w126 420SEL...rough while cold...out of ideas

[qwerty333]

Car has 335,000km and is a 1987 420SEL

I got it about 2 weeks ago and have been working on figuring out the roughness and general hesitation of the engine. It was really bad at first but still "driveable", however it felt like it was going to die at stop lights or while idling in drive. It was a bit smoother in park at higher rpm.

I replaced the following things in this order:
1. Spark plugs - no difference
2. Ignition wires - little bit of improvement
3. Cleaned corrosion from distributor cap and rotor - little bit of improvement
4. Removed all fuel injectors and took them for testing and cleaning...one was clogged but is now spraying correctly. Smoother idle after reinstalling them
5. Found 2 or 3 disconnected vacuum lines in the engine, connected them properly - Car idles 95% smooth and fires on all cylinders ONLY after driving for 10 min, parking the car, turning off the engine and restarting it. WTF
6. Cleaned idle air piston thing - Slight improvement at warm idle


When I cold start the car it will run like crap and the engine will run very cool no matter how you drive. It will stay under 80 degrees celsius the whole time and feels like 1 or 2 cylinders might be missing, but not misfiring out of time or anything. While this is happening, the transmission refuses to kickdown properly. 0-60mph time in this situation is around 11.5 seconds

After driving it around, and letting it idle a bit, if i turn off the car and let it sit for 2 minutes, then turn it back on, it will then fire on all cylinders and idle very smoothly. The temperature then goes to 90-100 degrees celsius. Kickdown works properly and the car has full power again. 0-60mph in this situation is 8.5 seconds.

I've run out of ideas for what may be causing this weird pattern.