Surging idle 3.6 M104
 

Hi Everyone- I have a persistent problem that I can't seem to resolve. My 95 w124 wagon has a 3.6 m104 swapped into it. It uses the original w124 wiring harness and belt driven air pump. The car has a hunting idle when warm that I can't seem to fix.

So far, I have changed the plugs, coil packs, resonance valve, cleaned the injectors, coolant temp sensor, swapped O2 sensor, swapped MAF sensor. The car drives and runs great. There are no codes thrown at all. None of these things has materially changed the warm idle. Recently, I unplugged the air line on the EGR and the idle seemed to smooth out.

It seems backwards that the EGR would be at fault as there is no code and it is only when warm. What are the symptoms of having a blocked EGR tube? The throttle body has been replaced with a rebuilt one. We reused the gasket from the old one on the replacement. I now have a new throttle body gasket but have not got around to replacing it yet.

Does anyone have any suggestions here? Thanks in advance- Cory

I just wanted to add a couple things to the thread. The car has a replacement harness and rebuilt throttle actuator. I have a code reader and it is not throwing any codes that I know of.

The warm idles hunts up and down about 1-200 rpm. I suppose it would be termed more of a hunting idle.

Check the charging voltage. I've seen an overcharging alternator make the throttle actuator act nuts.

I need to check my alt too,I have same issuse.Also I heard a lower thermostat can do it also
Mine dissappears when fully warmed.