GenericUse

Alright folks, I'm back again. My ailing 1993 LS400 keeps getting worse. I thought it had exhaust leaks, but it was just oil smoking on the exhaust manifolds after the car sat for too long. The EGR valve leaked badly, so I blocked it off with a piece of exhaust gasket - it is no longer possible to buy new EGR valves for the first-gen Cali models, along with most of the other Cali-specific parts. This, unfortunately, solved nothing. I sent my ECU in to be fixed - almost no change in how the car ran. I replaced the injectors with new ones - nothing.

I'm getting really tired of driving the tortured thing every day.

Occasionally, it'll have plenty of power - not nearly as much as it did when I purchased it, but enough to be passable. Then, it'll lose enough after a stoplight (or just randomly) that it takes me 20 seconds or more to get up to 40mph - I can't press the pedal down much more than half, because if I do, the engine will surge and then immediately try to stall in rapid succession, over and over again, until I let off the gas. After it stops doing this, it manages to lose even more power. Then, randomly during the drive, it'll go back to having a passable amount of power. Sometimes it'll surge lightly while cruising. The engine will also make a groaning noise while it's low on power. It's not the ignition coils, the spark plugs, or the wires - wires and plugs are new, and I tested both of the coils by temporarily replacing them with a new coil. This also changed nothing. The fuel pump is new as well, and the filter only has about 2k miles on it. Fuel pressure is within spec (44psi IIRC). Air filter is new. Battery is new. Alternator is fine, the P/S system leaks but not near the alternator, and I've tested it as well. I've ordered an OBD1-OBD2 adapter so I can take it for a drive and see if anything looks wrong, but last time I did this (only idling because the only OBD1 reader I had access to had a failed battery) nothing looked out of the ordinary. I am, as always, completely out of ideas.

400fanboy

Have you done a vacuum test? Both on cylinder compression, but also testing the rubber hoses which if they're original, are getting on 28 years old and should be replaced anyway. It's possible you may have a vacuum leak. I would start here next if car was sitting for an extended period, as that always causes problems when you aren't regularly heat cycling all the components.

Hopefully the OBD2 tells you more information. Because until then you're just walking down the checklist of "engine surging" problems.

Yamae

+1 for the vacuum leak. It would be the best to use a smoke machine to troubleshoot the leak.
It was not my car but I have experienced an intermittent vacuum leak problem at my local shop. Most of vacuum related hoses were already replaced by mechanics but the surging problem was not fixed. I suggested them to use my home made smoke machine and they found the leak at the gasket used between the intake manifold and the engine block. Replacing the gasket fixed the problem completely. Mechanics there were surprised to see how the smoke machine was effective and they ask me to use mine time to time after that. It is not widely used here in Japan, I need to add.

GenericUse

I have actually replaced all the hoses - twice, for some of them. Don't buy Prestone vacuum hose, it goes plastic-y withing a month. I have to use fuel line for the smaller hoses because nobody sells the correct size vacuum hose near me. I will use a smoke machine next time I get the chance, though - that's a good idea. I've already got the intake gaskets as I thought I would need them when replacing the injectors, there's a chance removing the fuel rail bolts and tightening them again made the leak worse - but the car didn't start surging until about two weeks ago, and I changed the injectors in August.

BNastee

Sorry if I missed it in a previous post, but has the timing belt skipped a tooth? Wouldn't explain the intermittent bad running, but who knows.

400fanboy

You can also go to a car meet, head to the Subaru section and ask a couple guys with vapes to blow around your engine block. That'll do the trick as well 😁

CLLEXUSS

I might start evaluating your intake areas and throttle body areas if you haven't already, might be something amiss in or around the function of the throttle body.

oldskewel

iTrader: (1)

On the vacuum hoses, I've had great experiences with silicone hoses such as this:
https://www.rmeuropean.com/Products/...FG21-V592.aspx

They look like they'll outlive any car they're installed on.

Thanks for the warning on the Prestone hoses. That's another thing I've noticed - that FAKE rubber is easy to sell and tough to detect until a few months to a year down the road.

deanshark

Just as a test try unplugging your AFM (Air Flow Meter). The Intake Air Temp sensor inside goes bad and it will not throw a code. That might be why it's intermittent. My 93 was doing the same thing til I unplugged the AFM then it ran beautiful. I don't know for a fact if that was the problem cuz I never got it replaced before retiring the vehicle. While unplugged it was just dumping raw fuel in so the mileage was bad and it killed the O2 sensors. So if it does start to run good don't leave it like that too long before repairing it.

GenericUse

Nope. That was something I checked while I had everything apart for the injectors. Thought it had for a bit, because the marks are in strange places.

GenericUse

I do have another throttle body - I scratched the backside of the current one up a bit when I was putting it back on the car, but only near the stud holes and none of the scratches are very deep - barely even catch a fingernail. If I have to take the intake off, I'll probably replace it as the other one is in better shape. I've already replaced the plastic intake part that's in front of it, as it was starting to crack and the rubber seals on the ends were wrecked.

GenericUse

So, for ****s & giggles, I unplugged the MAF today for part of my drive home. Absolutely no issues, I floored it and IT WENT. I then stopped and plugged it back in, as I'd rather not replace the cats and O2 sensors as well, and all the issues returned immediately. Think it's safe to say deanshark was right on with his guess.

deanshark

I'm not saying that is definitely your problem. And I'll say this again, "I don't know if the AFM was the problem on my 93". Towards the end of life for my 93 I also had a bad ECU so it could have been that.
Having the AFM unplugged puts the ECU into "limp mode". I would test the AFM before just replacing it. When I had mine unplugged it also threw a code for O2 sensors.
When you unplugged it, did it then throw a code for the AFM? If not then your ECU might not be perfectly correct even though you had it "fixed".

Yamae

+1
I worry about the ECU board is damaged by the leaked QAS liquid. It is very strong alkali and it is the often case that copper traces are eaten and sometimes the internal layer is eaten too when old QAS capacitors are leaked badly. Surface copper traces can be mostly fixed connecting remaining nearest traces but the internal one can't be seen and can't be fixed simply. The capacitors replacement needs to be done before the problem becomes serious.

GenericUse

If it helps any, only one cap was visibly leaking, and not very much. The others were swelling. I would've taken a picture but it's difficult to hold that board open and hold a phone at the same time.