Rough Idle on start after engine is warm

[mgroth]

2000 Boxster S Manual
71k miles

Car starts fine when engine is cold and it idles normally. But after I drive it 15-20 min and turn off engine, it idles rough when I start again. If I do nothing, then engine dies after 5 seconds. But if I rev the engine for 5 seconds a few times then idle will settle on normal approx 700-800 RPMs and then be fine.

Engine Air filter is new and no CEL error codes.

I cleaned throttle body and air intake. was not very dirty. Only a little oil in the 2 big pipes.

Outdoor temp is 40-60F.

Any ideas?

Mike

[Gelbster]

Originally Posted by mgroth

2000 Boxster S Manual
71k miles

Car starts fine when engine is cold and it idles normally. But after I drive it 15-20 min and turn off engine, it idles rough when I start again. If I do nothing, then engine dies after 5 seconds. But if I rev the engine for 5 seconds a few times then idle will settle on normal approx 700-800 RPMs and then be fine.

Something is sticking? Because the revving that prevents the problem ,opens /activates something ? flap/butterfly /airflow ???

[particlewave]

Hard start when hot is typically EVAP related. Any codes?

Search "hard start when hot".

[mgroth]

Thanks for suggestions.

To clarify. It does not have hard time starting when warm, but the RPM needle does not settle at 700-800 but instead dances around and eventually the engine dies, UNLESS I rev it a few times, then it mellows out and is idling as it should.

[mgroth]

Thanks for the suggestions.

To clarify. It does not have hard time starting when warm, but the RPM needle does not settle at 700-800 but instead dances around and eventually the engine dies, UNLESS I rev it a few times, then it mellows out and is idling as it should.

[AZ986S]

Vacuum leak or O2 sensors.

[Gelbster]

Originally Posted by AZ986S

Vacuum leak or O2 sensors.

If it was o2 sensors a code would be at least Pending if not set. If it was vacuum leak(s) maybe ?
Eventually someone will mention the speed ,accuracy and ease of connecting a Durametric or PIWIS for a diagnostic fee. Meanwhile we can drag this out with speculation.It will be fun to see who made the best guess.

[Lapister]

I'm assuming you took off the TB and you cleaned both sides of the butterfly valve? First time I performed the service it ran rough too. Found the TB connector slightly loose ( not making). The point I'm really trying to make here is some people clean just the outside area of the TB and when they go to start the car it runs even rougher cause all the gummy deposits are suspended on the inside of the butterfly valve and feathering the slightly open valve reducing a smooth flow of air.

[mgroth]

Originally Posted by Lapister

I'm assuming you took off the TB and you cleaned both sides of the butterfly valve? First time I performed the service it ran rough too. Found the TB connector slightly loose ( not making). The point I'm really trying to make here is some people clean just the outside area of the TB and when they go to start the car it runs even rougher cause all the gummy deposits are suspended on the inside of the butterfly valve and feathering the slightly open valve reducing a smooth flow of air.

I did clean butterfly on TB . However I did not clean the second butterfly in the cross pipe near evap purge valve.

[mgroth]

I put in a new MAF sensor and problem went away.

My original MAF started throwing codes a yr ago. I cleaned it and that worked for a while. Then after a while codes came back. So I bought a new eBay MAF (Chinese) . Worked great for a while. On a hunch I installed the old one last week and the rough idle on warm start was gone. But CEL was back. so I just bought yet another MAF, this time a Bosch. I cleared CEL code and idles fine now.

Thanks for all suggestions and input.

[Gelbster]

So we all failed !Nobody diagnosed MAF
I am puzzled by the solution. In theory you could have just disconnected the MAF and the default would have produced reasonable performance and idle.
What gave you the idea to replace the MAF ?
Thanks for the warning about cheapo EBay MAF being short-lived !!!

[mgroth]

Originally Posted by Gelbster

So we all failed !Nobody diagnosed MAF
I am puzzled by the solution. In theory you could have just disconnected the MAF and the default would have produced reasonable performance and idle.
What gave you the idea to replace the MAF ?

Porsche friend said he had similar issue on his Audi and MAF was the issue.