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Discussion Starter · #1 ·
ok so my idle in my 92 si bounces and doesn’t seem to stop, i took my intake off and plugged the top hole with my finger and the engine ran normally what does this mean. (what does that top hole do and how to i fix the bouncing)

i also already replaced the IACV and i tightened down the FIAC and cleaned the FIAC, coolant also doesn’t see to be a problem and vacuum leaks are still a mystery cause i don’t really know how to look for them but i don’t think that’s the problem.
 

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What this reads to me is something is missing from your intake that helps regulate the vacuum system that regulates idle and the revs.
 

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What this reads to me is something is missing from your intake that helps regulate the vacuum system that regulates idle and the revs.
ok so a little update my car is driveable i unplugged the map and tps sensor still havnt fixed it but my guess is a vacuum leak somewhere
 

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ok so my idle in my 92 si bounces and doesn’t seem to stop, i took my intake off and plugged the top hole with my finger and the engine ran normally what does this mean. (what does that top hole do and how to i fix the bouncing)

i also already replaced the IACV and i tightened down the FIAC and cleaned the FIAC, coolant also doesn’t see to be a problem and vacuum leaks are still a mystery cause i don’t really know how to look for them but i don’t think that’s the problem.
a little backstory if it helps i was being stupid and racing on the highway with my cousins (idk why, my car is slow) i was going like 135 for like 2-3 miles and then i got off the high way and the rpms started bouncing
 

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The only thing that is attached to the intake is the venting line for the valve cover. Nothing that should create a bouncing idle. Everything that would create a bouncing idle normally is after the throttle body/MAP sensor. How high or low is your idle? Your IACV really only creates a higher idle (lets air by) when the engine is cold. As the coolant warms up the valve closes and the idle drops. However, bouncing usually means an open system somewhere. After pegging the car for 2-3 miles you may have deteriorated some of the seals/caps somewhere. Only real way to go through it is to create the issue and go through every cap and connection by removing and capping with your finger and seeing if it fixes the problem. Be it the PCV, EVAP or any number of the vacuum lines or caps on the intake manifold. With cars this old, no rubber lines or caps can be fully trusted until tested.
 

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Discussion Starter · #6 ·
The only thing that is attached to the intake is the venting line for the valve cover. Nothing that should create a bouncing idle. Everything that would create a bouncing idle normally is after the throttle body/MAP sensor. How high or low is your idle? Your IACV really only creates a higher idle (lets air by) when the engine is cold. As the coolant warms up the valve closes and the idle drops. However, bouncing usually means an open system somewhere. After pegging the car for 2-3 miles you may have deteriorated some of the seals/caps somewhere. Only real way to go through it is to create the issue and go through every cap and connection by removing and capping with your finger and seeing if it fixes the problem. Be it the PCV, EVAP or any number of the vacuum lines or caps on the intake manifold. With cars this old, no rubber lines or caps can be fully trusted until tested.
so with the map sensor and tps connected it bounces between 1 and 3k nonstop when they’re not connected it stays at 1200 rpm
 

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so with the map sensor and tps connected it bounces between 1 and 3k nonstop when they’re not connected it stays at 1200 rpm
Right, since it's making no adjustments since it reads a 0 value for both TPS and MAP so it's running (I think) entirely off a pre-programmed fuel map as it has no sensors to determine what's going on. Though I hope the car stalls out if you just pull the MAP sensor plug while the car is running, if not your MAP sensor is dead. However, once you have the sensors installed it reads a 0 TPS and a MAP that's actually too high (ECU doesn't see the vacuum you'd normally see with the throttle body closed for 0 TPS) so RPM's drop, hits the anti-stall and bounces. So it's likely you have a vacuum leak somewhere. In cars this old could be any vacuum line and possibly fuel injector seals. First check to see all the vacuum caps are in place and there's no open ports. Then it becomes a matter of removing a single line (like the fuel EVAP line on the TB) and covering the port with your thumb and seeing how the idle if affected or just buy the appropriate caps. Then IACV, the resonator line, PCV, etc, etc. Then pull the fuel rail and check the injector seals. Hopefully by then you've found it, if not one of your gaskets might be at fault.
 
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