[diff]

Our new to us 2008 sc with 450 miles started to act up on start up as follows. Turn key, engine rotates a second or two fires revs up, or not, then bogs and almost dies and revs up again and then stabilizes at 700 instead of the 1000 or so it did when cold on first starts. Seems to be fine after that. Cannot seem to find any similar posts for the 4.2 sc jag engine. Temps are near or at freezing mark wheras temps were 50f when we bought it. Could not find anything with search except non specific iacv issues being similar. Any info on where the iacv resides would be useful.

 

[mylife1903]

Hi diff,
i had similar problems with my 2006sc
after the first start on cold mornings if i have problems i am restarting the engine in 30seconds.
And revs 1100 after one minute 700
i thing its a temperature sensor issue but dont know wich one

2 years ago it was a nightmare for me cold start, after rebuilding the engine its seems to be ok now. But main problem for me is blue puff on mornings, i will check pcv system soon.

 

[diff]

Thanks my life. I know you have had some issues over the years and I appreciate you sharing the info. I have a lot to learn about this engine

 

[MARK_C]

Clean your MAF sensor. The rev up and almost stall is a classic sign of a dirty MAF, especially if you have an oil type air filter like a K&N. Use only a proper MAF cleaner, don't use a carb cleaner or something like that.

 

[diff]

Thanks Mark. I do have the proper cleaner tucked away in the 04 thankfully. I will check the filter and afaik it will be what came with her from the factory. No real service history except that it has been in for service at more or less proper intervals.

 

[MARK_C]

Check the throttle body for grime while your there as well.

 

[brad s1]

Check the throttle body for grime while your there as well.

The throttle body is actually at the back of the motor, easily removed but it's a bit of a pain. Regardless I had this same issue, you're probably going to want to pull the TB off the car and give it a very good cleaning. Clean the blade, clean the bore. New plugs at the same time wouldn't hurt either. My symptom in the cold would be a loopy start, revving sorted it out. It devolved into loopy idle that lead to stalling. The supercharged engine recirculates a ton of garbage back up through the intake... over time it pools and solidifies around the TB blade. Eventually the crud inhibits proper airflow at idle.

 

[diff]

Thanks for the heads up on the tb. I think cleaning it may ease the less than seamless way it drives off from a standstill. no particular bog or hesitation but a delay in throttle response somehow which is making me a bit nervous about the transmission.

 

[diff]

Checked the air filter today and cleaned the airbag. I removed the maf sensor and found that the part facing the airstream definitely had an oily buildup on it. One side was reddish/orange in colour and the other side appeared black. On first start after cleaning with outside air at 28F it ran to plus 1500 and then started to back off till back at 700. I did get a startup rattle this time for about 2 seconds. So will see how things go. Seems like its the 2 to 1 downshift which is hard. So will work on a fluid/filter change. I really hope the trans will be ok but rrphils post on the solenoids has me thinking.

 

[MARK_C]

my 4.4L does the same thing, runs up to about 1400-1500 for about 2 seconds on cold start, then drifts back down to 700 or so over about another 3 or 4 seconds. Temps here have been in the 40's or lower lately.