Hey,
I just went through this on my 85. My car is a low mile car but very neglected by the po. I solved my low power issues over the last couple of months.
Here is what I did in chronological order. It seemed that it wasn’t one thing that was messed up. There were lots of little issues robbing power at different rpm and load ranges tha needed to be fixed.
I checked and adjusted valves like you. This cleaned up the idle and got some power back. I adjusted the accelerator linkages and set the idle. No big improvement there. I adjusted the rack damper bolt and smoothed the engine out but that didn’t do much. The bolt was pretty much bottomed out by then.
I opened the turbo on the intake side by just taking off the rubber boot. Checked to see that the turbo spun freely (with the car off
). It was a bit sooted up and draggy so I sprayed it with carb clean and it loosened. I got some power back.
Checked the boost pressure at the ALDA under load. This will check the turbo banjo, switchover valve and lines all in one step. This is a common issue that will rob power. It was ok.
Changed an air filter. Bypassed the trap Catalyst which helped a lot. My cat was apparently restricting exhaust flow. But the car wasn’t 100% right at this point. Yes it made power but it wasn’t tractable power for around town driving. It was good wide open now.
The car now made power wide open but off the line it stuttered and just revved slowly.
I changed the fuel strainer and filter. And I changed to a cigar hose. The po used a regular fuel return hose. This helped the tip in power.
I turned my ALDA screw out 1/4 turn CCW. This helped. I started with 1/2 CCW but the exhaust seemed to laden with fuel and was nauseating. I gave up some power but it smells better now.
Then I decided to cut the locknut on my rack damper bolt down 0.060” and adjust it in a bit. This helped the shaking at tip in. Before this the car would shake as I pulled up and down my driveway. It struggled at low throttle position maneuvers. I mean I couldn’t floor it to make power to climb my sloped driveway to my garage door. Once I got the bolt screwed in enough it could heft its mass smoothly with ease and control. Before this point the pedal had to settings, up and floored.
With all those little things the car is now making good smooth power. I cannot say it was any one thing that fixed the power. Many problems contributed to the power loss so I had to undo them one at a time.
I’ve discussed the car a lot in my Got a 1985 300d thread. It was severely neglected. Basically the MO of the PO was if something broke, just keep driving. So eventually nothing worked and the car got parked and left for dead. Thankfully it had a good chassis, engine and trans. So I’ve spent two months fixing little things and gradually getting this thing drivable.
Put it all together and the car runs beautiful now. I’m still scratching my head thinking that it wasn’t just one thing. It was like four things that just weren’t right.
Hope that helps.