Slow down light

Did you make sure your thermocouple ECUs were hooked up to the right harnesses?
Is the cat material ok?
Do you have any codes?

 

So have you tried swapping over the 4 pin plugs on the Thermocouple ECUs?

The bypass ECU should have green, black and purple/black wires, although some cars have blue instead of purple/black

 

The three TCU are identical. You have a problem with the bypass circuit. Go find that.

1. Make sure the right thermal couple and the right signal connector are going to the right TCU on that rat's nest. Ian has you covered for that.
2. Make sure the bypass valve is working correctly. Use a hand pump to introduce vacuum to the line and observe that the bypass flap is opening at the right vacuum point.
3. Make sure the bypass valve is normally closed, not normally open (unless the electronic is also supplied to flip the logic, this sucks)
4. Make sure there is sufficient vacuum at the vacuum bottle in the right hand side corner of the car
5. And the vacuum switch is functional.

Beyond that, you have to worry about getting enough vacuum from the intake plenum. That is a well covered problem, previously solved somewhere.

 

There are two TCUs in the first photo. One is above the other. One of them is the bypass TCU. Which one it is, depends on which thermocouple is attached to it. These get swapped around more often than you can imagine. The physical location is not important as long as the correct plugs are attached to it. If you can't identify wire colours you can either 1) swap one of the plugs on the TCUs, clear the messages and go for a drive... or 2) do continuity checks between the TCU 4 pin plugs and the Motronic ECU.

 

My tech has similar experience and has done the same thing. It can happen to anyone.

 

Swap these plugs...

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Or the two pin plugs (going to the thermocouples) if they are easier to get to. Just don't swap all 4.

 

TCU swapped. It happened to me just once, the very first engine out. Never did that again, ever.
Water pump. This is very likely a bad water-pump rebuild during the engine out. I don't do rebuild anymore. New pump goes in, or old pump goes back in with zero warranty.

 

According to this graphic, the bypass TCU is the vertical one...

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Make sure the bypass thermocouple is attached to it, then work from there.