Have a 2001 GS300 with 150k. All of a sudden at a stop light, the idle started to drop...drops to 200 and struggles to stay on. Sometimes it'll drop so low that the dash lights up for a second, but the idle then goes back to normal. Sometimes it won't hold and the car stalls out unless i give it gas. If i give it gas for a couple of seconds, its fine again. If it stalls, it starts right back up...though one time i had to keep giving it gas to keep it started. But after that it was fine again. No check engine light, so not sure what the problem is. Decided to change out the plugs and wires since they were due anyways...also new coil boots and coil pack connectors since they all broke apart. Still have the same problem...maybe fuel pump or fuel filter? I have a 12 mile commute to work and it happens maybe once or twice during the commute...usually in the afternoon. Seems to happen more when the engine is warmed up.

 

Could be quite a few things. I'd start with checking your vacuum lines for any leaks. The next possible thing could be one of the sensors on your TB like TPS, APPS or maybe the actual motor. Usually a cel will pop up if its one of those. Again, try checking the lines.

Oh and the next time you're at a stop light and it wants to die, quickly put the car in neutral and take your foot off the brake. If it goes back up, then its definitely a vacuum leak

 

Tommy152,

A few question for you.
1. When you change your spark plugs, coils and all that are you change in that area, do you clean your Throttle Body?
2. Do you check your MAF Sensor?
3. Do you check your Air Filter?
Maybe all tree are dirty

4. Also, you maybe have a leak or a broken air hose on the intake manifold area.

 

Mr Jokster,
Oh and the next time you're at a stop light and it wants to die, quickly put the car in neutral and take your foot off the brake. If it goes back up, then its definitely a vacuum leak

I agree with you 100% on this.

 

My car just just started having the same symptoms and i checked all my hoses are fine and i cleaned my throttle body. I just ordered a fuel pump and fuel filter so i'll let you guys know the out come.

 

This was the problem in my case. I recently had my fuel pump replaced but there was not an idle issue. There were other issues while driving long distances though, and especially when I got around 1/4 tank of fuel.

 

I checked the hoses when I had everything apart to change the valve cover gasket. Didn't see any obvious cracks. Also cleaned the throttle body and maf. I changed the maf out about two years ago when it threw a cel. Also had a brand new air filter. Putting it in neutral doesn't help. When I watch the idle drop i have to put it in neutral and give it gas so it doesn't stall out on me. Got pretty good at switching feet to step on the brake and giving it gas at the same time while in neutral...haha.

 

The dealer performed a fuel pressure test and that's how I knew my fuel pump was on it's way out. You might want to take it somewhere to have it checked out.

 

Regardless if its the cause or not, I suggest swapping your fuel filter. However, I wouldn't be the slightest surprised if that were the problem. Do a search on fuel filters and hear the stories of peoples experiences

 

Thanks guys. Next step was to borrow the fuel pressure gauge from autozone to test out the pressure. I'll probably do the fuel filter regardless...besides a new maf, this car hasn't needed any repairs in its 15 years. Love this car but it's getting up there in age and starting to get some rust in the wheel well where I got hit a few years ago. I guess water was getting in between the plastic trim.