jfmjr

2002 Sc430 just turned 100K . On cold start car nearly stalls then for first few miles it is necessary to "caress" the gas pedal as the car bucks and acts as if it is not getting constant fuel flow. Problem has become progressively worse and independent mechanic can't figure it out after multiple attempts. worst after car sits overnight but any time the car sits long enough to cool completely, the problem is there to some degree.

VVTiBob

When was the last time the throttle body and MAF were were cleaned? And, did your mechanic scan for DTCs?

jfmjr

throttle body cleaned less than 1K miles ago. Not sure about MAF. no codes and fuel pressure was checked and was normal.

kjcole

Sounds like a vacuum leak from PVC valve or similar. Start checking those hoses.

jfmjr

Cleaned the MAF, it was so filthy I could not see any wires in the sensor until it was thoroughly doused several times with electronic parts cleaner. Tried cold start this morning and it seems to have resolved the issue. (Fingers crossed) but time will tell. Thanks to all!

jfmjr

So I thought the issue was resolved with cleaning the MAF. Car sat for 2 days in the garage and when it was started cold, it dropped rpm's then immediately kicked up a few hundred. When putting the car in drive after backing from the garage, the car again started to buck and sputter, and continue to do so for an extended time although it subsided significantly. the weather was raining and humid approx 80 degrees. any thoughts with the additional information?

scdroptop

iTrader: (1)

need to check for codes...

several things came to mind for me, but without codes it's so hard to tell

bad gas
gas cap
plugs/plug wires
fuel injector cleaning

scyul

Did you clean the TB yourself? Was it removed and bench cleaned with TB cleaner and a brush? (I use my wife's tooth brush)

If not, I would re-do it. Cleaning a TB is more than spraying cleaner in the opening and whipping it off with a shop rag. The gunk is behind the butterfly... To do a perfect job, the TB must be removed from the car.

jfmjr

I will pull the throttle body this week. Also, no codes are present and the garage scanned for any in memory? weather and temperature seem to have a significant impact on this condition.

sixonemale

Lots of good suggestions thus far. Cleaning the throttle body is a good idea as well as checking for vacuum leaks, etc. Sometime ago I had a problem with another car that was temperature/weather related - not always, but sometimes on rainy days the intermittent wind shield wipers would not work. A technician told me he would have to take a part the steering column and that it was a very complex job to fix this issue. Since it was summer at the time and it did not always happen, I waited to have it repaired, until one day I checked the windshield wiper relay and found that a small hole had eroded in it causing it not to work on certain damp or rainy days when moisture entered it. It was very inconsistent. I know this is not directly related to your problem, but it may be a good idea to check all relays and if they don't cost much, replace them. I would also check the fuel pump resistor, link below, that recently caused me a headache since it was also intermittent.

https://www.clublexus.com/forums/sc-...down-help.html

I’ve also attached a couple of PDF’s of the fuel system that may be of some use.