Engine shake at idle

[mediumchung]

Hello, I own a 2006 Mazda5 2.0 and the problem came since last week.
The engine shock slightly during idle when A/C was off, and shock like going to stall when the A/C was on.
When I pressed on the pedal the vibration simply gone. It ran smooth like usual but gas consumption increased by 1/4.
The RPM at idle was normal at around 700 - 800 when the engine shock. The check engine light was not on.

I have replaced all 4 spark plugs, replaced a faulty ignition coil, oil changed and cleaned the throttle body just 3 months ago.
I believed that the A/C compressor didn't run smooth so I replaced it today, but didn't work.

Could anyone give me a direction on what to do with this?
Many thanks.

 

[Wishmaster]

Most likely an engine mount. They notoriously fail early on the 5 and cause rough running and idle. Do some searching on engine mounts on this forum.

 

[mediumchung]

Most likely an engine mount. They notoriously fail early on the 5 and cause rough running and idle. Do some searching on engine mounts on this forum.

Thanks for reply. I checked the mounts and they are still good.
I am wondering if there is ignition problem as the engine just keep shaking with rhythm when RPM < 1000 and shake gone during acceleration. Don't know why there is no code coming out.

 

[thaxman]

Thanks for reply. I checked the mounts and they are still good.
I am wondering if there is ignition problem as the engine just keep shaking with rhythm when RPM < 1000 and shake gone during acceleration. Don't know why there is no code coming out.

You checked all 3 mounts? In the 2.3L, the tranny mount is under the battery and is a pretty bad design - like a layer cake - so I am not surprised mine came apart in 3 pieces.

 

[mediumchung]

You checked all 3 mounts? In the 2.3L, the tranny mount is under the battery and is a pretty bad design - like a layer cake - so I am not surprised mine came apart in 3 pieces.

Yes I checked all 3 mounts and they looked good.

Last night I drove uphill, it was around 30 mins driving with Gear 2. After I parked my car I found the temperature was close to red line and I could hear boiling sound from the coolant reservoir. I opened the hood and found the reservoir was full with coolant and a little bit coolant leaked out from the reservoir cap. The coolant level was just at max. before I started the engine. The temperature dropped back to middle after 10 min. waiting. I opened the reservoir cap and I could smell gasoline in the coolant. The coolant color was still green and the oil didn't turn milky.

When I drove back home everything was normal, temperature didn't raise driving downhill, the shake was still there.
The coolant level in the reservoir dropped to min. level when I checked again today morning.

Look like I am having cracks in the head gasket (nervous), but still wonder if this caused engine shaking and weird coolant level.

 

[kw_da]

Yes I checked all 3 mounts and they looked good.

Last night I drove uphill, it was around 30 mins driving with Gear 2. After I parked my car I found the temperature was close to red line and I could hear boiling sound from the coolant reservoir. I opened the hood and found the reservoir was full with coolant and a little bit coolant leaked out from the reservoir cap. The coolant level was just at max. before I started the engine. The temperature dropped back to middle after 10 min. waiting. I opened the reservoir cap and I could smell gasoline in the coolant. The coolant color was still green and the oil didn't turn milky.

When I drove back home everything was normal, temperature didn't raise driving downhill, the shake was still there.
The coolant level in the reservoir dropped to min. level when I checked again today morning.

Look like I am having cracks in the head gasket (nervous), but still wonder if this caused engine shaking and weird coolant level.

Has the thermostat ever been replaced? I wonder if it is sticking - which could cause the temp problems.

 

[mediumchung]

Did a compression test and found there were no compression in cylinder 2 & 3.
Mechanic quoted $3000 for replacing a 2nd hand engine....He said changing the head gasket may not fix the issue....

 

[mazdadude]

That is not good news... How many miles are on it?

 

[mediumchung]

That is not good news... How many miles are on it?

It is just 90K miles...
I am thinking if I should try some head gasket sealer before spending money on replacing engine.
I searched on the web and seem Bar's Leak can do the job. Any thoughts?

 

[mediumchung]

Just want to give an update. I have added half bottle of Bar's Leaks HG-1 to the cooling system today, followed the instruction to idle for 15 mins, cooled down for half hour, and then drove gently for 15 miles. Shake gone just like magic! I can feel the engine power even after 15 miles driving! Let's see how long it will last

 

[mazdadude]

Just want to give an update. I have added half bottle of Bar's Leaks HG-1 to the cooling system today, followed the instruction to idle for 15 mins, cooled down for half hour, and then drove gently for 15 miles. Shake gone just like magic! I can feel the engine power even after 15 miles driving! Let's see how long it will last

Good to hear...thanks for the update. (drive2)

Working at the auto parts stores, I saw good things with the Bar's Leaks, and Alumnaseal, but you had to follow the instructions.

I hope it gives you some time to save for that head gasket repair, or replacement engine. As long as the motor was not cooked too bad, you probably do not need a whole motor, a head gasket job should do it.