W126- Loss of performance upon warm up

[Snowman]

1985 500SEL, 130k miles

I've noticed that the car performs the way it should when it's slightly cold. Once it warms up, it still goes but not the way it did before. In other words, the car is slower once the engine gets up to temp. So any ideas on this?

[fahrgewehr2]

You probably have a problem with the electronic control of your fuel injection system. Dont think pre-85 cars have an EHA or potentiometer, but they should have an 02 sensor if a US car.

Read up on 'closed loop' 'mixture' and o2 sensors.

Basically, your engine experiences cold start enrichment and at around 60degC, begins to switch over to closed loop operation, where the electronic potion of the FI system begins to have influence on mixture.

Now, I have found that these CIS cars are a little quicker when you first start them up cold in the morning. I Attribute this to colder air being ingested, along with more fuel being pumped into the engine, hence, more power. Just my idea though.

Good luck.

If there are mistakes in my explaination of the system, someone please correct.