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Pulsating / Rough Consistent Speed & Idle


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Hi All,

I've had my Link G4+ in my car for about a year now and had no issues at all until now & i feel beat.

Car Info:

2002 STI - Link G4+ P+P - EJ207 - ID1400 Injectors - Flex Fuel - Blouch 1.5xtr turbo - 3 port boost controller - other standard bits


I noticed about a week ago when driving that going at a constant speed i got a pulsating shudder below ~2500 rpm and then at traffic lights or stops it would only settle to 1500 rpm, then slowly work it's way down to the 850 rpm hot target whilst making the whole car shake. The issue seems to get worse the warmer the car is. It doesn't break up at all and seems to behave the same under boost. No error codes are thrown.

Troubleshooting Attempts:

Cleaned IAC valve body + new gasket, cleaned MAP sensor, cleaned 02 sensor, checked all vacuum lines and made sure all electrical sensor connections are tight.


I have taken a log that has the car warmed up & behaving properly for the first 6:40 but then in spurts at constant speed the car tries to cut in/out (see Engine Speed ROC) and the cases it happened rather than lift/accel to break it i've purposely held throttle constant to check other ecu factors fluctuating readings.


Any help would be greatly appreciated as this has me stumped & i cannot see in the data an error. My thoughts going forward is speed sensor or something telling the car to cut all power/turn back on - maybe a cam sensor? 


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Really need to see the tune, but I see over-run fuel cut it cutting in a lot, this could be due to it never being tuned properly, or if you think it is a problem that has only recently surfaced it could be something like the TPS has moved so the calibration is no longer correct.  A quick test to confirm would just be to turn off over-run fuel cut to see if the surge disappears.  

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Quick Update - Re-calibrated the tps and turned off over-run fuel cut and the surging went away but the car puts the idle at 2100 rpm unless you slip the clutch then it will drop down to 1500 then to 850 target.


Logged the drive and will upload later tonight. 

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As an update:

The ECU has been flagging AN T1 with errors for 'ECU Fault Code 43: An Temp 1 above Error High value' and 'ECU Fault Code 44: An Temp 1 below Error Low value' which is the Inlet Air Temp sensor. The weird bit is that during troubleshooting the sensor i thought was my IAT (an additional sensor was tapped into the intercooler) was not & the sensor giving the reading was actually the MAF sensor having it's own IAT built in that is (presumably) dead.

I'll try and source a new MAF tomorrow and see what that does but i'll also research and see if the wiring was done wrong all that time ago & did not tap into the MAF wiring correctly.

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