Dr-18: No Fault Code Mechanical Test
At this point in the driveability test procedure, you have determined that all of the electronic control systems are operating as they were designed to. Therefore, they are not the cause of the driveability problem.
The following additional items can not be overlooked as possible causes of a driveability problem.
- THROTTLE VALVE AREA
Dirt or ice buildup causing rough idle and stalling. - ENIGNE IGNITION TIMING
Must be set with timing terminal grounded. - ENGINE VACUUM
Must be normal for your altitude. - ENGINE VALVE TIMING
To specifications. - ENGINE COMPRESSION
To specifications. - ENGINE P.C.V. SYSTEM
Must flow freely. - ENGINE EXHAUST SYSTEM
Must be free of any restrictions. - POWER BRAKE BOOSTER
No internal vacuum leaks. - TORQUE CONVERTER CONDITION
May cause very low power at breakaway or high speed (only 1 condition at a time). - FUEL CONTAMINATION
High alcohol or water content. - FUEL INJECTORS
Rough idle may be caused by injector wiring not connected to correct injector. - ENGINE SECONDARY IGNITION CHECK
Any abnormal scope pattern. - TECHNICAL SERVICE BULLETINS
Any that may apply to vehicle. - HOSES AND FILTERS
All air intake piping and vacuum hoses must be in place and secure. The proper air filter element must be used. - Must be correct specification with no vacuum at the regulator:
- 48 PSI on V6 & Non-Turbo 4-Cylinder
- 36 PSI on Turbo engines.
- COLD FAST IDLE AIR VALVE
V6 and DOHC engines: Coolant must circulate through this valve (mounted on the throttle body).NOTE: Any one or more of these items can give a driveability related problem. They can not be overlooked as possible causes.