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post #1 of 5 (permalink) Old 02-13-2011, 07:43 PM Thread Starter
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Angry Rough idle: Brake Booster

My rough idle, almost stalling then recovering was caused by the Vaccuum Brake Booster. 2006 mazda 6 3.0 ltr automatic. Symptoms: after 15-25 secs at a stop light, the idle would drop down 75-100 rpm (650-675ish), I would feel weird vibrations and different sound in the exhaust. Then it would really drop for a split second and then recover. After 5-10 times the check engine light would come on. It would run good but lack a little low end power otherwise. Kept on getting codes: P0131, P0151, P2187, P2189. Basically lean @ idle, lean bank 1 or 2. I changed PCV valve, cleaned the throttle body, changed the purge solenoid valve, inspected the PCV hose (notorious for cracking), checked for vaccuum and intake leaks. I had maybe 43,000 km on the car. I was told to change the sensors. I put on all 4 NTK sensors. Still no change. I finished doing the Y-Pipe (Stock is very bad). I changed the mass air sensor. I put the stock intake back on (removed the bottom plate and drilled holes in bottom of silencer to get at cold air). I installed a new vaccuum solenoid at intake flapper. I removed my ground wires for a week. Still no change. Electrical harness inspected along with my aftermarket O2 sensors: Passed. They could not figure it out. The dealer told me I had to put Mazda sensors back in. The dealer also told me I had to put the factory stereo back in and change back my Y-Pipe (before a computer could be authorized). They were idiots. I had them check EGR valve and spray cleaner in it. I did EGR mod. I sprayed Ether around everything with no change. I took it to another dealer. They found the O2 sensors would shut-off by 4's or 2's for a split second sending fuel trim all over the place. They changed the computer (no issues with stereo, ground wires or Y-Pipe). Still acted up. Finally he checked the brake booster and discovered that when the vaccuum line was pinched it would run smoothly. We got one from the bone yard and now it is fine. Been driving for 2 weeks with no issues. I also told the first dealer to check the brake booster because I had also issues with poor stopping a few odd times (he obviously did not check it). To re-iterate, this issue came @ idle while my foot was on the brake pedal and car was warmed up. Sometimes you have to be really descriptive when things are happening. I don't think the first dealer warmed up car properly (because I never heard them rev it up like the second dealer).

Last edited by BigAlDJ; 03-21-2011 at 05:16 PM. Reason: ...
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post #2 of 5 (permalink) Old 02-14-2011, 06:11 PM Thread Starter
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Bottom Line. A lean @ idle or lean bank condition is normally caused by a vaccuum leak. The mass air sensor is not reading all 100% of the air going in because extra air is going in from somewhere else. In this case it was the Vaccuum Brake Booster assembly.
The mechanic said the last time he changed one was 1979.
Check all vaccuum and intake possibilities before changing O2 sensor. Including the accordian intake tube before the throttle body---it cracks as well.

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post #3 of 5 (permalink) Old 02-16-2011, 01:05 AM
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Good to know what to look out for when problems come up.

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post #4 of 5 (permalink) Old 03-21-2011, 04:43 PM
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Quote:
Originally Posted by BigAlDJ View Post
My rough idle, almost stalling then recovering was caused by the Vaccuum Brake Booster. 2006 mazda 6 3.0 ltr automatic. Symptoms: after 15-25 secs at a stop light, the idle would drop down 75-100 rpm (650-675ish), I would feel weird vibrations and different sound in the exhaust. Then it would really drop for a split second and then recover. After 5-10 times the check engine light would come on. It would run good but lack a little low end power otherwise. Kept on getting codes: P0131, P0151, P2187, P2189. Basically lean @ idle, lean bank 1 or 2. I changed PCV valve, cleaned the throttle body, changed the purge solenoid valve, inspected the PCV hose (notorious for cracking), checked for vaccuum and intake leaks. I had maybe 43,000 km on the car. I was told to change the sensors. I put on all 4 NTK sensors. Still no change. I finished doing the Y-Pipe (Stock is very bad). I changed the mass air sensor. I put the stock intake back on (removed the bottom plate and drilled holes in bottom of silencer to get at cold air). I installed a new vaccuum solenoid at intake flapper. I removed my ground wires for a week. Still no change. Electrical harness inspected along with my aftermarket O2 sensors: Passed. They could not figure it out. The dealer told me I had to put Mazda sensors back in. The dealer also told me I had to put the factory stereo back in and change back my Y-Pipe (before a computer could be authorized). They were idiots. I had them check EGR valve and spray cleaner in it. I did EGR mod. I sprayed Ether around everything with no change. I took it to another dealer. They found the O2 sensors would shut-off by 4's or 2's for a split second sending fuel trim all over the place. They changed the computer (no issues with stereo, ground wires or Y-Pipe). Still acted up. Finally he checked the brake booster and discovered that when the vaccuum line was pinched it would run smoothly. We got one from the bone yard and now it is fine. Been driving for 2 weeks with no issues. I also told the first dealer to check the brake booster because I had also issues with poor stopping a few odd times (he obviously did not check it). To re-iterate, this issue came @ idle while my foot was on the brake pedal and car was warmed up. Sometimes you have to be really descriptive when things are happening. I don't think the first dealer warmed up car properly (because I never heard them rev it up like the second dealer).
Can you show a pic of the brake booster line he pinched? also how hard was the booster to get to? Mine was doing the same thing with a aftermarket intake... but mine is manual and would do it worst when the AC was on...

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post #5 of 5 (permalink) Old 03-21-2011, 05:16 PM Thread Starter
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I have no idea. It was done at the dealer.
It is hard to get to. It was a 3 hour job.
Did you plug the vaccuum line that originally went to stock airbox?
Mine came with a fancy short hose/plug. You could plug it off with a screw & clamp.
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