1991 Mercedes 420 SEL - Idling Issues

[ron59b]

My 1991 420SEL has 178,000 miles. The timing chain failed at idle, damaging the top end. The engine was rebuilt and is now back together and running.

The current issue is that the car starts and runs well when cold. Once it reaches operating temperature and runs for a while, idle quality deteriorates, and the engine tends to stall. The problem worsens as the engine remains hot.

The shop disconnected the Idle Control Valve during diagnosis. When unplugged, the idle speed increased, and the engine ran much more smoothly.

Work completed:

* Top-end rebuild following timing chain failure
* New timing components installed
* Engine reassembled and timed

Things I am considering:

* Idle Control Valve failure when hot
* Vacuum leak
* Coolant temperature sensor
* Electronic Throttle Actuator (ETA)
* Engine wiring harness deterioration
* Fuel pressure issue
* Cam timing off by a tooth after rebuild

Has anyone experienced a similar warm idle problem on an M119 after major engine work? Any specific tests or common failure points I should investigate first?

Thanks in advance for any suggestions.

Thank you,
Ron

[Frank Reiner]

Please post pics of the car and the engine (with the air cleaner removed).

[porkface]

leaking injectors and/or fuel dist can also cause this.

[ron59b]

I can't get my pictures to post.

[ron59b]