Any oldschool obd1 mechanics here i need help with a diagnosis

[YarisSedan]

So story goes my friend has a 93 lexus gs300. I did a seafoam intake manifold cleaning for him. Next day he says his car is shaky at idle. I take it for a test drive and can feel what he is talking about. So i attempt another cleaning thinking that maybe a piece of carbon broke off and reattached itself to a valve. This time the car is worse now and occasionally stalling at idle. But luckly check engine light is on. It has a code 31 something to do with VAF sensor which i guess is a MAF sensor. I remove it and attempt to clean it with electrical contact cleaner but no change.

I assumed the massive amount of smoke went back up the intake and contaminated the sensor. I checked the price for a new one at lexus and wholesale cost is over 800 bucks. I ordred a used one on ebay and threw it in and car is doing exactly the same thing.

I am about to remove the throttle body and try to clean all the crap out and clean the idle air control valve. But i really dont want to go through all the work. Also i dont really think that may solve the problem. I guess its possible the used sensor is faulty. But the thing is there is absolutely no change in how the car ran before or after whichever sensor i use.

Any mechanics here work for toyota or lexus have experience with something like this. I am now responsible for the car since it had no problems running till i touched it and its sitting in my garage at home. So every day i get off work in working again in my garage till i fix this which is really stressful.

[Ryu]

My suggestion is to bring it in to Toyota and see what they have to say.

[YarisSedan]

From my experience the dealership has little diagnostic experience. Thier approach to repair is to replace all sensors or components that could be possible causes of the problem. I dont need to go to the dealer for that. Otherwise i woudl jsut change the TPS IAC and VAF sensors and be done with it.

[FunctionSpec]

Idle Air control valve. Take it off and clean it thoroughly. Thick carbon probably came off and got caught into the screen of the idle air control valve

[Shroomster]

did you probe the 'new' sensor to see if its actually sending a signal?

able to obtain a copy of a service manual?


wait..wait....wait......

i-man cleaning with seafoam...first try checking the air filter....then try checking the pressure for the rail and then the injectors.....

[YarisSedan]

I think i have to agree with function. I jsut realized it the car has a very low idle which is why the car wants to die. Which will also set a code 31 the maf is functioning properly its detecting the low amount of air volume. Tomorrow i am going to remove the iac valve i bet its really gummed up. Only thing is i think i have to remove the throttle body to do that because of where the bottom screw of the valve is.

Only other thing i can think of is if the car hydrolocked and skipped timing.

[Bob_VT]

Ye Olde School..... ignoring codes and electronics for a moment (you said old ;) )

The shaky idle is normally caused by a vacuum leak. If it suddenly gets worse after something was done..... I would recheck the fuel system and hunt for the leak.

Now moving to modern times...... once a code is tossed with the CEL then the ecu will revert to a base program. There are I believe 4-5 systems that "check in" with the ecu on the toyota lexus (circa 1993).

If you did a top end cleaning I agree that something may have broken loose and is blocking a line.

I highly doubt it was " hydrolocked and skipped timing"

[Tamago]

not sure if it's been said yet, but try replacing the PCV valve.. it's a 2jz.. so there's plenty of opportunity for vacuum leaks

spray starting fluid around the engine bay on vacuum hoses and if you get a sputter, you've found a leaking point.

[IllusionX]

just a question though... Was it working fine before you tried to "fix" it ?
If so, why did you try to fix it when there wasn't any problems? :)


ok i'm not helping in any way..

[Tamago]

just a question though... Was it working fine before you tried to "fix" it ?
If so, why did you try to fix it when there wasn't any problems? :)


ok i'm not helping in any way..

do you not know what seafoam is?

[IllusionX]

it will dissolve carbon build ups on the pistons. but why? If there's no problems with the engine in the first place, i don't see why one would do that. Now his engine is not running fine and throws a check engine...

Anyways, i made my point. thank you. :)

[Tamago]

it will dissolve carbon build ups on the pistons. but why? If there's no problems with the engine in the first place, i don't see why one would do that. Now his engine is not running fine and throws a check engine...

Anyways, i made my point. thank you. :)

so, if it dissolves carbon buildup, wouldn't that help dissolve carbon buildup in the engine, thereby making the vehicle run better?

your attempt at sarcasm is so far a serious fail

[IllusionX]

hey.. my point is:

It's old, it's working. don't touch it. It's as simple as that.

No offense to YarisSedan, but good luck with the car.

[TLyttle]

It may be that I am just lazy (well, I am, really), but I agree with illusion: if it ain't broke, why fix it? SeaFoam has its place, but personally, I don't think that place is in a vehicle that is running fine.

[Tamago]

It may be that I am just lazy (well, I am, really), but I agree with illusion: if it ain't broke, why fix it? SeaFoam has its place, but personally, I don't think that place is in a vehicle that is running fine.

"fine" is relative..

[YarisSedan]

not sure if it's been said yet, but try replacing the PCV valve.. it's a 2jz.. so there's plenty of opportunity for vacuum leaks

spray starting fluid around the engine bay on vacuum hoses and if you get a sputter, you've found a leaking point.

Belive me i checked all that. I sprayed carb cleaner at base of intake manifold checked all vacuum lines removed the pcv valve and checked operation and then cleaned it with carb cleaner.


