For a while now I have been having an issue with loss of power & shuddering while driving and car reving at ~1200 RPM for good solid 2-3 minutes when I start it first thing in the morning. as near as I can determine problem is much worse in summertime than in winter. I have to let the car settle and drop down to normal RPM range before I put it in gear. if I put it in gear right away, it will shudder for couple of minutes or worse even stall. so far I have changed DIC, sparks, all of 4mm vac lines and throttle body.

I am strongly suspecting that this is not one problem but combination of problems that is causing this behaviour.

* changing throttle body made shuddering much more tolerable
* changing DIC made loss of power less noticeable
* changing vac lines hasn't had much of noticeable impact
* changed Turbo bypass valve yesterday and that made loss of power and shuddering completly disappear except for shuddering that still happens at first start of the day ( but it's only been a day so far ).

What else could I look at? is it likely that my fuel pump has become weak and takes longer to prime now and is due for replacement?
Also after I changed TBV, I noticed that old TBV had it's diaphram wet with oil. is that normal or am I looking at yet another problem?


--Rajiv

Yesterday I changed boost control valve on car ( Saab Boost Control Valve | Genuine Saab | Part Number 55557331 | Free Shipping ). So far it looks like issues have gone away. car feels like it has power to spare. I still have issue of car idling at higher than normal after first start of the day. but I don't know where to look for that one

High idle could be a vacuum leak. I'd pursue that route and check for leaks.

Thanks for quick response and guidence. I have changed most of 4mm lines already. at this stage I think I will just take the car to local Indy and ask them to do vac leak test. I believe they can test the system under pressure with colored smoke or something.

Are your hoses crumbling and leaving carbon on your fingers? If yes - replace with new silicone line. Much nicer and lasts much longer.

Suspect your brake booster or the check valve to the booster in the hard line.

Have someone with a scan tool pull up your multiplicative fuel trim values and see if your mass air flow is way off the charts.

Is that something that can be done with standard OBD scanner or is this the job for techII?
I will check break booster tonight.