kingdad

I've searched the best I can, but can't seem to find troubleshooting help, so I thought I'd ask and see if anyone has any suggestions before I give up and head to the dealer (which, unfortunately, is 30 minutes away, and might require a tow). Long post, but I want to provide as much detail as possible since you're not here to physically watch the car run.

I have a 1994 Lexus LS400, 193k miles on it. In Sept of 2007 it had a tuneup with plugs, wires, etc. (it had been sporadically driven by my grandmother or, more likely, my aunt, and was running really poorly, probably on no more than 5 of 8 cylinders based on the condition of the plug wires). It's had little things here and there go wrong (air suspension replaced w/ conventional coil-overs, PS reservoir o-ring dried up leaking PS fluid on and ruining the alternator, dash light power supply cap went bad), but the engine/trans has been the one strong point: I always brag about how well the car runs, despite the mileage.

However, this past Sunday, after leaving church, after about 2.5 miles I came to stop at a red light, and as we slowed to a stop the car bucked and the check engine light came on, followed nearly immediately by the trac off light. The idle was lower than normal (400-500 rpm), it sounded "funny" (rough, maybe), and felt like it was running a bit rough. Light changed, stepped on the gas, virtually no power; took 1/2 mile to get to 40 mph. Stopped at the restaurant where the rest of the family was waiting, had lunch, started the car (probably 45-55 minutes had passed), was running fine, no lights.

Drove home, about 2 miles or so, and pulling to a stop in the neighborhood the lights came on again, again a slightly rougher (and lower) idle, and no power. Had it floored to get going (I figure, if it's going to break, let's make it really bad so maybe I can talk my wife into a new one ), then the lights went off and power returned, was fine the last 1/2 mile in the neighborhood. Wife and family, following, said it "smelled funny" during that time.

Let it idle in the driveway, fine for a while, then the lights, "rough" sound/idle (again, low idle), and won't rev (in neutral/park) past 3000-3500 rpm. There's sooty, black smoke, and some black "dripping" (occasional drops, but enough to mark the driveway) from the exhaust, and from the exhaust it sounds "buzzy." Also, if I recall correctly, a fuel-y smell. It would intermittently go in and out of the CEL/Trac Off/rough state, and it seems fine when they're not on. I did notice, oddly, that reverse seems to work fine when in this CEL/Trac Off state, but not the forward gears.

After a while of playing with it, the CEL/Trac Off stayed on, and for a while it would not idle, dying instead (but it will run if the accelerator is held some after starting), but then it got over that symptom and would idle, but low.

I tried pulling the codes using the instructions on LexLS (http://www.lexls.com/tutorials/intro/codereading.html), but it would never give me any trouble codes. If I tried pulling them while it was running and the CEL was lit, it would sometimes act like it was trying to flash a code, but the blinking wasn't per the instructions on LexLS, and sometimes there would be "super short blinks" - not really sure what it was doing. But usually it would just go back to the "no trouble codes" blinking.

I let it sit all day Monday, and after work let it run for 20+ minutes (shifted in and out of gear, and did stress the engine in gear with the brakes on, but did not drive it) and it never gave the CEL or trac off lights - it behaved normally. Also, I think perhaps a motor or trans mount may be broken - how far should the engine rotate when reved while in gear but the brakes applied? One side would lift 3-5 inches under load, then "clunk" as it dropped back down after backing off the revs.

A few things I've checked/done recently: 1) trans fluid: it was in range (low end of the "hot" marking); 2) replaced the battery on Saturday (but it drove fine after that the rest of Saturday and Sunday morning); 3) replaced the fuel gauge power supply cap's a few weeks ago; 4) tightened a loose front sway bar arm link bolt (can't think that would affect this, though).

I'm fair at mechanical stuff, but don't have a vast knowledge/experience base to pull from here. Being that it's "on/off" I would suspect something electrical, a sensor or something, but can't get any diagnostic codes, so I have no clue.

Any suggestions? I'd prefer to be able to do whatever work myself (to save the labor rates at a dealer/mechanic), but don't really know where to start for this issue. Thanks in advance!

edtbjon

It sounds similar to a problem I sometimes have on my '95. After driving for a while on a highway and coming to a stop my idle becomes very low and the engine wants to stop. What I've learnt to do is to then just put it in neutral and turn the engine off and on with the key. After that it runs normally again.
There was a thread about a month ago on this. I recon you can find it if you search for e.g. "rough idle" and "highway". (I was just lucky to find it on top of the list, as I didn't know what to search for either.) Anyhow, in that thread there's lots of data on how to fix it. (The dealership did exchange part of the computer system, but I don't know if they do that without charging you $K nowadays. There's also an alternative fix which is DIY and much much cheaper.)

//Björn

kingdad

Thanks for the suggestion; I'll try searching that. However, in this case, it wasn't after highway driving, and it also did it while just idling in the driveway. But I'll search for that thread and see if it helps. thanks!

kingdad

I ran the car again this afternoon, drove it around the block, and can't get it to repeat Sunday's behavior. Still at a loss for now.