92 Ls Running Rough & High Idle

[WeSki]

1992 LS400, 328K miles

The following was replaces at 300K miles:

Timing Belt, Idler pulleys, Water Pump, Crank Seal, Cam Seals, rotors,

Caps, Wire set, Spark Plugs

At about 327,700 miles the Left side ignition coil failed; replaced

both the left and right coils and that seemed to fix it. After driving the car
for a short time I noticed a slight shutter at idle, kind of like a miss fire. I
was getting 19 PMG but the shutter, kind of like a miss fire, got worse then
the check Engine light came on. I also notice a reduction I power.

Code 24: Intake air temp. sensor signal

Code 71: EGR system malfunction

The 12VDC plastic connectors to the Coils fell apart and replaced them

with Lexus connectors; the wire and pins were ok.

I have checked the following:

All ignition wires; all within specified ohmic values

Checked all spark plugs

Left and Right Cam Positions Sensors: Both within specified ohmic

values

Cleared the code drove the car for about 15 miles (still a shutter at

idle) when the Check Engine Light came on. Same codes. The car still runs
pretty good at cruseing speed but I’m getting about 19 MPG HWY instead of 25
MPG Hwy.

A website discussed that a dirty throttle body could cause a Code 71. I

pulled the throttle body and it was filthy dirty. I cleaned it up and blew out
the passages. The engine started right up but it now runs rougher and idles
higher, 1150 RPMs, it used to idle at 650. I have driven the car for about 20
miles in this condition, no check engine light yet. I’m stumped. I welcome your
feedback, hits, tips and tricks.

[Exhaustgases]

Where did you get the "Lexus connectors" ? Part number please.

If it hasn't been replaced, the ECT Engine Coolant Temperature sensor, is something that can cause problems. Also when LS400 strangeness begins, the ECU capacitors are also suspect. Idle air control valve can cause some problems, and also check for manifold leaks. When did it start being bad? Right after the work? Also these engines have mechanical type followers meaning that the intake and exhaust clearances need to be checked. O2 sensors are suspect too.

And per your codes the egr could be your manifold leak source, remove and clean it and make sure it works.

I'd say first find and fix whats causing the codes, then go to the other items.

[WeSki]

Thank You for your reply.

I purchased the connector from Lexus, part 90980-11246. It is a common connector body for repairing connector to ignition coils for many Lexus and Toyotas. I only replaced the body of the connector the wires and pins were in good condition.

No, the ECT has not been replaced, I will look into that.

I've seen post on the ECU Caps, I'll look into that also.

I haven't looked at the Idle Air Control Valve, I'll check that too.

Yes!, I DID find a vaccum leak. One of the 3 vaccum lines on top of the Throttle Body was not seated. I must not have connected it when I clean the Throttle Body. After connection the line the engine smooth out but not completely. The Idle drop also but not all the way. The engine is now pretty much running the way is was before I cleaned the Throttle Body. I didn't see any other manafold leaks.

I cleared the Codes and drove the car today and got a check engine light, Code 71. Cool we're making progress no more Code 24.

EGR. A few weeks ago I did pulled the EGR and it was dirty and nearly pluged. After cleaning it I sucked on the vaccum line tube and it was real tight. At the same time I had someone watch the little rod inside the EGR move as I sucked on the line. I blew on the emissions tube and it seemed tight also but didn't actuate the vaccume diafram at the same time. Could I still have a bad EGR?

The sysmptoms now are that the engine is still has a bit of a miss to it. It also is stays at a fast idle for long periods of time. I can run the engine up to operating temp and it will stay at a fast idle. Then after several miles of driving I will notice that the idle has dropped back down to the 650 RPM range and then the idle seems to be ok from there but the (what I am calling a miss fire) is more noticable.

I don't understand what is meant by "mechanical type followers meaning that the intake and exhaust clearances need to be checked", can you elaborate?

I will look into the O2 Sensors; they were replaced at around 245k miles.

I really appreciate your input.

thanks

[Exhaustgases]

And just so you know I am not advocating just jumping in and replacing parts, the ideas are just to go there and look and check type of deal.

