atropine

Just bought a 94 LS400 with 104k miles on the clock. Previous owner tried a few things to fix a rough idle and some hesitation/sputtering when going up a hill, but no luck. So now it is my turn to try. Car idles OK initially, but within about 30 seconds it starts to get a little rough. Not rough enough to die, but noticeable. Cruises down the highway just fine, but when you start to go up a hill it starts to sputter/hesitate. Press on the accelerator further and eventually it seems to get a little better, and once you crest the hill it gets better. Cruises on level ground at 80 mph no problem. Just drove it 400 miles and filled up twice; calculated 24 mpg at both fill-ups. Check engine light came on once right after the second fill-up, but went away within about 20 minutes. Previous owner only owned it about 2 years and says it has been this way the entire time. He says that he has replaced coils/rotors/plugs/wires, ran a bottle of injector cleaner through it, and replaced the cam sensor (friend of his thought that might be the problem). He also replaced the air/fuel filters recently. No improvement with those changes. I took off the EGR valve and cleaned it last night, but it didn't look very bad and it didn't fix the problem. I didn't electrically test the EGR valve though, and I plan to do that tonight. I was also thinking of getting new spark plug wires and new spark plugs just to be safe, and a new bottle of top shelf injector cleaner. Also I was planning to clear the stored engine codes so that I have a fresh start for when the light comes on next. Anyone have any other ideas on a methodical diagnostic process?

deanshark

Before you clear the code, retrieve any codes that are in there. http://www.lexls.com/tutorials/intro/codereading.html Then you have somewhere to look at if it doesn't come back up. To me it sounds more of an air/fuel problem then ignition. Check out this link also. https://www.clublexus.com/forums/sc-...on-issues.html

tonyfazt

"He says that he has replaced coils/rotors/plugs/wires, ran a bottle of injector cleaner through it, and replaced the cam sensor (friend of his thought that might be the problem). He also replaced the air/fuel filters recently. No improvement with those changes."

OK on your trip u said that the cars check engine light turned on after fueling up
did u turn the car off.

try it again turn on the car warn it up then drive like a 3-5 mile loop go back home turn it off} then turn the car back on if the CEL light stays on sound to me like the ecu when the CEL is on does the car loose power

check for codes to be safe i just bought an ecu and solved alot of problems because my last one went crazy the CEL would always be on and it would say my afm was bad (codes 24,31 )even though i changed it about 6 times
now i got code 13 only that my timing or cam sensor

atropine

thx for the quick responses and great info. i will go through that first link asap. i cant find an egr modulator (was gonna change that filter) on my car-- does my 94 not have one?

deanshark

I think the 90-94 engines are all the same. http://www.lexls.com/tutorials/emission/egrfilter.html

lex8000

WHen I got my 93 with 120K or so, it didn't idle rough but just hesitated under load and did notice it was worse going uphill. I did a lot to fix it totally (and didn't get a check engine light) but the two things I did which you haven't done yet is to clean out the plenum, and change the transmission fluid and filter. I don't think your issue is transmission fluid related, but if the plenum hasn't been cleaned it's not too hard and made a big difference for me. Just something else to think about. Mine was FILTHY.

atropine

where is the plenum located? sorry i sound clueless...

deanshark

A plenum is an intake manifold. I've never heard that mentioned for an LS400. Usually if there is an upper and a lower intake then the upper would be the "plenum". He could be talking about cleaning the throttle body to get all the carbon buildup out of it. You could do a "Seafoam" treatment. (search for it) I don't think it would help your hesitation problem but it can't hurt.

atropine

Update: I jumpered the fuel pump ECU as described in the LEXLS tutorial; I could hear the fuel running as the tutorial describes, but this did not fix my problem. Prior to doing this I retrieved the stored engine codes; I got a 13, a 25, and a 26. Cleared the codes, dumped some fuel injector cleaner in the tank, and drove 75 miles to work. I also changed out the PCV valve just because it was cheap and easy. At one point today the check engine and TRAC lights came on for about 2 minutes, then went off (as I was doing stop and go driving in traffic near work.)

I also took a picture of my engine:



As you can see, my engine does not have the same VSV, VCV, and EGR valve modulator as the picture that is supposedly what all 90-94 LS400's look like.....
(http://www.lexls.com/tutorials/emission/egrfilter.html)

For comparison, I went and looked at another 93 LS400 last night, and that vehicle's engine was identical to mine.

I will recheck the new stored codes when I get a chance. Next step is to test the MAF and the other sensors/control valves as described in the above link (https://www.clublexus.com/forums/sc-...on-issues.html)

It drives well at 80-85mph on the freeway, but in stop and go traffic and when subjected to any extra work (like going uphill) it is definitely "misfiring" (or shuddering). Still not really sure if it is more spark or fuel related. I will also pull the spark plugs and inspect them when I get a chance to see if any of them have obvious changes. I bought another fuel filter and I will just put it on anyway, even though the existing one is supposedly only 10k miles old. Then start checking the plenum and anything else I can think of.

tonyfazt

i just got rid of code 13 today
its the timing belt do it over
try it out its not too hard
but it is a 2 person job

but i didn't have the other 2 codes
just consider yourself lucky its a noninterference engine
or else the 75 mile trip would have been ur last in the ls400

atropine

i havent had time to do anything on the car yet, but i just talkef to the previous owner and it sounds like they only replaced one of the cam position sensors. i will start by testing both of them.

chadr

you are suggesting this person change the timing belt to clear the hesitation?

tonyfazt

well it worked for my code 13

chadr

I can guarantee a new timing belt was not the fix for any code you may have found in the ecu. Perhaps the old belt skipped a tooth somehow and caused your timing to be off. Then when you installed a new belt it was timed correctly again.

You could suggest this person verify the timing is still correct - that sounds more reasonable than replacing the timing belt.

lex8000

The throttle body is what I cleaned, but also the air intake it attaches to (what I called the plenum, which apparently is incorrect).

My hesitation going up hills was completely fixed by all of these:
-clean throttle body - this really did make the biggest difference
-new transmission fluid and filter
-new fuel filter

Later I had a full tune up which included new spark plugs, wires, caps and another ignition component which I cannot recall offhand. At that point the hesitation was completely gone.