flipmode64

Can't figure out this low idle problem.

Once the car is warmed up and its sitting in PARK the tach shows it idling at 200rpm.

It just started all of a sudden one day.

If you stomp it, it will shift early at 5000rpm, but it still seems to go to 80kph in 1st gear which it did before @ 6000rpm....

I have:

1) swapped ECU's - no difference
2) swapped AFM - no difference
3) Tried adjusting TPS, it will raise the RPM but only to 400rpm, then when I put it into D it made a HUGE clunk and jerked the car, moved back to original position with low idle and theres still a minor jerk going to any gear, but its always been like that since I got it.
4) ran a propane torch gas around all vacuum tubing, cant find a leak
5) removed IACV, cleaned it, and also swapped the larger bearing out as it seemed a little stiff but wasn't grinding - no difference

ive replaced all spark plugs and wires.

it idles FINE, no hunting, no rough idle.

if I hold the RPMS at 650 where it should be, it seems louder than 650 SHOULD be. Also when hold it at 650, and ONLY at 650 and let the gas off, it will super bog down to under 200 and then figures itself out and climbs back up to 200ish and sits there.

on the highway im doing 100 kph at like 1300 rpm, way too low. certain times when i let go of the gas on highway speed its also like it goes out of gear, you can tell there is a power loss at highway speed but if you gun it it will switch gears and climbs speed fine.

if i put the tranny into L it will run all the way up to 5000 and then fuel cut it seems like until i shift to the next gear.

I am changing my coolant sensor tonight, that is the last thing i can think of.

sorry for the huge post but trying to give all details.

is there something i'm missing?

flipmode64

Changed Coolant Sensor and no change.

dicer

So then the tachometer must not be reading correctly. LS460's must have that problem.
If it was truly idling at 200 rpms, it would be jerking and missing, sputtering and all that.

flipmode64

Sorry forgot the mention this is a 1991 LS400. I'll post a video of whats going on later today.

timmy0tool

iTrader: (7)

when was the last time you changed your transmission fluid? the trans puts a load on the motor esp in gear. there might just be more load than normal.

what ECU did you swap it with? one that was fitted with updated capacitors? i suspect that the tach is off due to the ECU. consider changing the capacitors, it's a known problem for 1st gens which is an inevitable repair.

flipmode64

Transmission fluid has been drained and filled multiple times over the last 2 years, before the problem started.

I can't see it being the ECU as I swapped out one with the exact same part number and nothing at all changed and has the EXACT same symptoms.

Because this problem happened overnight im going to be swapping coils and if that fails, get new distributors and rotors as the next step.

If any has any other ideas let me know. thanks

flipmode64

Also it seems to be getting a little worse, when i accelerate swiftly, i am getting misfires around 2500-3500.

dicer

If you have spare parts then yeah do the swap deal. If your paying for them I'd look more for the real cause of the problems. Did you recently put gas in it before it all started? Is it running either lean or rich? What kind and when have the spark plugs been changed?

flipmode64

So I swapped a good known coilpack to both of them on the car. No change.

Cleaned throttle body a 2nd time, no change.

This has been going on for a couple gas tank fills at least. No it was fine driving to work (50km) and then on the way home i noticed it was idling low.

I seem to be getting INCREDIBLE gas mileage due to the low idling problem as im doing around 1300 at 100kph on the highway.

I recently put in denso iridium plugs and denso wires. The issue was happening before this on the old plugs and wires.

What would you guys recommend next? Distributors and rotors? Running out of options here.

flipmode64

What I dont understand is why it will still climb to 80kph in 1st gear, yet shift at like 4700 rpm. from what i can remember of the sound it make when you go wide open, it does sound like its reaching the 6000rpm sound if that make sense. Also today for the first time since i noticed the issue, when i put it into reverse the rpms went really low and then stalled, started back up fine, did it again at my house when i went to back out of the laneway. WHAT IS GOING ON

dicer

Since your in CA why the KPH? Without looking for a calculator and changing that to MPH most of us don't know what it is. Its not making sense first it is idling really low, and now going into reverse it goes lower?

And besides go back up to where I said the tach is reading the wrong thing. That is your problem. Just look at what you said about it reading too low at 100KPH !!!!!!!!!!!!!!!!!!!

I wish Yamae was on this one. Changing the distributors will do nothing to fix the problem. You need to either fix the tachometer or the signal source to it.

cobalt91

If your having misfires, I would finish inspecting the ignition system. Pull the caps and rotors and inspect them for cracks or other signs of damage. Also look for vacuum leaks. Are the any codes from a CEL? ( check engine light)

dicer

He originally says it does not miss. I said it would if it was idling as slow as he thought it was.
It is obvious that the Tachometer or if no one knows what that is its the RPM gauge, is not reading the correct RPM, he talks about it reading too low for the speed he is driving at. So its either the gauge or the associated circuitry that runs it.

flipmode64

Not sure why its set to california, im in canada.

It shows idle at 200 rpm when in D, only twice when i put nto reverse has it chugged and then died.

I dont understand how the tach would give me low power and misfires when i accelerate quickly

flipmode64

I am going to swap out the rotors and caps from a donor 94 that i have.

Would a vacuum leak cause a misfire when accelerating?

NO check engine light at all. My trac light comes on after 10 pump cycles, but its done that since ive got the car.