I think what im going to do tonight is remove the throttle body and clean it out and remove the idle air control valve. I am assuming its completely gummed up.


I did the seafoam to try to help him out. He was getting poor gas milage. I have done atleast 50 seafoam treatments with no problems. But i guess this particular car decided to act up. From now i i dont think i will do seafoam on any car that has more than 100k miles unless its been regularly serviced and maintained for fear of causing a problem. I guess live and learn.

[mikenacarato]

on my 93 lincoln i seafoamed and literally drove the crap out of it. all better. :)

[Tamago]

clogged IAC valve?

[GeneW]

Could also be the Oxygen sensor, a borderline condition that does not trigger a check engine light but may be deranging mixture settings enough to cause the system to target something else that governs mixture.

There may also be issues with exhaust gas recirculation, if the vehicle has such a device, since carbon deposits may have broken lose and stuck it open or closed. I think most modern cars use an EGR because it reduces pre-detonation and improves NOx emissions by changing the chemistry of the combustion.

Another, more awful possiblity, is that you've compromised oil control by loosening up some carbon around the oil rings and now you have blow by. Easy to check, run the engine hot and see if there is "puffing" when the oil filler cap is removed, in really bad cases the dipstick holder will also "puff" blowby.

Another possibility is that your carbon removal trick has clogged the catalytic converter. You can test this problem by driving the vehicle under load - like up a hill - it will lose power rapidly going up hill. A clogged catalytic converter will cause issues with idling too.

Gene

[YarisSedan]

Could also be the Oxygen sensor, a borderline condition that does not trigger a check engine light but may be deranging mixture settings enough to cause the system to target something else that governs mixture.

There may also be issues with exhaust gas recirculation, if the vehicle has such a device, since carbon deposits may have broken lose and stuck it open or closed. I think most modern cars use an EGR because it reduces pre-detonation and improves NOx emissions by changing the chemistry of the combustion.

Another, more awful possiblity, is that you've compromised oil control by loosening up some carbon around the oil rings and now you have blow by. Easy to check, run the engine hot and see if there is "puffing" when the oil filler cap is removed, in really bad cases the dipstick holder will also "puff" blowby.

Another possibility is that your carbon removal trick has clogged the catalytic converter. You can test this problem by driving the vehicle under load - like up a hill - it will lose power rapidly going up hill. A clogged catalytic converter will cause issues with idling too.

Gene

I was thinking some of those things. I dont belive the cat is clogged since seafoam is usually supose to clean the cat. EGR malfunction is possible since a egr comming on at idle will cause issues.

I think tonight or tomorrow ill remove the throttle body and clean the iac valve first before anything. I am hoping that does the trick. I am changing the spark plugs since i have the intake off since they are worn and the incorrect one even though i dont think its the cause of the problem.

Hopefully that takes care of it. If not i guess egr is next step. I am glad there are many mechanics here on ayrisworld to bounce ideas off of. Its liek a real world house episode but with cars =)

[Shroomster]

why haven't you checked the lymph nodes yet? ^^^^ hehe

[GeneW]

I was thinking some of those things. I dont belive the cat is clogged since seafoam is usually supose to clean the cat.

If you're still having issues after you've tried some things, reconsider the cat converter. Worst times I've had troubleshooting was when I assume that things were "not supposed to happen" and ended up happening.

Gene

[Bob_VT]

The seafoam will not clear a clogged cat and actually it will add crap to the honeycomb.

How is the higher end of the rpms doing? It could just be having a cloud of crap through the whole system. Need to drive it a bit at highway speeds.

[YarisSedan]

Okay took the throttle body off today with the cost of my back. Tonight i have to sleep with my feet elevated on pillows and tons of advil and hope for the best in the morning.

But the throttle didnt look terribly bad. I cleaned it all out. Removed the iac and it was covered in carbon. Sprayed as much carb cleaner as i could and wiped it clean and cleaned the iac passages. Tomorrow will start to assemble everything back together and hope for the best. I havent really taked it on the freeway. I may have to take it out and drive it hard and hopefully blow out all the rest of the carbon.

[YarisSedan]

Hmm put everything back together and its doing the same thing. I noticed that when the car is cold it runs beautifully but once it warms up is when it starts to act up.

[FunctionSpec]

Check for a vacuum leak. Intake hose is probably hard and brittle esp on an old car like that. Probably developed a crack when moving around the hose to clean out the intake manifold. Hot and cold start situations might affect it because the movement of the engine at higher cold idle and lower hot idle closes off the crack or opens it up.

Also check all the other little hoses for cracks and leaks.

[YarisSedan]

I checked for vacuum leaks actually all vacuum hoses and the intake hose. Actually broke portion of the hose taking it off throttle so replaced it cause it was so brittle.

Going to drive the car to my shop saturday morning. That way no cars out at 7:30 in the morning so dosnt matter too much if it stalls int he middle of the street just start it up and keep driving. I am going to just check all the basics, fuel pressure, ignition timing, compression, vaccum. I have to stop assuming it was something i did and not a preexisting condition. Just test everything and verify till i narrow the options down.

[Shroomster]

UPDATE?

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