nxte

UPDATE- Switched ecus. Having slight differences now. The car turns on and slowly goes down, right when it’s about to stall jumps back up and repeats. I have literally no throttle.

Hey guys! So i have a bit of a project sc400. It’s not perfect but right as i thought things were about to be fixed it got worse. Here’s the run down of my car.

1. Maf code comes up (has a weird “cammed” idle)

2. Put the maf in, now car is throwing the MAF codes and the IACV code. I’m assuming the MAF code just hasn’t reset yet. Now yes, i’m going to either clean or replace the IACV. But I’d like some advice first. Here’s what my car does now.

Idles at 100 rpm. If you rev it it stutters like crazy.

I was just about to fix the IACV when i saw an LS400 on youtube have the same issues and he fixed it with a new ECU.

Does this seem like an ECU issue or an IACV issue? Or neither?

Thanks anyone for their help.

(edit)- all parts i’ve used on the car are OEM. i have 2 ecus because the dealership thought it needed an ecu and none of them fixed it. so i’m starting to wonder if any of the ecus are even bad. leaning towards the iacv since the code leans to that but most the time i don’t see idles this low with that issue.

t2d2

iTrader: (8)

The ECU(s) are definitely suspect, if they haven't been repaired by now.

IACV doesn't really make sense to me. It could maybe explain the low idle, but not the bad stumbling with throttle (where the IACV is bypassed). Adjusting the TPS could be worthwhile, as that's more likely to explain both issues.

Tallyhoe

Kinda had my own theory on this... I would side with ECU as well. I had a whole slew of attempted problem solving with idling, stumbling and stalling.

nxte

Yeah that’s what i’m hoping actually. The iacv screws are 30 years untouched. It was impossible to even try to get them out.

t2d2

iTrader: (8)

Make sure you use a good philips screwdriver in general, but especially on stubborn, small screws like on the IACVs. Most have tips too sharply tapered, despite being a standard size, and will slip out of the slots easily enough to strip the head. If you have bits that fit nice and snug, hitting the screws gently with an impact driver can help a bunch. When I've removed old IACVs and ignition coils at the junkyard, it's generally a two-handed affair, putting the bulk of my body weight behind the screwdriver and using both hands, to make sure it really bites into the head. There will be a sudden pop and then the screw turns easily. They probably used some sort of medium threadlock in the factory.

But, all of that is a moot point if you can solve the problem elsewhere and not have to remove the IACV.

pishta

Those IACV's have sealed skateboard like wheel bearings in them that seize up over time. Mine gave an 1800 idle. I limped it home and found the bearings almost seized, they were very difficult to move. a little oil and they were smooth again and my idle dropped to ~650. I have had 4 other people tell me they fixed theirs after checking this too. Tip on the screws: get a good screwdriver, grind the tip a little and tap the end with a hammer once your into the screw to shock the threads, it will make getting them out easier and will prevent stripping out the phillips head.