1982 500SL - low power

Hi all. My 1982 500SL seems to exhibit a strange behavior and I'm wondering if anyone else has ever experienced it. If I drive the car for a little while, and then turn it off for a few and start it back up
again, the car seems to have virtually no power. I can floor the gas pedal but the car will accelerate very slowly. Sometimes, this problem will go away after several minutes of driving. I just had the vacuum modulator and the hose going to it replaced on the transmission thinking that would solve the problem and it hasn't. Both were cracked. Anyone ever have this happen? It only seems to do it if I shut the car off after driving it a little bit and start it back up again. I live in the US if that makes a difference; this car is grey market. Any suggestions would be appreciated. Thanks!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Pull the plugs and have a look at them. it could be that one or more of the plugs is getting oil fouled... Then when you restart the car, you have none of the advantages and a cold start (ie moree fuel and higher idle speed), so you are noticing the engine misfiring. Once the plug heats up enough to start firing properly, it runs smoothly again.
Just a theory, but a relatively simple one to test.
Marty
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It does idle a little high, maybe around 900rpm. I'll have a look at the plugs for a start. I can't say that I've noticed any misfiring though.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This is nothing more than a stab at your car's problem, especially since it's a gray market vehicle.
I suspect the engine's control computer is misreading either the engine's temperature or the O2 in the exhaust or throttle position but, as I wrote, its only a stab at the problem. This problem is engine control related, not just a simple vacuum leak.
It's OK if you start it cold and drive continuously for a long distance but NOT if you stop for gas etc. and then restart it.
This won't be easily found. If the engine is not hot BUT the computer believes it IS hot then a lean air/ fuel ratio will be put into the engine. A faulty temperature sensor might be the cause. Or a bad O2 sensor.
The throttle position sensor is less of a suspect as the problem only occurs during warm up.
You won't solve this so find a shop that understands the difference(s) between the USA spec and gray market spec cars.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I was looking for vacuum leaks yesterday and came up with nothing. I did discover that one of the wires to the cold start valve wasn't connected very well. But, I don't think that was the problem though. I'll replace the O2 sensor since I have no idea when it was last changed. I'll also try disconnecting the temp sensor while the car is idling to see if anything happens. If I remember correctly from my Volkswagen, if you disconnect the temp sensor and nothing happens to the idle, then it isn't working. I could be thinking of something else though.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.