inkredible

I've searched this topic on here.

I have a 1992 Lexus SC300 Stock 5 speed W58 with 200k miles. The car has a rough idle only with a warm start. cold start, the car is fine, but if I start the car with a warm start it idles rough. I changed the plugs twice. I changed the tps. I am thinking the O2 sensor now. Am I looking in the right direction?

1JZPWRD

iTrader: (59)

I am sure you have checked the check engine codes, if any??? If so, what is it telling you. Maybe a vacuum leak. Could be clogged cats or bad 02 sensors.

SC400slide

iTrader: (11)

An unset TPS, vacuum hose disconnected or cracked, catalytic converters, may even be the o2 sensor(s). First check for a CEL and codes though.

inkredible

Forgot to mention in the original post. I checked for codes and I have no codes.

I considered my cats originally, but I just did emissions and passed while the car was experiencing this problem. I would think if there was anything going on with the cats, I would have failed emissions.

I've cleaned my MAF. I'm leaning toward a vacuum line or o2 sensor, just because when I press the gas slightly to raise the rpm to 1000 rpm, the engine smooths out.

inkredible

Update. Today randomly while driving in normal city traffic, the car decides it wants to idle at 2000 rpm.

I checked for codes again, and still not codes. I've checked all of the vacuum lines, throttle cable, MAF, and TPS. I also, reset the ECU and let the engine cool and do a cold start. The car did the same thing, just maintained the 2000 rpm idle even after the engine reached normal temperature.

I was able to put the car in 2nd gear and go up a hill from start with out pressing the gas once. The car is possessed.

luxryslide

im having the same exact problem on my 93 sc300 and i can not figure this out for the life of me have you had luck fixing it yet if so howd you fix it

inkredible

Fixed for now but, not sure how I did it.

On Friday night, I checked my vacuum lines and reset my ECU repeatedly. I took the car out and redlined it in 1st- 3rd gear. The idle went down to 1000rpm. That's way better than 2000rpm that I was doing. Let me remind you, I have a blitz exhaust and my neighbors were giving me looks while pulling into my driveway.

Saturday morning the car was running fine and idle went to the normal 800-900rpm. I drove the car the entire day and noticed the car was hesitating then surging between 500-2000rpm. In 1st gear I would let off the the clutch slightly and the car would stall unless I gave it a lot of gas than it would catch an pull at 1500-2000rpm. It would hesitate and surge everytime I pressed the gas while the car was under 2000rpm.

Sunday, I took the intake distributor cap, and TPS. I sprayed the distributor with compressed air, cleaned the TPS with isopropyl alcohol and spreayed it with compressed air.

I read how we shouldn't use MAF cleaner on our Karman Vortex MAF's. I ended up spraying compressed liberally on the MAF.

The car has been running fine all day, but I can tell there is still an issue. The idle is not as rough, but it is not as smooth as it was. I'm just happy the 2000rpm idle and hesitation is gone. I was burning my clutch go from a stop due to it stalling out if I released the clutch even half way.

SC400slide

iTrader: (11)

^ good to hear. If your SC keep's surging, it is MOST likely the 2 main 02 sensors. My TPS wasn't set correctly. When it wasn't set to spec, I had a little issue I wanted to correct, so I set the TPS to spec. Now once the TPS was set in spec, the o2 sensors acted up. (bucking/surging) It's a group effort...lol. Set your car parts where they are supposed to be, and everything else will show their ugly faces. GL!

PS: Sorry if I missed it, did you ever swap the IACV?

luxryslide

I have replaced my iacv and its still up hella high like 1800 rpm i checked no vacuum leaks if i move my timing to tdc it goes down to 1300 rpm but it still too high and surges took it into a shop they didnt do anything im completly lost at this point does anyone know how fix this im done throwing parts at it