Hello. I have a 1967 420 TS (Touring Sedan) not a 420 G. Since I bought the car back in 2014, when the engine gets hot and when standing still at a stop light or in heavy traffic, the tachometer will "wobble" between 600 and 750 RPM. When this happens, the engine seems to shake and I sit in the car and can feel it "vibrating" through the body. If I take the car out of gear into Neutral or Park the engine revs go up to around 900 RPM and is as smooth as can be. When cold, the idle RPM is around 1000 with the choke engaged and after a minute and half it drops to around 650 - 700 RPM.
The car rides really well other than this little annoying wobble. I just had a complete valve job done on the car as there was no compression on #1 cylinder. I had hoped that this would cure the drop in revs but it didn't. May I ask if anyone else has experienced this and what they did to cure it?
If it was a vacuum leak, wouldn't it happen even when cold?
Many thanks in advance and all the best.

 

We would suggest you look at your transmission functions and cabling to the carbs from the transmission.

 

:-) That is Greek to me but when I get the car back to CT I will have a mechanic look at those items. Many thanks for your help.
Chris