S80 rough cold start

jbrown122 · Post by **jbrown122** » 04 Apr 2012, 15:50

Hi all, I need some help with my car..
It's a 99 S80 2.9 and it is starting rough in the morning. Replaced the ETM, Spark plugs, MAF, a few coils, O2 sensors...
When I start it in the morning the idle quickly fluctuates from ~800-1500 for about 30-45 seconds (I think it misfires as well)..
When it's warm it starts fine. No driving issues. No codes.
Any ideas? Thanks.

uncletom · Post by **uncletom** » 10 Apr 2012, 20:00

I found the same symptoms and it turned out to be the Brake booster was leaking down an until it puled the the pressure down the engine was getting the wrong fuel readings as the extra air was not going through the Mas air sensor. The dealer argued with me but was soon proved wrong. Remove the vacuum hose and temporarily plug to test it.
Quick test and worth a try.