Hi,

I have a rather odd problem with my '88 420SEL. The car runs fine when cold, up untill the tempurature reaches about 50 degrees Celcius. Then it abruptly slows down starting at about 1500 rpm, then accelerates . This "slowdown and go" repeates untill I increase the rpm above 2500 . As if the brakes engage and disengage. Once the temperature reaches above 80, everything is fine again.

- Fuel filter new
- Added Sea Foam to gas tank few weeks ago.
- Engine temp sensors test ok.
- Distributor and cap are new.
- Air filter new.
- Spark Plugs new
- Added Sea Foam in the tank few weeks ago.
- I have also Seafoamed the engine through Intake Manifold few weeks ago.

Can defective Thermo Vacuum valve cause this kind of problems? I have not tested them yet.

Thanks for any help.

__________________
Zorin

'88 Benz 420 SEL
'79 Porsche 911SC ('87 Carrera Engine)
'00 BMW 540 Sports Package
'99 Land Rover Discovery

86 300E - Manual (sold)
88 260E (sold)
84 944 (sold)