There is a TSB for manifold leak at the corner, have a look if this matches your problem.
ROUGH IDLE/HESITATION DURING ACCELERATION - MIL ON TECHNICAL SERVICE BULLETIN Reference Number(s): 015/00, Date of Issue: October 18, 2000 Related Ref Number(s): CAT. 01, NO. 015/00 ARTICLE BEGINNING ROUGH IDLE/HESITATION DURING ACCEL - MIL "ON" Model(s): 1998-01 Mazda 626 Category: 01 - Engine Bulletin No: 015/00 Date: October 18, 2000 APPLICABLE
MODEL(S)/VINS All 1998-01 4-cylinder 626 with VINs lower than 1YV GF22C4 15202676. DESCRIPTION The MIL may illuminate with DTCs P0171 or P0301-P0304 stored in memory. There may also be a concern of rough idle or hesitation on acceleration. These concerns can be caused by a vacuum leak at the intake manifold gasket. Customers having this concern should have their vehicle repaired using the following procedure.
REPAIR PROCEDURE 1. Verify customer concern. 2. Using the NGS Tester, retrieve any DTCs stored and record Freeze Frame Data. 3. Start the engine and select the Short Fuel Trim PID (SHRTFT1) and Long Fuel Trim PID (LONGFT1). 4. Using an aerosol spray such as carburetor cleaner, spray around the intake manifold gasket while watching for changes in idle speed or SHRTFT1 values. NOTE: High positive values (e.G. +12% or greater) for SHRTFT1 or LONGFT1 stored in Freeze Frame Data or seen in PID data may indicate that unmetered air is entering the engine through a vacuum leak at the intake manifold gasket. NOTE: Be sure to spray the gasket area under intake runners #1 and #4 cylinders.
Wednesday, July 23rd, 2008 AT 1:50 PM