Surging during decerelation , hot and rough Idle

I am using V 1.225 on both my computer and ECU (Classic).

When I am decelerating, the car surges strongly between 1750 to 1500 RPM. I am also having difficulty controlling the idle valve (Bosch 3 Wire without spring), and the car always overheats when idling.

In 1st, 2nd, and 3rd gear, without pushing the gas pedal, the car surges strongly between 1750 to 1500 RPM. When I press the gas pedal slightly, the surge goes back to normal.

This issue occurs regardless of whether the engine is hot or cold. There are no error messages or warning lights displayed.

I recently upgraded from Vipec V44 to Ecumaster Classic with a new harness. The radiator thermostat and water pump have been replaced, and the temperature sensor on the radiator (which controls the auxiliary electric fan for cooling) has been changed from 99 to 91 (first) and 92 to 86 (second) to kick up at lower ECT degrees.

The engine is a BMW M30B34 with a 10:1 CR, 284 Degree Schirick Cam, and a lightweight flywheel. The rest of the engine is standard.

It is a standalone ECU with a custom harness. The engine is original to the chassis of a 1986 E28M535i (Euro).

Any advice on idle and ignition would be greatly appreciated.

Surge you mean the car jerks back and forth ?

Thanks a lot for your reply. Yes, the car jerks back and forth.

I think I found the problem, but I don’t have a solution yet.

When I slow down without pressing the gas pedal, MAP drops to 19 kPa, depending on the engine load. Between 1850 and 1500 RPM, the jerking happens. When I decrease the VE from 56 to 20 between 2000 and 1250 RPM and between 38 Kpa to 20 kPa, the jerking stops, but then the idle starts to surge.

When I use fuel cut trim between 2000 and 1250 RPM, there’s still a jerk at 1250 RPM when the fuel comes back.