HELP! :( IACV? TPS? ECM? Dies cold, High idle warm.
 

First off, being my first post, I'd like to say thank you to everyone on here for all the help the forum has already provided me with. That being said, I am currently frustrated to the point where I want to drive my 91 ls400 off a cliff. :(

Symptoms are as follow:
When I start it cold, I have to give it throttle to keep it running for a min, then very slowly let off in order for it to not die, and keep its own idle.
When I start it warm however, it starts out fine, but then the idle rmp's keep going up and up and up.

I just got done taking apart the IAC Valve and cleaning it and the hole it goes in (it was filthy)

I have had problems where it wouldn't start recently, and would just turn over, then randomly it would start again.

Well the other day I couldn't get it to start at all after parking it while running like ****** so I swapped out the ecu. with one that APPEARED to be good. It started right up and I went home.

I haven't messed with the tps.

Hopefully someone on here can look at those symptoms and just tell me what it is.
I've read and read and can't seem to find anything.

Any help is appreciated!
Thanks.

Is the check engine light on? Have you checked for any codes? How many miles? Maintenance history? The problems your talking about help but we need more info.

So then since you swapped the ecu then now all is good? I say that because you said it ran and you went home.

My apologies, I suppose that story was a little out of order.
I swapped ecus, then drove it home, after that is all the symptoms I describe etc.
But even before I swapped the ecu, the idle was high when warm, and when driving and coming to a stop it would downshift sort of hard.


There are no CEL, and the CEL DOES function, so I have not checked for codes.... I only have a an OBD2 tool and I haven't gotten an adapter yet.

There are 179,xxx Miles on the car.

It has been running FLAWLESSLY, except occasionally not starting (and that one time hard downshifting as described above) before the ecu swap. But then it wouldn't start at all, that is why I changed ecu's.

I'm getting a "new" to me ecu in the mail today, I'll post back with results...

after cleaning the IAC valve, did the idle issue go away? you were on the right track cleaning it.

so is the starting issue your main issue now? if so that could simply be a cap/rotor and sparkplug issue, in other words the car needs a tune up. when was it last done?

I just got done putting the new ecu in. Car started up fine cold and idled great, it didn't want to die at all. However after getting warmed up, the idle started searching, then it seemed low, I put the car in gear and it promptly died, then wouldn't start again. No the idle issue didn't get better after cleaning the iac, could I have a bad iac valve? Cause my next plan is to order, wait-_- and replace that. Let me know what you guys think, and thanks for the guidance so far!

OMFG. Just put in new used IACV, NOW it does the same thing this one does:

SO FRUSTRATED!

Please help me ):

What does the o ring look like on the IACV?

Pretty flattened, but, it seemed like it should still seal well.
Man I had a low idle, then I replace that thing and now it is bouncy JUST like in that video...

The worse part is even in I figure this out, I have a feeling I'm just going to be back where I was (low idle when warm and dies in gear)

Do you think it could simply be the o-ring?

Could be a sealing issue. I would get the idle stable first and then worry about its speed.

Absolutely, but I don't know what step to take to get the idle stable first.

I'm getting ANOTHER used IACV... so idk

There is a thread on the sc forum that goes into the cleaning of the IACV. He even finds a replacement oring at home depot. Take alook over there. I dont know how to post the link.

Well, this one is super clean.
And I do know which o-ring you are talking about.
I'll grab a viton replacement from miners soon.

OH YEAH, and I have some more details if it will help anyone help me.

While the idle is bouncy if I put it in gear -

(warmed up or not)
(before the iacv was changed it would just die do to low idle.)

- It will stop bouncing, but the idle is much too high, if I put it back in park, the bouncy idle continues.