1998 Boxster High Temp problem

[Leprechaun]

Looking for feedback from anyone who can help with this.

I have a problem That only manifests itself at high engine temps just before the car reaches the temp the radiator fan turns on to start cooling. The enigne starts to cough lik it's running out of gas. When come to a stop the idle RPMs fluctuate up and down between 900 and almost 0. Sometimes it stalls unless I pump the accelerator. The fault codes I see are that the fuel injector system seems to loose itself and change the air fuel mixture from lean to rich and then from rich to lean and finally seems to get lost and then I'm starting to think that it may be minor vapor locking when the engine gets hot which might be the cause of the air/fuel mixture fluctuations. It only coughs but never stalls when the car's moving. I have changed the MAF, Both Engine side O2 sensors and the relay that operate the Fuel Injection system. The car also recovers when the engine has cooled down and gone through it's warm up cycle and returned the air fuel mixture.I remember reading somewhere when I first got the car and vapor lock was mentioned but I can't find that article again. Has anyone heard about this and if you have, do you know what the solution might be?

[Dale_K]

What year is the car? Does it have a Tiptronic?

My car has a Tip and there is a vacuum operated coolant control valve that can create a vacuum leak if the valve is bad but only in high temp situations, when the car thinks the Tip needs more cooling.

I think vapor lock is less of a problem on cars with the pump inside the tank but I guess you could have a faulty fuel pump or fuel pressure regulator. You could buy a fuel pressure testing gauge and compare readings before and after the motor heats up. Different year cars have different fuel systems (two pipe, one pipe).