Cold start issue – help needed

[garethrobinson]

I’m looking for help diagnosing an erratic idle from cold. The revs are rough for the first 30-40 seconds, then settle down normally. I’ve uploaded a video of the issue to YouTube. See here: https://youtu.be/4xifvmXCWmI

The issue started a few years ago after the throttle body was cleaned and the spark plugs were replaced. Since then:

• The throttle body, gasket and vacuum pipes have all been replaced
• The spark plugs have been replaced
• The throttle body recalibration procedure has been performed.

The idle eventually settles, however there is an occasional lack of power under full or partial throttle while driving. Additional info that might be relevant:

• The engine in question is GM’s Z18XE fitted to a SAAB 9-3
• It burns a little oil (though it’s approaching 210,000 miles).

Any ideas or suggestions would be much appreciated!

[stevieturbo]

View live data to see if there are any oddities.

Check fuel mixtures during idle etc, and also during these power loss events.

Could be as simple as an air leak, MAF issue etc.

[Richard-D]

The timings suggest that the problem is only apparent when running in open loop. I would be looking for sensible readings from MAF (and/or MAP) and temp sensors when cold. Once warmed and in closed loop, if you look at the fuel trims that will give you a clue about whether the ECU is compensating for an air leak.