Hello ClubLexus. I recently bought 2004 GS300 with 200k miles and is my first Lexus/Toyota. It has been 3 weeks since the purchase and loving the car so much. I put down about 500 miles so far and everything works like a charm. I definitely made a right purchase despite its high mileage. But this weird issue just started happening today. Today on my way to work(about 5miles from home)when it came to red light RPM dropped and almost got my car to stall. Taking off when the light turns green and there was a bog/lag that made the car struggled up till around 1000RPM and everything looked normal after picking up some speed. Once I got to the parking lot, I noticed that idle fluctuate slightly and randomly between 550-750 and also there was a slight vibration in cab that I wasn't aware of ever since the purchase of the car. I turned the AC on and off but no change. Before this idle issue started happening, I was always amazed that how smooth and quiet this inline 6 motor could be from inside the cabin. Almost felt like engine wasnt on at all from inside the cabin when its idling in P. Very quiet and smooth. What could be the problem? Did anyone here ever experience this issue before? I'm thinking it might be having a vacuum leak somewhere but it only acts weird when it sits in P at idle or when taking off from stop. Everything was fine until today and I just cannot wrap my head around it. There is no CEL neither.

 

My '98 GS300 once experienced the same symptoms. It was the Oil Control Valve (OCV) which needed cleaning and that restored the tickover to normal.

 

Thanks for the reply. I sprayed the carb cleaner on vacuum hoses to find a crack/tear on hoses but no luck. I've ordered the OCV filter on eBay just now. Filter should be here by end of this week. I will keep it updated.

 

Also clean your air flow meter with CRC cleaner to see if that helps.

 

I installed the new MAF and OCV filter together today, Have been driving around for 20miles so far and I think it fixed the issue, It drives perfect now. Seems like those parts also fixed the throttle lag as well. Thanks for your help guys!