1997 boxster warm start problem

[STYLUS]

New to this site hoping to find help with a very frustrating no start w/ warm problem. Any information, or ideas will be much appreciated.
Events of the past 3 weeks:
1) i replaced water pump 3 weeks ago. Took all steps to restore cooling system. Cools perfect (185). But, left damaged plastic shield off to replace later.

2) boxster ran perfect. Then, last week would crank and not start. Restarted and ran fine after cooled for 45 min. Since then this problem is predictable.

3) first start. Boxster always starts and runs perfect. After reaching operating temp, it will turn over but will not start. After 45 min or so, it will start and run fine. Have noted that if the engine is not cooled down enough (30 min or so) it will start but run rough w/ a slight mis firing feel and sound. Will run if it stays running at high rpm for a min or so, then it will run fine. Again, when engine is turned off after a short run, it will start perfect but after it sits for 15 min, will not start until cooled (45 min or so).

4) slight fuel smell after restart problem at traffic light.

5) code at independent shop today po102 mass flow sensor low input.
Recommended replacing crank angle sensor/mass air flow sensor.

Wondering which sensor that i should replace first with the clues above?
Also, 08/08 previous owner had boxster scoped w/porsche pst2. Results were fault code 02 sensor cyl 4-6, 02 range cyl 1-3. Do not think that this work was done. And, would this cause a no warm start problem?

With the mis fire sound when first starting after a cool down period, would a mass flow sensor be the first to replace? Would a crank angle sensor act this way after a cool down start?

Any help, or ideas will be much appreciated as i am loosing sleep on this one...hard to figure.

Will a porsche pst2 zero in on a crank/air flow sensor problem? Piwis? Thinking i need at least a durametric???

[Paul]

I would do some trouble shooting while it is in the will not start mode:

Check for spark

Check fuel pressure

Also pull the connectors off the MAF and crank sensor and reseat.

Has your coolant level been dropping?

Any soot in your exhaust tips?

[STYLUS]

thanks paul. will check it out, and post results. also, wonder if the low idle sensor could create this problem? coolant level is stable.

[thstone]

"code at independent shop today po102 mass flow sensor low input"

I'd suggest to start by replacing the MAF. First, that is what the fault code identifies; Second, that is what your indy shop recommended.

Yes, the fault can sometimes be caused by another component not flagged by the computer but unless you have strong reason to suspect something else your best bet is to start with the somewhat obvious.

[Paul]

This could be the age old problem of the fuel vaporizing in the lines due to excessive heat on the fuel system or the lack of the fuel injection system maintaining pressure after shutdown.

Again check the fuel pressure while it is in a non start condition.

[STYLUS]

Paul. Thanks for the information. Do you know what psi is normal? And where the best place to take the psi would be if the fuel is vapor locking ? Also, i read that the fuel pump normally does not run until the engine is running, and not in the key on position.

[Paul]

There's a port on the fuel rail. If there is no pressure, check the fuel pump relay first.