lexsc92

Pulled the IACV to clean it today. Decided to do a resistance test first.... and the resistance between the specified terminals was 0 ohms! I believe the manual says they should be around 10-30 ohms depending on temp. I think I found my problem?? hopefully...

Alright so I let the car sit for a few days because that's when it seems to act up the most. It started rough and poured some white smoke as expected. I was able to rev it for twenty or so seconds to get the idle to smooth out. However 5 mins down the road it started acting up again. I was able to figure out the exact symptoms... -idle is fluctuating randomly (no more than 100-150 rpm difference) but you can feel a random misses here and there -coasting without any throttle runs smooth, however barely touch the gas and it bucks -give it a decent amount of throttle and it smooths right out , especially if you give it enough gas for the transmission to kick down a gear it takes right off... once you back off the throttle a bit it bucks again, let go completely and it runs smooth. Once you come to a complete stop at idle you can feel the miss again. This is starting to sound more like a MAF issue, or possibly TPS. But would it be that random? One other theory... I noticed the wire harness that plugs into MAF runs along the block, on that passenger side there's some oil seepage from the valve cover. I could smell oil burning off of it today. Is it possible that when the car sits for a few days the oil leak is causing interference with the harness, and the car runs good when driven often because oil isn't given the chance to accumulate?

Thought I would update this. The weather has started to cool down here a bit, and seems to have made the rough idle issue appear more often. Basically now I start the car when cold and it fires right up, then rpms chug and idles poorly, and puffs some white or greyish smoke for a bit. However I've realized all I have to do to make the rough idle go away, is simply rev it a couple times. Then the car smooths out like nothing happened. I did decide to change the Engine coolant temp sensor, and it did not fix the issue. However the car does seem to have picked up a bit of power. The car runs great! I just need to figure out this cold start idle issue. My next things to check are the EGR and IACV for carbon blockage. Any ideas/advice? thanks

Well I've pretty much confirmed it only runs rough if it sits without being driven for a long time..a week or so. Been driving it this week and hasn't acted up once. Drove it somewhere an hour each way and never missed a beat. Maybe the fix is to just drive it more lol.

Nope NGK, and the problem started before I changed those out. I just figured I'd do a full tune up to see if it would take care of things.

Now that you mention it, the idle does seem a little low. When warmed up its idling closer to 500 rpms. By losing throttle pressure, do you mean it feels like the response is a little "soft" and have to give a decent amount of throttle to get rolling? Oh, when I bought the car the previous owner had removed the stock intake box and put a small cone type filter on. I kept it on for a while, but bought a stock intake box and put it on a couple years back.

Would an 02 sensor issue be possible right at start up? I thought the MAF is used until the 02 sensors heat up? Engine coolant temp sensor..that's one thing I've heard can cause some random issues. It's cheap too, so I may try that first. Don't really have any mods besides wheels/suspension/mufflers. How do I actually check the MAF?

It fires right up, acts like it's going to idle fine for a second, but then starts idling very rough. You can really feel it once you put it in gear and there's load on the engine. Feels almost like a big lopey cam v8. I can get it up to speed but it hestitates/bucks through different rpm ranges, but randomly surges full power sometimes. Not sure if related but I did notice when I've driven somewhere and start the car again later the engine turns over a few times before it starts. Where typically it fires right up. This is only when it acts up though. When it runs good, which is most of the time, it runs like a champ.

Thanks for the response. I know the timing belt has been changed, and if it jumped timing wouldn't that stay running horribly? It's not transmission related as it does it in neutral, park ,etc. Transmission shifts great, and actually the engine runs great until it decides to act up. It's tough to really even have someone look at too, because by the time I can take it in somewhere it runs good again. I actually wish the car would throw a code and make things a little easier.

Hi I posted this on clublexus too, but trying to get some more opinions. Ihave a 92 sc400 without about 130k miles. It runs super strong 95% of the time, but I've had an intermittent misfire issue. The idle is rough enough to feel the car shake. Also I can get it up to speed okay, but the car will fluctuate between bucking/hesitating, with random surges of power. It seems to do it the most often when the car sits for a week or so. If I drive it regularly it doesn't seem to happen as much. However today it randomly decided to do it. But then I go back outside an hour later and it took it for a drive to have it run full power again. It's had a full tuneup: plugs, wires, caps/rotors, coils, etc. The injectors and fuel filter are also new. Good compression. I'm stumped, and not sure where to go from here. There is also no check engine light.