deanshark

When I looked at the car during test drive before purchase it had this low idle and ran really rough while driving. Like, when it hit about 40 MPH and gave it some gas it felt like 6 cylinders. I figured no problem, I'll just give it a tune up and be good. Well, after changing plugs, wires, caps and rotors, ECT, T-belt, and now the ECU, it runs better but it still has the same problem. The throttle body is the cleanest one I've ever seen. When cold it will idle around 800 and feels like it has a skip. Then drop to about 500. If I'm sitting at a light the idle will be about 350-400 in gear and the car will hop. I need to throw it in Neutral cuz all my fat just bounces around.

It doesn't have take off power like it should. While driving it feels like it's running on 6 cylinders until it reaches about 1800 RPM then feels like 7 cylinders. (like a skip) If I'm cruising along on the highway, no matter the speed, with my foot just touching the gas peddle (RPM about 1200-1400) I can feel it jumping a bit. (like a skip) A non Lexus driver might not notice it. Hit the gas and it will kick down and go but nowhere near how fast it should be. After it gets hot it will run a touch better but still not good. It only has 85K miles on it but the previous owner didn't take too good care of it like I thought. Any thoughts on what could be causing this?
I did notice under the hood, while looking for vacuum leaks, when I raise the RPM the Vacuum Switch Valve will click, is that normal or could that be the cause or part of the cause of this? Any way to test it?

The other day I unhooked the Air Flow Meter just to see what happens. That just puts the ECU in limp mode and dumps raw fuel in. It runs faster but still like crap. Checking codes, the only thing that came up was the AFM. I plugged that back in.

Gerf

Do you have the original exhaust still on the car?

deanshark

As far as I know it's still original. (85K miles) It does sound a little weird sometimes like there may be a very tiny leak towards the front. And again, a normal person (non-Lexus) wouldn't even notice it. Especially cuz the heat shield for the back left muffler is resting on the muffler (cuz the screws rotted) so that makes more noise. (until I screw it back up)
Are you thinking maybe a clogged catalytic converter?

Gerf

Well, it's possible to have some kinda blockage. You could connect a vacuum gauge to a live port, floor it and see if vacuum drops like a rock to zero. Maybe you already tried that.

timmy0tool

iTrader: (7)

exhaust leak toward the front could be the EGR tube which is common to crack but that shouldn't cause drivability concerns like what you are describing.

dean, do you know if the fuel pump was ever replaced? what ignition wires did you go with when you replaced?

deanshark

I'm hoping that EGR pipe isn't cracked cuz after all these years of reading everyone's problems on how to change it, I don't think I'm up to that anymore.
I don't know about the fuel pump or much else on what the previous owner did, or I should say did not do, to the car. Seems like not much. Original owner was deceased and I bought it from his grandson who didn't know anything about it, or didn't care to tell me. Are you suggesting I check something on the fuel pump?
The plug wires are Denso. I won't get into why I didn't go with NGK but I did check the new wires with an Ohm meter and they were all well within spec. Plus, back when I thought I had that weak spark problem, I got a good spark out of them when I used a new plug.
But either way, this problem was present before I did all the tune up stuff.

VolumeToo

Sounds a bit like the way mine went. Obs you don't have the VVT engine so don't have to worry about oil control valves. In my case, hindsight suggests I had sticking valves in the engine - which this 'Marvel Mystery Oil' might have solved, had I known about it at the time.
Could be ECU of course, depending particularly on what year's model you have.

deanshark

No VVT-i, That's why I like the 93-94.
Marvel Mystery Oil; I used that in one of my cars way back in the 1980s but can't remember the results. My father used to swear by it though. If it's been around that long, I figure I'll give it a shot. Can't hurt, right? The PO did have the oil changed regularly according to Lexus and Carfax.
ECU; same symptoms with a rebuilt from 2013 and the remanufactured from Denso which is in it now.

deanshark

Well, it's been a month. I haven't done any diagnosing seeing how it's been 95* -100* every day all month, and way too humid. (wish I was young again )
I've only driven it about 150 miles and the car is running better as is it has more power and runs a bit smoother. Maybe the new ECU had to learn my driving better. Still has the low idle in gear (4-500) shown on the tach, which could very well be wrong cuz I'm having some other problems with the cluster anyway.
Here's what I noticed about the skip feeling; after looking at the pics I have from when I did the T-belt, I don't think it's an actual skip that I'm feeling. I was blowing up the pics to see if I could notice any burnt or fraid wires, or anything else out of the norm. What I found was a crack in the "dry rotted" rubber on the Harmonic balancer. Even though it feels like a skip there's no sound of a skip, so I figure my whole problem is not a skip, it's a shake, a pretty rough shake, in gear at idle is the worst.
I will be changing the harmonic balancer soon. Not sure when cuz $350 is pretty tight right now, but I will update when it is done.

Jake07

Hi I didn't want to start a new thread so this is one I thought I could add on to. I've had my '96 ls400 for almost a year now, 118k miles on it and it's never given me any real problems. It does idle a bit lower than I think it should. However about a week ago I was driving in the Utah mountains up a very steep climb and my temp guage started to rise above normal. I didn't want it to overheat or anything so I stopped and checked under the hood, and a bit of smoke was visible but I couldn't tell where it was coming from. Looked under the car and the drivers side catalytic converter was also emitting smoke (engine was off). I've still got a bunch to learn so that's why I'm here 😂 so is that normal for it to get hotter than usual while driving up steep hills, or you think it needs new catalytic converters, or is that even the problem?? It hasn't overheated since cause I haven't taken it up anything really steep since that.