Fluctuating Engine Idle

Guys,

To add to the ISDC technical database I would like to post my recent experience with idle rpm fluctuation on my car.

Regards,
Ciaran


Car Spec
Model: GC8 Impreza Turbo 2000, Irish Model. One owner from new.
Year: '99
ODO: 151K
Engine Mods: None
Engine Repair History: MAF swap @ 31K. O2 Lambda Sensor swap @ 121K. Ignition Cables swap @ 137K.


Problem Description:
Engine idle erratic when running at normal operating temp. The RPM varied from 500 - 1400 approx, it had an audible cadence. The idle would deteriorate badly after extended period of driving or motorway driving, the revs would plummet when downshifting between 2nd and 1st gears approaching traffic lights, on occasion the engine cut out. The issue did not manifest itself when the engine was cold.

Solution:
MAF swap. The problem was immediately solved. The power of the car has improved dramatically and the engine smoothness is better across the full rev range.

since rebuild i am getting this randomly on start up . it settles after 10-15 seconds , but i dont like it .

have been told its probably the alcatek ecu as they can be lumpy on idle .


its on my snag list

Was yours the latest version mac.

Remind me if was upgraded?

Sent from my SM-N910F using Tapatalk

yeah , was sent over for update before install

Great layout for a thread, you made it easy for others to read what was occurring. You included the condition, cause and correction.

Quite interesting as i had exact same problem and i cleaned maf it was actually better still not right dough, might swap after build

Great write up and solution, fair play man!

Very descriptive man fair play.
Bound to come in handy for people ????

Tad said:

Quite interesting as i had exact same problem and i cleaned maf it was actually better still not right dough, might swap after build

Great write up and solution, fair play man!

Click to expand...

Here's something further that may help you decide to go for the swap, the power and engine smoothness in my car post swap is remarkable, I now believe that there was a slow gradual deterioration in the MAF sensor before it ultimately failed hard and affected idling. I believe the deterioration was barely perceptible to me therefore I became accustomed to the decrease in performance and was not alerted to the impending failure. This of course now makes me fret about how long the engine ECU was getting bad data from the MAF and the implications for combustion management. Interestingly there is a YouTube video from the guys "MRT Performance Australia", [https://youtu.be/_uF9M0WEs8w?t=3m55s], in the video he stresses the importance of the MAF and actually recommends the proactive replacement of the part on an annual basis.