JJDAG

So driving today there seemed to be a shudder when the car would up shift but not all the time , on my way home I tried playing with it to see when it would do it. When I pulled into my driveway I reved it in park and it runs smooth at idle but when reving the engine it started to feel like a skip just about 2500 rpm through 3000 seemed to smooth a bit with higher revs. there are no check engine light the car starts right up and definitely cruises right along not realising i was constantly 15-20 mph over the speed limit. The other odd thing it did twice today the speedo and the tach were stuck at zero i tapped the top of the dash and they both started working, I dont know if that has anything to do with the rough running or not. any ideas ? I was thinking maybe one of the coils is starting to go? It has been raining for 2 days. I dont have any experience with a lexus first one ive owned and first one ive driven. Any help would be much appreciated.
Thanks
John

lexmoose

I had this issue with my 96 (shifting issue and speedo/tach going mental) when I swapped my ECU for a JDM one. So from my experience I would look at the ECU. There's a ripple test you can do apparently to see if your ECU internal capacitors are bad and need to be replace.

JJDAG

Thanks for the quick response! Not to sound dumb but what is a ripple test ? And how would I do this ? and whats a JDM ? The car has 88k on it would an ECU go bad that soon ? or is it more of a time thing?

RA40

iTrader: (6)

We've not seen much about the '99 ECU since Toyota had changed the capacitors by then. That's not to say the model year is immune but not a likely cause of problems like the 97 and earlier years had.

The ripple test will check if the ECU is within operating spec.
https://www.clublexus.com/forums/ls4...-by-yamae.html

There can be other issues to address and first thing to do is pull any error codes that may be stored. Is there a check engine light on the dash that is lit up? If so get those codes and post them for us to advise.

MngreLMatt

He said that he doesn't have a check engine light on in the original post. With only 88k , I would look into transmission and or engine mounts because these being bad can cause a super rough feeling especially at speeds. If it was missing, theoretically you'd feel it throughout the rpm range, or at least I did when one of the spark plugs wasn't gapped accordingly. Definitely don't look past the transmission and engine mounts though. It would be odd to see any other coil and or spark problem with that mileage. But what the he'll do I know. I have 220,000+ on my 99 for reference with zero coil or spark plug problems

JJDAG

Thanks for getting back to me. There is no check engine light on, it does come on when you turn the key on but not starting like it should, the car does start right up with no problem, When I first noticed this it seemed like a shudder on up shifts when taking off from a start in the 2000-3000 rpm range not bad but noticeable, then playing around last night I could feel it while driving, when I tried it stopped in park just bringing the rpm up it did it at the same rpm range but acted more like it was misfiring, It would rev up without a problem did not stall or idle rough. The only other thing I noticed 3 times yesterday the tach and speedo needles would stay at 0 until I tapped the top of the dash then they would work. I dont know if that would have anything to do with the other. If it is the mounts how would I check them ? I have no way of jacking the car up right now. ( gravel driveway) Thanks for your help
John

BWLS400

If it's not throwing any CE codes, it's somewhat difficult to diagnose right now. Most of the time these kind of issues go away or get worse. For instance, my '99 did something similar to yours and the CE showed intermittent misfire on all cylinders 1,3,5, and 7. I changed the plugs (simple and straight forward) and changed gas stations. Shortly after that, the missing issue went away and has not come back. Hopefully, yours will throw a CE so you have better direction.

JJDAG

Last night I was searching for this concern for a couple hours before I posted this today when I read Matts response to look into the mounts I did a search on this and found several post a couple with the exact same symptoms less the sticky tach and speedo and it turned out to be the mounts. The car does have low milage but it is a 16 years old and from what the service history states it spent most of the time in Florida so maybe the extra heat would add to mount failure. I will look further into the mounts as the car does seem to have plenty of power and has no problem with get up and go like I would expect with a misfire. Thanks guys for helping Im new to this club and to Lexus.
John

BWLS400

To check the motor mounts, you can pop the hood, put the car in drive while running, apply pressure to the brake, and press the accelerator simultaneously. If you have a good view of the engine from the cabin of the car(or have someone else outside looking at the motor), you will notice the motor torque( like it's trying to come out of the engine bay) while giving it gas. If The motor mounts are good, the motor will move a little, but nothing that should be concerning. You can search some Youtube vids to get a better idea of what i'm talking about.

If the tranny mount is bad you will notice a slight vibration throughout each gear and at highway speeds. This vibration was light, but enough to be extremely annoying. At highway speeds, mine felt like i had bad tires or something. That's the best way I can describe it. I hope this info helps.

JJDAG

I just tried this the motor jumped a good 2 inches, I ordered both engine mounts and the trans mount . I feel better knowing whats wrong. Thanks so much for all your input !
John

JJDAG

So I'm waiting for my trans mount to come in I received my engine mounts, I did find a post on installing the mounts with great instructions and pics, how ever some of the folks said to only use lexus parts as the aftermarket parts don't work well. Of course I ordered aftermarket parts so I will be returning them as I ordered the original parts from Lexus. My local Lexus dealer wanted $180.00 each for the engine mounts and $100.00 for the trans mount and had to be ordered. someone on here said to use Lexus of Atlanta I checked them they only want $105 each for the engine mounts and $43 for the trans even with the shipping cost I saved $181.00 !

Legender

I found similar prices at mylparts.com also. They seem to be very comparable.
I just purchased the tranny mount from Sewell last weekend as I did not want to wait and it cost over $60. No shipping but I had to drive down and pick it up.
Pretty sure I need the engine mounts also, but have never replaced those, but the tranny mount is easy if you get the car up high enough.

GeorgeNVA

I would recomment to run a scanner against it and see the long term fuel trims, and how they vary across all load/rpm ranges. It's not hard at all if you have a laptop, spare $50 and some curiousity.

The trims outside +-5% range indicate some problem. By +-25%, the problem is regarded as major and CEL comes on. CEL being off doesn't mean everything is ok. After all you can still start and drive it.

The problem may originate from a variety of sources, like dirty AFM sensor, dirty/leaky injectors, faulty spark plug, sticky VVT actuator etc etc.Careful inspection of the trims usually give a great insight and narrow the search down to a small list of tests.

JJDAG

Thanks George thats a good idea, for this concern I do clearly have a bad engine mount when i put the car in drive with the brake on and give it the gas the engine jumps up a good 2 inches, There are many post on here that have the same symptoms and replaced the mounts = all symptoms fixed. I've had this with many other cars just not the same symptoms and I've never needed to use oem mount aftermarket always worked fine, But I've never owned a Lexus before . I will at some point scan the car just to check it for now I plan on doing major service with timing belt and water pump , every fluid and filter in the car changed. along with the mounts. I will post the outcome after all service is completed.

GeorgeNVA

Scan is always a good idea, but the trick is who performs it and whether he keeps in mind what to look at or not.

From official Lexus point of view, any fuel trims are acceptable if the CEL stays off. However from my practical point of view, if any (or both) of the banks go above +10% or below -10% (long term), something is definitely wrong. Last episode I remember was an IS250 , reported issues were hesitation, jerky shifts, playing up idle when warmed. Fuel trims were +18%. CEL was OFF, no DTC stored. Cleaned MAF with carb cleaner, the car became pretty normal, trims settled to +5..6%