2L JTS Rough Idle

[Dr_Doom]

Hi, my 2L JTS has a rough idle and a bad exhaust smell. It misfires a bit on idle with the rpm needle fluctuating but no engine light. No engine codes are showing recently, but sometimes it would show a general misfire code and cylinder 1 misfire on MultiECU Scan, but no engine light. I pulled the plugs out and all were a bit black and sooty, but not wet. A compression test showed that cylinders 1,2,4 at 150psi, but 3 at 125psi, a bit of oil in the cylinder and compression increased to about 200psi but the plug looks the same as the rest (not more sooty or wet/oily). There is also no major/large amounts of smoke coming from the exhaust. I was thinking if maybe all 4 injectors are letting too  much fuel in but I want to see if anyone else has any other ideas of possible causes.

Is it possible that a previous owner tuned the ECU to run rich? (ECU looks stock) Or maybe an incorrect reading from a faulty sensor changing the fuel mixture? I have added fuel injector cleaner to try and see if anything changes but same result.

Any insight would be greatly appreciated.

[CloverleafQV]

G'day Dr Doom,

I've recently bought a 2004 JTS Spider that has the same symptoms at idle.
Have you managed to find out any more about what might be causing the problem ?

Cheers,
Stu

[bazzbazz]

May I suggest you first start off with the basics, check for any leaks or splits in the Air Intake Hose, give the MAF sensor a clean with the appropriate MAF cleaner. Also try moving the coil pack in cylinder 1 to cylinder 2 and visa versa, then if any more misfires occur see if they stay at cylinder 1 or move to cylinder 2 that will tell you if it's a failing coil pack.