96 S1 slow return to idle problem

Purchased new, 1996, SW1, 5sp manual, 310000km.
no ses light (previous intermittent ses light problems solved by changing
fuel cap)

Car starts and runs fine, no other problems noticed. Fuel consumption rate
may? be very slightly increased (not obviously excessive) but it is hard to
tell as consumption is usually slightly higher in winter.

At start-up, the engine initially runs at ~15-1700 rpm for 10-20 seconds
before reducing to regular idle speed.

When car is stopped, and engine is warm, if engine speed is increased to
+2000 rpm and then throttle is closed, the engine is slow to return to
regular idle speed.

Throttle linkage and return springs checked, OK.

I have never used intake or injector cleaners and have never needed to work
on intake or fuel system other than fuel and air filter changes.

Could this be a dribbling or leaking fuel injector? Warm engine idle is
smooth.

TIA

 

I would suspect a bad coolant temperature sensor (CTS). This is a $10 part
and 5 minutes effort to change it.

Bob

 

Bob, Thanks for this suggestion, I had forgotten that replacing the CTS
seems to solve most similar problems reported here.
See my later post in new thread Re: SL2 sticky throttle problem