The valve clearances need to be occasionally checked. I am not sure of the factory recommendation for it. In the old days it was a more frequent deal on mechanical type engines vs hydraulic lifters. On these LS400 engines they will go pretty high miles before needing attention. I would say 150,000 miles or maybe at the scheduled timing belt replacement. You remove the valve covers and use a feeler gage to check between the cam lobe and the follower ie the part that contacts the cam. Adjustment is accomplished by purchasing the correct size puck or metal disk that fits in a counter bore. You then remove the existing one and replace with the correct size one.

This may help explain it. https://www.youtube.com/watch?v=pKEkOdQuJR4

[WeSki]

Thanks for replying again,

No, I won't run out and get new parts, just looking and troubleshooting.

Thanks for the valve clearance info, I'm with you now, I just didn't make the connection from you last post.

I pulled the IAC and cleaned it up, it wasn't to dirty however I found the following

The resistance between pins is 22 ohms, the specs I found on this site call for 35 to 50 ohms or there about.

I applied DC to the pins per the same post an nothing more than a bump in the plunger when applying DC.

I also noticed a hair line crack in the black casing.

I'm not sure where to go from here, new IAC? a used one on eBay? I searched for rebuild parts but no luck.

I'm reluctant to spend too much on the car as it won't pass smog and CA will give me $1000 for it being a gross polluter. I feel like I'm almost there in getting the trouble figured out; I hate see it go but I don't know.

Thanks again to all.

[RA40]

A car with this many miles those are good parts to replace and be confident about. When symptoms persist inspite of known fixes, have you done the ripple test to verify the ECU operation? Have you had it smogged since then...what results?

[fsuguy]

my $.02:

Have you verified that your Throttle Position Sensor is not on its way out? This should be a pretty quick fix; also, you may be able to pick up a used IACV from a boneyard for relatively little, or alternatively rebuild your own one if you are careful (aluminium housing and surfaces can be easily damaged!) - it will require a careful disassembly and then some cleaning - biggest problem I found during disassembly was the three tiny flat-head screws almost getting stripped due to rust. There are two bearings,either or both of which may be failing, but an off-vehicle test will let you quickly determine whether the IACV is working properly or not; I have read where a simple oiling of this part resolved issues, but your situ may be different, if it is the IACV. There is a good breakdown for this part (IACV) on the Aussie site, IIRC.

good luck

[Kdavis83]

Did this ever get resolved???

I just bought a 94 ls400 w/181k On the clock, and I am having the EXACT SAME problem.

Replaced both coils so far, hunting down air leaks now. Let me know!

[Exhaustgases]

I discovered that the Idle air control motor bearings go bad and start to seize up and that causes all sorts of problems with idle and such.

[Kdavis83]

Ah, nice...thanks for the tip

I saw somewhere online a company who makes a drive by wire replacement for the IAC stepper motor....intended for aftermarket Ecu's, but maybe would work with factory?

Food for thought. Thanks again.

[WeSki]

I never did resolve the issue but I do think I found the last straw problem. The EGR tube the connects to the back of the intake manifold and drops down to the right exhaust had a crack in the accordion portion of the tube. At that point I punted, the cost of the tube and the labor time for me to change it out was just not worth it to me. I scrapped out anything that was of value on eBay, about $1000. Then hauled the scrapped out car to the scrap metal yard, $100. It was sad but it was the most I could get for a car that wouldn't pass CA smog and was going to cost a bunch of time and money to get it smog worthy. Best of luck to you all. I'm now at 211K miles on my 2000 LS400.

[Spartan0536]

Just thought I would ask, but can you confirm if your ECU has been repaired recently, I had some seriously bad idling issues that would lead to the car becoming inoperable, and once LSCowboy replaced the capacitors in my ECU, gone, back to silky smooth.

[WeSki]

Thanks for the tip but no I never got that far. One of the main issues was that the EGR tube that runs from the intake manifold to the right exhaust was cracked; the tube was pricy and a pain to change. There were multiple other issues with the car that were going to cost over $1000 in parts. The car had over 330K miles and wasn't worth $1k running. I found a 1994 LS400 with only 130k miles for $2500, bought that, scrapped out the 92, kept what I could use for the 94 and sold the rest on eBay. Made about $800. I drove the 94 for just over 180k, sold it and bought a 2000 LS400. Great cars.