You have taken your car to a few mechanic and they still cannot find the vacuum hose! or they cannot find the leak at the vaccum hose?
Vacuum hose are relatively cheap. If you car is about 6 years old, it would be advisable to change all the rubber hose as a routine maintenance. This include all the water hose from radiator to engine bay etc.
When you say that you replace all ignition coils, what do you means? Your car got more than 1 ignition coils?
Engine misfiring can be caused by :-
1. spark plugs
2. loose ignition cable ( you can check this by removing one cable at a time. The cable that does not retart the engine speed is the cause)
3. faulty ignition cable (high tention cable). Leak of high tension voltage to ground. (use a long expose screwdriver and lay it along the cable. If there is small spark, then the cable is faulty)
4. air filter complete choked.
5. faulty TPS (throttle position sensor)
6. fault MAF.
7. knock or camshaft sensor
8. choke fuel injectors
I would check the spark plugs first. then air filter. then ignition high tension cable. then change vacuum hose. then check TPS. then MAF..
btw, item 1, 2 & 3 fault cannot be find by GTII lah..
