500 rpm idle, bogs with any throttle
08-10-08, 11:48 AM
#1
500 rpm idle, bogs with any throttle
As noted a few weeks ago we got the car working and then took it for a short ride, it drove great for a mile or two and then started bogging and surging idle. We assumed we had a new air leak. We've spent the last two weeks or so fighting this.
The idle bumbles along at ~500 rpm and if you give it gas it will rev but bogs badly. You can move it but you can't drive it.
The timing was perfect and locked down.
We checked and rechecked the air pipes from the AFM to the turbo.
A compression test with the schrader valve taken out of the bottom (spark plug end) of the piston engine compression tester gives beautifully consistent 100psi bounces on both rotors.
We thought it was air leaking around the fuel injectors because the primary was cockeyed. We got new primary and secondary rails from Japan2La (clean parts with quick shipping), fuel injector rebuild kits with new o-rings, top & bottom grommets, filters and pintle caps from KGParts (they'd cleaned the injectors during the build) just to make sure everything was new, soft and sealing, and new air bleed o-rings from Mazdatrix. None of this had any effect.
So today we put our PVC "intercooler" on and repressurized the system with the boost pressure vacuum tube going into a vacuum/pressure gauge. Air was clearly leaking and the gauge sat at 3psi. We used some fuel hose as a stethoscope and it was clear air was leaking near the TMIC to throttle body area.
So we put our pressure cap onto the elbow to the TB and then squirted bubble juice. It was clear that air was moving around there, coming out of a hole in the fast idle controller (FIC) gasket.
When we pulled the UIM and then the FIC, it is clear the "hole" in the gasket is on purpose. But the shaft for the first butterfly in the TB was clearly the source of the air. Here is a picture of the stock gasket.
So we made a new gasket without the slot to address the air leak around the shaft. Redoing our pressure test it was running 6 or 7 psi off the boost pressure line and it wasn't leaking air there anymore. And we hadn't touched the pressure regulator on the compressor so it's apples to apples.
Now the engine runs just as badly, but super rich with lots of smoke. Same troubled 500 rpm idle.
I'm at a loss. First, why would Mazda have put in an unmetered air leak and second, WTF is going on?
It's 100 outside and I'm frustrated as all hell.
Thanks,
Jim
The idle bumbles along at ~500 rpm and if you give it gas it will rev but bogs badly. You can move it but you can't drive it.
The timing was perfect and locked down.
We checked and rechecked the air pipes from the AFM to the turbo.
A compression test with the schrader valve taken out of the bottom (spark plug end) of the piston engine compression tester gives beautifully consistent 100psi bounces on both rotors.
We thought it was air leaking around the fuel injectors because the primary was cockeyed. We got new primary and secondary rails from Japan2La (clean parts with quick shipping), fuel injector rebuild kits with new o-rings, top & bottom grommets, filters and pintle caps from KGParts (they'd cleaned the injectors during the build) just to make sure everything was new, soft and sealing, and new air bleed o-rings from Mazdatrix. None of this had any effect.
So today we put our PVC "intercooler" on and repressurized the system with the boost pressure vacuum tube going into a vacuum/pressure gauge. Air was clearly leaking and the gauge sat at 3psi. We used some fuel hose as a stethoscope and it was clear air was leaking near the TMIC to throttle body area.
So we put our pressure cap onto the elbow to the TB and then squirted bubble juice. It was clear that air was moving around there, coming out of a hole in the fast idle controller (FIC) gasket.
When we pulled the UIM and then the FIC, it is clear the "hole" in the gasket is on purpose. But the shaft for the first butterfly in the TB was clearly the source of the air. Here is a picture of the stock gasket.
So we made a new gasket without the slot to address the air leak around the shaft. Redoing our pressure test it was running 6 or 7 psi off the boost pressure line and it wasn't leaking air there anymore. And we hadn't touched the pressure regulator on the compressor so it's apples to apples.
Now the engine runs just as badly, but super rich with lots of smoke. Same troubled 500 rpm idle.
I'm at a loss. First, why would Mazda have put in an unmetered air leak and second, WTF is going on?
It's 100 outside and I'm frustrated as all hell.
Thanks,
Jim
03-25-12, 09:21 PM
#2
Ive been fighting a vac/pressure leak for weeks and I thought it was a leak at the greddy elbow to the TB. I smoke tested it today and found the leak you mentioned above. My car 1988 Tii has low idle and low vac/boost readings. What did you end up finding wrong?
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