so I have a 2008 coupe s.

i recently found a weird phenomenon that when I am at about 40-50 km/h, the rpm would suddenly drop to about 400-500rpm if I suddenly let go of gas paddle.

Do do you guys have it?

i am sensing that maybe caused by faulty fuel damper as the pressure of fuel drops too suddenly?

And also on the engine body besides the driver side intake hose, the body is coated with black dust, looks like grease mixed with dust, is that normal? Although it is not too greasy.

ps. I know it is not caused by throttlebody as I just cleaned it and I don't have rom drop in idle.
mac

 

If the question is too dumb for you to answer, please forgive me.

This is only the second automatic i own, my previous auto F150 does not do this . It would probably drop but not like from 1500 to 600 then bounce back to 1500.

And also at that speed range, if i hit and quick release gas pedal, rpm will suddenly go up to say 1500 and then half sec after drops to 600 again.

The ddrop looks exactly like this one:

 

no one knows?

 

Yep, does seem to be a rare issue you've got. Wish I could help but luckily never had such a thing. Do you have a pic of that black dust buildup, might be the source of the trouble.

 

My '08S had idle issues. Went to the dealer, had them reflash the ECM per ITB07-048B, and never had a problem since.

Something to look into.

http://www.infinitig37.com/TSB/1RZ20.pdf

 

This is what came off from that marked spot

 

thank you for helping but I don't think that s it. As I don't have a rpm increase during braking. Mine is when I let go gas pedal when coasting, rmp drop to idle then bounce back to normal. some ppl say it is a Japanese car thing that torque converter releases lock so engine just drop to idle speed even though the car is still 40km/h, and that is to save fuel but I don't think we can save fuel from like 1s duration of idling. Lol it doesn't affect driving and I don't feel jerk or jot or any unusual movements but it just bugs me.

 

I have the same problem. It's almost like its in neutral while you're in gear coasting. Then when you hit the gas the rpms jump up

 

As soon as any amount of throttle is applied, the rpms shoot up to where it should be in that specific gear.

 

it it is actually not the same.

lets say I m at 40. I let go gas pedal, rpm will drop to 600 from 1300, without doing anything, not hitting gas again, the rpm itself jump to 1300 again.

I mean I don't hit gas pedal, rpm itself drops to 600 then comes back up.

 

i found another thread about this. But look that reflash helped for couple weeks, the it came back

 

Okay that's not the same at all lol. Does it do it consistently while coasting? Mine just stays flat til I hit the gas or change gears. Does your car seem to slow down or speed up when the rpma drop or shootup?

 

i found another thread about this. But look that reflash helped for couple weeks, the it came back

 

I just watched the vid you linked. Maybe your car has trouble identifying what gear it should be in at that speed?

 

Yea alway around 30-40. And also after it comes back to normal rpm, if you just tap the gas pedal for like half sec, it will do it again.

nope car is smooth as it can be, but you do hear the exhaust tones down like when you should off the engine