1996 wrx sti V2 - Cold idle issues

[elliotp]

Hey Guys,

 

So I've been working my way through an idle cold start issue for a few months now without actually solving the problem.

 

So the issue is that when I start the car from cold overnight the idle occasionally drops low and subsequently idles rough. This only happens on the first run and generally only while the car has been sitting overnight, during winter it would be a little rough after sitting at work during the day but now the weather is warming up it only happens in the morning. Even if the idle is rough, i can shut the car off after it cleans up then turn it back on it runs fine.

Rough idle only lasts for about 5 seconds then the revs go up to 2k and then settles back down. So this happens more when its cold than warm and is only a couple of times a week, the other symptom I have is even when it starts fine with no idle issue, in the 5-second range if I give the throttle a blip, there seems to be a small hesitation in there. If I rev it smooth then there's no issue. So other than this initial 5 seconds in the morning it runs really well, even straight after the idle issue, once I'm on the road everything's fine. 

 

So here's what I've done to try and resolve this.

• New spark plugs
• Cleaned IACV
• Cleaned MAF sensor
• New fuel filter
• Checked vacuum lines, it looked like my brake booster line had a crack in it, couldn`t tell if it was leaking but replaced anyway.
• Cleaned throttle body

 

Previously it had an OBD code 24 which is an Idle Air Control Valve problem, the code got reset and it never came back. However looking at the codes again I do have a code 11 which is a Crank angle sensor fault so it looks like I need to replace that, but before I keep replacing parts I really want to stress test the symptoms with the community to double check replacing the sensor would be the best cause of action. 

 

Thanks