I'm having a problem with my RPM.
Everything is OK while driving, acceleration is good and no problems. except when I want to stop, the RPM goes down quickly to 500-450 and then goes up to 900 then back to good 800-850. some times it goes off especially when the air conditioner is working!
In general the RPM goes down to 500 and fluctuates back and forth to become stable after seconds.
1- I changed the stepper 3 times!, nothing happened.
2- checked the ECU and no faults detected, numbers were OK. I even changed the ecu several times with no changes!
3- Throttle intake is clean.
4- after warming up the engine, if I disconnect stepper cable the engine becomes stable and fine.
5- after disconnecting stepper the ecu reads no faults on (PP2000) and this was tested on three different ecu's.
Technician claimed that sensors are good.
In general RPM does not go up high numbers, it only goes down 500 and back to 1100 max then it starts to stabilize at 800.
NOTE: car was 405 1.6L engine, I swapped engine with Citroen Xantia 2.0L XU10J4R one, I faced this problem after swapping. After discussing this matter with others, it seemed a common problem after upgrading!. Same problem keeps happening to others not only me!
One claimed it could be related to brake system differences (ABS system and normal) and the brake pump could be sucking much air from intake manifold and that could confuse the ecu!
Is it possible? has any body experienced this problem before?