Annoying cold start problem on a 1997 2.5 Boxster
 

Good Day all,

Since a few months my 1997 2.5l Boxster is having cold start issues which are slowly getting worse.

The engine stalls immediately on a cold start - or when I have attempted to start it several times, the idle starts hunting up and down until it slowly settles. Touching the gas pedal helps a bit as it warms up the engine quicker.

Things which are already done:
- Checked for codes - none found
- O2 sensors changed
- IMS changed
- Clutch changed
- Chain guides changed
- Camshaft deviation checked
- MAF changed
- Checked for vacuum leaks
- AOS changed
- Plugs + tubes changed

Once hot - car starts fine though performance doesn't seem optimal during driving.

https://youtu.be/aCvgvcqTgU8

I hope someone can help me out - getting quite tired of this. Please check the video for reference

I think you have a vacuum leak. Have the vacuum lines smoke tested.

1. How many miles on the car.????
2.hookup a scanner to the OBDII and look at coolant temp when dead cold,
before you try to start it.
What does it read????

A faulty Temp. sensor can show a false (warm) coolant temp when the engine is dead cold. The ECU thinks the engine is warm so it does not enrich the fuel (pulse injectors longer) for cold start.
Let us know what you find.

Did you install a Bosch MAF sensor ? Most of the other brands are inferior.

On top of everything else mentioned, clean the throttle body and check the idle control valve.

Sure sounds like a small vacuum leak, though.

Would like to mention that an original Bosch MAF has been installed, ICV checked and compared with another one, both working fine. TB cleaned several times

The car is in a shop now and they can confirm that fuel pressure is OK and coolant temp sensor is showing the correct figure when cold....

They say that they didn't find any air leaks, though I'd like to check this myself at home with my DIY smoke machine just to be sure..

This is probably irrelevant since it sounds like you have been dealing with it for awhile, but my 1999 Boxster had those exact same symptoms and also didn’t throw any codes. Turned out to be bad gas.
Once I flushed the tank out and filled up at a different place, it went back to normal immediately. Symptoms never returned.
Second guess would be the temp sensor. Wouldn’t be out of the question that the MAF sensor could be faulty even though you’ve replaced it.

Looks like it was the throttle position sensor (TPS) which was giving wrong values on the first percentages of throttle in combination with a loose AOS hose on the bottom.

This explains why after every reset the car ran more or less fine (default settings) - and became worse the more kilometers I made.

Idle hunts still a little bit on a cold start, but not stalling any more (hunting between 700-1100 RPM and quickly settling). Fuel trim on the long term is still a bit off, but becoming better the more I drive.

Bank 1 Long Term: -1.6%
Bank 2 Long Term: -4% (seems like something is not yet correct here)

I'll keep you posted,

Happy holidays.