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back fire through intake when in gear

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Hi guys. We have a 1998 Boxster in the shop. It's a JDM with 53,000 KM. Tiptronic.


The symptoms are a backfire through the intake manifold when in gear, hesitation and lack of power won't go through the RPM range.


What we have done; freshen the gas with new

replaced spark plugs

replaced maf

replaced engine coolant temp sensor

unbolted catalytic converter and ran without it to test for a plugged system, without change


the symptoms occur only when in drive. when in park and neutral, we can rev the engine and the soft rpm limiter stays at 4K rpm. 

however when the car is lifted onto the hoist we put it in drive, and then we get hesitation and backfiring through the intake, when we press onto the accelerator.


i have connected to the durametric and cleared/short tested for all systems and the software returns no fault codes. we also did live stream of the maf, throttle position, ect, and rpm, throttle position angle and didn't find any irrational values.


we're about to run a fuel system pressure and volume test.


update: i finished talking with the tech and he says that with the MAF UNPLUGGED, the problem went away and it worked all the way to red line. we didn't actually replace it with a new one yet.

Edited by aureliusmaxed
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19 minutes ago, Loren said:

I agree that since this happens under load a air leak is likely. But you usually get a fault when that happens.

If you have a smoke machine it is likely a time to use it.


sorry there was some miscommunication with the techs. i am about to determine if running without the MAF plugged in. we have ordered a new MAF AND will update this thread later.

Edited by aureliusmaxed
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