhow, since the engine is being forced to generate more power there is less margin for error for this mixture to be wrong or not as right as it should be.

The sensors need to to be fresh to be at their top condition.

Furthermore, the 02 sensors along with the plugs and coils too will almost certainly have to be replaced more often since they will degrade. This degradation is not a problem (well, until it becomes a problem) for stock engines but your engine with the flash will no longer be stock even though you've never opened it up.

Also, oil/filter services (at least) should be done more often. You should consider following a shorter oil change service schedule simply to provide that extra margin of protection to the engine since it will be working harder -- at least some of the time -- with that flash in it.

Sincerely,

Macster.

adam_

^^^ Is this a philosophical commentary or is this responsive to the OPs issue????

Macster

It was a response to the query from Bogotajoe.

Sincerely,

Macster.

Kevin

This is a AWESOME thread.. Perfect timing for a few folks.

I do question if your fuel issue has been resolved. Did the tech remove and replace the two Venturi lift pumps (guys these are failing) When you replace the fuel pump you really need to replace these lift pumps. I have found that the running stalling issues "point" towards the fuel delivery system, this includes the venturi lift pumps. You are using fuel from the electric VDO fuel pump to create suction to remove the fuel at the bottom two fuel pods. To do the diagnostics, what is the fuel level in the tank. Are all these stall issues coming at below a 1/2 a tank of fuel.. If it is>> order up the two lift pumps.

Adam will usually offer the advice to disconnect the MAF sensor wiring harness connection to see how the car will run. If the car has 50K or greater on the Wideband pre CAT O2 sensors replace them.

Kevin

I didn't catch READ that you tripped a code. This is the Porsche DME info that I have.. I'd replace the MAF anyway, but you can check the connection AND disconnect the MAF to see if the CAR runs better.

P0102
115 Mass air flow sensor – below limit
Diagnosis conditions
• Engine running
• Battery voltage greater than 8 V
Possible fault cause
♦ Open circuit
♦ Short circuit to ground
♦ Mass air flow sensor faulty
In the case of a fault, the PSM is switched off.
Affected terminals
Terminal III/23
Diagnosis/troubleshooting

Clever_User_Name

Update is this: Mechanic gets the car and can immediately see exactly what is happening. They run a number of diagnostics, test just about everything. Even went old school with actual tools to find what is wrong. Completely perplexed. Does a throttle body adjustment. Car runs fine. Like nothing was ever wrong.

Go figure.

Clever_User_Name

Kevin,

Quite by accident, I happened across this very helpful thread concerning failed venturi tubes which seems to describe my exact issue.

https://rennlist.com/forums/996-foru...t-start-5.html

Interestingly, towards the end of that thread, someone also describes an issue fueling the car. I have the exact same issue. I'd bet $500 that the venturi tubes are obstructing the flow of my bladder (I like the zip tie TSB fix ). Now I have to wonder if my problems starting the car were also when the tank was below half full - suggesting one of the tubes was malfunctioning.

Either way, happy I am up and running (for now), but definitely have to look into the potential tube obstruction problem.